Category Archives: Science

Is queen clipping cruel?

Synopsis : Is clipping the queen a cruel and barbaric practice? Does it cause pain to the queen? Surely it’s a good way to stop swarming? This is an emotive and sometimes misunderstood topic. What do scientific studies tell us about clipped queens and swarming?

Introduction

After the contention-free zone of the last couple of weeks I thought I’d write something about queen clipping.

This is a topic that some beekeepers feel very strongly about, claiming that it is cruel and barbaric, that it causes pain to the queen and – by damaging her – induces supersedure.

Advocates of queen clipping sometimes recommend it as a practice because it stops swarming and is a useful way to mark the queen 1.

I thought it would be worth exploring some of these claims, almost all of which I think are wrong in one way or another.

1002, 1003, 1004, 1005, er, where was I? Damn!

Here’s one I didn’t lose earlier – swarm with a clipped queen from the bee shed

I clip and mark my queens.

You can do what you want.

This post is not a recommendation that you should clip your queens. Instead, it’s an exploration of the claimed pros and cons of the practice, informed with a smattering of science to help balance the more emotional responses I sometimes hear.

By all means do what you want, but if you oppose the practice do so from an informed position.

Having considered things, I believe that the benefits to my bees outweigh the disadvantages.

And I deliberately used the word ‘bees’ rather than ‘me’ in the line above … for reasons that should become clear shortly.

What is queen clipping?

Bees have four wings. The forewings 2 are larger and provide the most propulsive power.

Each wing consists of a thin membrane supported by a system of veins. The veins – at least the larger veins – have a nerve and a trachea running along them. Remaining ‘space’ in the vein is filled with haemolymph as the veins are connected to the haemocele.

Queen ‘clipping’ involves using a sharp pair of scissors to remove a third to a half of just one of the forewings.

Done properly – by which I mean cutting enough from one wing only whilst not amputating anything else (!) – significantly impairs the ability of the queen to fly.

She will still attempt to fly but she will have little directional stability and is unable to fly any distance.

Easy to see

Easy to see – clipped and marked queen

It shouldn’t need stating 3 but it’s only sensible to clip the wing of a mated, laying queen.

Although you can mark virgin queens soon after emergence – before orientation and mating flights 4 – clipping her wing will curtail all mating activity 5.

How to clip the queen

If I know I want to mark and clip a queen I find my Turn and Mark cage, Posca pen and scissors. The cage is kept close to hand, the pen and scissors are left in a semi-shaded corner of the apiary.

Tools of the trade – Turn and Mark cage, Posca pen and sharp scissors

Then all you need to do is:

  • Find the queen, pick her up and place her in the cage. Leave the caged queen with the pen/scissors while the frame is returned to the hive 6.
  • Holding the cage in my left hand and scissors in my right I gently depress the plunger and wait until she reverses, lifting one forewing through the bars of the cage. At that point I depress the plunger a fraction more to hold her firmly in place.
  • Cut across the forewing to reduce its length by 1/3 to 1/2. Be scrupulously careful not to touch the abdomen with the scissors, or to sever a leg by accident 7.
  • Mark the queen with a single spot of paint on her thorax then leave the queen in the cage for a few minutes while the paint dries.
  • Return the queen to the hive. The simplest way to do this is to remove the plunger and lay the barrel of the cage on the top bars of the frame over a frame of brood. The workers will welcome her and, in due course, she’ll wander out and down into a seam of bees.

Returning a marked and clipped queen to a nuc

Don’t real beekeepers just hold the queen with their fingers?

Probably.

Maybe I’m not a real beekeeper 😉

I prefer to cage the queen before clipping and marking her.

I wear nitrile or Marigold gloves (or one of each) to keep my fingers propolis free. If the gloves are sticky with propolis I don’t want this coating the queen. I also prefer to keep my scents and odour off the queen 8.

The other reason I prefer to cage the queen is to reduce the potential for damaging her with the scissors.

You’d have to be even more cackhanded than me 9 to pierce the abdomen of a caged queen with the scissors. In addition, her ability to raise a hind leg up and through the bars of the cage is restricted. In contrast, when held in the fingers, both these can be more problematic.

Mr Blobby goes beekeeping

Finally, briefly caging the queen allows me to use both my hands for other things – like completing the colony inspection without any risk of crushing the queen.

Yes, I could unglove before clipping and marking the queen, but it’s almost impossible to get nitriles back on if your hands are damp.

Does queen clipping stop swarming?

No.

Is that it? Nothing more to say about swarming?

OK, OK 😉

If the queen is not clipped the colony will typically swarm on the first suitable day after the new queen cell(s) in the hive are sealed. The swarm bivouacs nearby, the scout bees find and select a suitable new nest site and the bivouacked swarm departs – often never to be seen again – to set up home.

I’ll return to the subsequent fate of the swarm at the end of this post.

A colony with a clipped queen usually swarms – by which I mean the queen and up to 75% of the workers leave the hive – several days after the new queen cell(s) is capped.

Ted Hooper 10 claims a colony headed by a clipped queen “swarm(s) when the first virgin queen is ready to emerge” 11. This is not quite the same as when the first virgin emerges.

Since queen development takes 16 days from the egg being laid this theoretically means you could conduct inspections on, at least, a fortnightly rota. Unfortunately, it’s not quite that simple as bees could choose an older larva to rear as a new queen.

Hooper has a page or so of discussion on why a 10 day inspection interval achieves a good balance between never losing a swarm and minimising the disturbance to the colony. 12.

What happens when a colony with a clipped queen swarms?

A clipped queen cannot fly, so when she leaves the hive with a swarm she crashes rather unmajesterially 13 to the ground.

In my experience there are two potential outcomes:

  • the bees eventually abandon her and return to the hive. Usually the queen will perish. They are still likely to swarm when the virgin queen(s) emerge. All together now … “queen clipping does not stop swarming”.
  • the queen climbs the leg of the hive stand and often ends up underneath the hive floor. The bees join her. In this case you can easily retrieve the swarm together with the clipped queen. Temporarily set aside the brood box and supers and knock the clustered bees from underneath the floor into a nuc box.

I spy with my little eye … a clipped queen that swarmed AND was abandoned by the bees. It’s a tough life.

Sometimes both the queen and the swarm re-enter the hive (or I return them to the hive). In my experience these queens often don’t survive, presumably being slaughtered by a virgin queen.

So that addresses the swarming issue 14. What about the more contentious aspect of queen clipping causing pain?

Do queens feel pain?

I discussed whether bees feel pain a couple of years ago. The studies on self-medication with morphine following amputation are relevant here. Those studies were on worker bees, but I’ve no reason to think queens would be any different 15. I’m not aware of more recent literature on pain perception by honey bees though it’s well outside my area of expertise, so I may have missed something.

Therefore, based upon my current understanding of the scientific literature, I do not think that worker bees feel pain and I’m reasonably confident that queens are also unlikely to feel pain.

It’s worth noting here that it’s easy to be anthropomorphic here, particularly since we (hopefully) all care about our bees. Saying that your bees are happy, or grumpy or in pain, because it’s a nice day, or raining or you’ve just cut her wing off, are classic examples of ascribing human characteristics to something that is non-human.

We might think like that 16 but it’s a dangerous trap to fall into.

Is clipping queens cruel and barbaric?

According to my trusty OED, cruel means “Of conditions, circumstances: Causing or characterized by great suffering; extremely painful or distressing.”

Therefore, if clipping a queen’s wing causes pain and distress then it should be considered a cruel practice.

I’ve discussed pain perception previously (see above). If bees, including queens, do not feel pain then clipping her wing cannot be considered as cruelty.

Someone who is barbaric is uncultured, uncivilised or unpolished … which surely couldn’t apply to any beekeepers? In the context of queen clipping it presumably means a practise known to cause pain and distress.

Having already dealt with pain that brings me to ‘distress’.

How might you determine whether a queen with a clipped wing is distressed?

Perhaps you could observe her after returning her to the colony? Does she run about wildly or does she settle back immediately and start laying again?

Returning a marked and clipped queen – no apparent distress, just calmly disappearing into a seam of bees

But, let’s take that question a stage further, how would you determine that it was the clipped wing that was the cause of the distress? 17

That pretty much rules out direct observation. Queens are naturally photophobic 18 so you’d need to use red light and an observation hive. I’m not aware that this has been done.

Instead, scientists have observed the performance of colonies headed by clipped and unclipped queens. I’d argue that this is a convenient and suitable surrogate marker for distress. You (or at least I) would expect that a queen that was in distress would perform less well – perhaps laying fewer eggs, heading a smaller colony that collected less honey etc.

Are clipped queens distressed? Is their performance impaired?

Which finally brings us to some science. I’ve found very little in the scientific literature about queen clipping, but there is one study dating back over 50 years from Dr I.W. Forster of the Wallaceville Animal Research Centre, Wellington, New Zealand 19. I can’t find a photo of Dr. Forster, but there’s an interesting archive of photos from the WARC provided online from the Upper Hutt City Library.

Wallaceville Animal Research Centre staff photo 1972. Presumably Dr. Forster is somewhere in the group.

The paper has a commendably short 37 word results and discussion section 😉  20

The study involved comparing performance of colonies headed by clipped or unclipped queens over three seasons (1968-1970), a total of 124 colony years. They 21 scored colony size (brood area), honey per hive (weight) and the the number of supersedures.

I’ll quote the single sentence in the results/discussion on honey production in its entirety:

There was no significant variation in honey production between hives headed by clipped and unclipped queens.

Forster 22 didn’t specifically comment on colony size/strength in the discussion. Had it differed significantly some convoluted explaining would have been needed to justify the similarity in honey production.

Comparative colony strength of colonies headed by clipped or unclipped queens.

And it doesn’t.

Each column represents the average number of frames of brood in 6-29 colonies headed by clipped or unclipped queens. Statistically there’s no also difference in this aspect of performance (entirely unsurprisingly).

Colonies headed by clipped queens are not impaired in strength or honey production, so I think it’s reasonable to assume that the queen is probably not distressed.

Do clipped queens get superseded (more) frequently?

I suspect most beekeepers underestimate supersedure rates in their colonies.

I clipped and marked a queen last weekend. In early August last year my notes recorded her as ’BMCLQ’ i.e. a blue marked clipped laying queen 23. In mid/late April this year she was unmarked and unclipped … and stayed that way until it was warm enough to rummage through the hive properly.

She’s now a YMCLQ 24 and was clearly the result of a late season supersedure.

Every spring I find two or three unmarked queens in colonies. Sometimes it’s because I’d failed to find and mark them the previous season. More usually it’s because they have been superseded.

The Forster study recorded supersedure of clipped and unclipped queens. It varied from 10-25% across the two seasons tested (’68 and ’69) and was fractionally lower in the clipped queens (20% vs. 22.5%) though the difference was not significant.

So, to answer the question that heads this section … yes, clipped queens do get superseded 25. However, done properly they do not show increased levels of supersedure 26.

Let’s discuss swarming again

In closing let’s again consider the fate of swarms headed by clipped or unclipped queens.

If a colony with the clipped queen swarms the queen will either perish on the ground, or attempt to return to the hive. If the swarm abandons her they will return to the hive … but may swarm again when the first virgin emerges.

If she gets back to the hive she may be killed anyway by a virgin queen.

You might lose the queen, but you will have gained a few days.

If a colony with an unclipped queen swarms … they’re gone.

Yes, you might manage to intercept them when they’re bivouacked. Yes, they might end up in your bait hive. But, failing those two relatively unlikely events, you’ve lost both the queen and 50-75% of the colony.

What is the likely fate of these lost swarms?

They will probably perish … either by not surviving the winter in the first place, or from Varroa-transmitted viruses the following season.

Studies by Tom Seeley suggest that only 23% of natural swarms survive their first winter. Furthermore, the survival rates of previously managed colonies that are subsequently unmanaged – for example, the Gotland ‘Bond’ experiment – is less than 5%.

Let’s be generous … a lost swarm might have a 1 in 4 chance of surviving the winter, but its chances of surviving to swarm again are very slim.

Anecdotal accounts of ’a swarm occupying a hollow tree for years’ are common. I’m sure some are valid, but tens of thousands of swarms are probably lost every season.

Where does that number come from?

There are 50,000 beekeepers in the UK managing 250,000 colonies. On average I estimate I lose swarms from 5-10% of my colonies a season, and my swarm control is rigorous and reasonably effective 27. If there were over 25,000 swarms ‘lost’ a year in the UK I would not be surprised.

Free living colonies are not that common, strongly suggesting most perish.

Where do these ‘lost’ swarms go?

There are four obvious possibilities. They:

  1. voluntarily occupying a bait hive and become managed colonies
  2. occupy a hollow tree or similar ‘natural’ void
  3. set up a new colony in an ‘unnatural’ void like the roof space of a children’s nursery or the church tower
  4. fail to find a new nest site and perish
Natural comb

A colony settled here and subsequently perished

Of these, the first means that it’s likely the colony will be managed for pests and disease, so their longer term survival chances should be reasonably good.

In contrast, the survival prospects for unmanaged colonies are bleak. They will almost certainly die of starvation or disease.

What about the lost swarm that occupies the loft space in the nursery or the church tower? Whether they survive or not is a moot point (and the same arguments used for ‘bees in trees’ apply here as well). What is more important is that they potentially cause problems for the nursery or the church … all of which can be avoided, or certainly reduced, if the queen is clipped.

And if you conduct a timely inspection regime.

Why I clip my queens

Although it is convenient to reduce the frequency of colony inspections, that is not the main reason I clip my queens.

I clip my queens to help keep my worker population together, either to increase honey production or to provide good strong colonies for making nucs (or queen rearing).

This has the additional benefit of not imposing my swarms and bees on anyone else. Whilst I love my bees, others may not.

An additional, and not insignificant, benefit is that the prospects for survival of a ‘lost’ swarm are very low.

By reducing the loss of swarms I’m “saving the bees”.

More correctly of course, I’m preventing the loss of an entire colony. I think clipping queens is therefore an example of responsible beekeeping.

I also think queen clipping is acceptable as I’ve seen no evidence – from my own beekeeping or in the literature – that it is detrimental to the queen or the colony.

Thou shalt not kill

Finally, there are some that argue you should never harm or kill a bee. I have two questions in response to that view;

  • What do you do with a queen heading up a truly psychotic colony? Do you kill her and replace her or do you put up with the aggravation and make the area around the hive a ‘no go zone’ for anyone not wearing a beesuit?
  • How many beekeepers can honestly say that no bees are harmed when returning frames during an inspection, or putting heavy supers back on a hive? 28

I would have no hesitation in killing and replacing a queen heading an aggressive colony.

Again, I think that’s responsible beekeeping.

Similarly, although I’m as careful and gentle as I can be when conducting inspections or returning supers, to think that no bees are ever injured or killed is fantasy beekeeping.


Note

This is an emotive topic and I’ve written far more than I’d intended – that’s due to a couple of days of rain and the ‘expectant father’ wait for my new queens to start laying. I could have written half as much again.

The time spent writing meant I’ve not done an exhaustive literature search. I know that Brother Adam wrote in 1969 that he’d clipped queens for over 50 years without noticing any disadvantages. I realised during the week that my American Bee Journal subscription has lapsed so I’ve not managed to go through back issues, though I have searched almost 30 years of correspondence on Bee-L. If an ABJ turns up more relevant information I’ll revisit the subject.

Timing is everything

Synopsis : The invariant timings of brood development dictate many beekeeping events including colony inspections, queen rearing and Varroa management. It makes sense to understand and exploit these timings, rather than ignore or fight against them.

Introduction

There are some inherent contradictions involving timing in beekeeping that can confuse beginners. Actually, they can confuse anyone – beginner or old lag 1 – who doesn’t appreciate the considerable flexibility of some of the timings and the near-total inflexibility of others.

I think that many of the inherent difficulties in beekeeping e.g. judging when to do what to the colony, comparing seasonal differences or deciding whether intervention is needed or ill advised, are due to a lack of appreciation of the relative importance of some of these timings.

I gave an overview of some of the ‘flexible timings’ a couple of weeks ago when discussing the year to year climatic variation that compounds differences caused by latitude.

The onset of brood rearing in midwinter, the crossover date 2, the start of swarming and the timings of the major and minor nectar flows can all vary from year to year.

To appreciate these you need to be observant, but predicting their impact can be tricky. Some are multi-factorial e.g. colony strength and development in a warm, dry spring can be different to a warm, wet spring.

I’ve probably written enough about some of these flexible events already so will instead focus on some of the ‘inflexible timings’ that dictate the activity of the colony and, by extension and through necessity, the activity of the beekeeper.

In many ways these are easier to understand.

By definition, they are invariable 3.

Less to remember … but remembering them is important 😉

The environment

Those ‘flexible timings’ I refer to above mainly reflect the year-to-year climatic variation – warm springs, Indian summers, hard winters.

In contrast, inside the hive the environment is remarkably stable.

It can vary from 4°C to 40°C outside – even on a single day – but the temperature in the brood nest is controlled within a narrow 33-36°C range.

Hives in the snow

Freezing outside, 34.5°C in the broodnest

In fact, in the very centre of the brood nest – the region where pupal development takes place – it is as near as makes no difference 34.5°C.

The workers thermoregulate the hive, heating the comb where needed 4 or evaporating water to cool the hive.

With hive monitoring equipment and suitably placed thermometers you can tell when a colony shifts into brood rearing mode in the spring – the varying temperature of the clustered bees increases and stabilises to a near-invariant 34 and a bit degrees Centigrade.

Brood rearing starts ...

Brood rearing starts – indicated by stabilisation of brood temperature (arnia.co.uk)

The image above is from Arnia who make hive monitoring equipment. The key phrase in the sentence above is ‘suitably placed thermometers’. You tend to have only one or two and they can’t be everywhere, so it’s easy to miss the onset of brood rearing.

Temperature, behaviour and neuroanatomy

Stable temperatures are important for brood development. Worker bees reared at 32°C are less good at waggle dance communication. They only complete about 20% of the circuits (less enthusiastic) and exhibit more variability in the duration of the waggle phase (the distance component) when compared to bees reared at higher temperatures within the ‘normal’ range 5.

In further studies, bees reared at abnormally low or high temperatures (though varying by only 1-2 °C from normal hive temperatures) exhibited differences in neuroanatomical development 6. Of the regions of the brain studied, the numbers of microglomeruli within the mushroom bodies of the brain, areas involved in memory and learning, differed significantly when the pupation temperature was as little as 1°C over or under 34.5°C.

Despite these behavioural and developmental differences, the emergence rate and the duration 7 of development are somewhat less influenced by brood nest temperature.

Influence of temperature on pupal brood development – duration (left axis) and emergence rate (right axis)

In the graph above the duration of pupal development is 10-11 days between 34.5°C and 37°C, and eclosion (emergence) rates exceed 90% from 31-36°C.

Correct development of honey bee workers therefore requires a stable brood nest temperature.

As a consequence of this stability the duration of the development cycle is highly reproducible and – more to the point – predictable.

Before discussing the development cycle it’s worth noting that queens and drones are reared under similarly stable conditions. I’ve discussed the influence of temperature on queen development before but am unaware of similar studies on drones.

The development of workers

The graph above shows the influence of temperature on the duration of pupal development. This is not the same as sealed brood development. 8. The 10-11 days shown above needs to be extended by 2 days (48 hours) when considering the more beekeeper-friendly concept of sealed or capped brood.

Under normal conditions worker development takes 21 days. Three days as an egg, five as an open larva and 13 capped 9.

During those 21 days bees go through a series of six molts between five developmental stages termed instars. The first molt is the egg hatching, molts 2-4 occur during the first few days of larval feeding. Molt 5 is the change from the pre-pupal capped larva to the pupa and the final molt occurs at emergence.

Once the brood is capped there’s nothing much the beekeeper needs to worry about (or can do). In contrast, the early days of worker development involve at least one notable event 10.

Young larvae and queen rearing

The worker larva is fed progressively, which essentially means almost all the time. Nurse bees visit the larva thousands of times, initially feeding a mix of secretions from the hypopharyngeal and mandibular glands. The diet is then switched to one lacking the mandibular gland component and is finally supplemented with pollen and honey.

This dietary switch takes place around day three of larval development and effectively seals the fate of the developing bee as a worker.

Before day three of larval development, larvae destined to be workers or queens receive the same diet. After day 3 a series of genetic switches are ‘pushed’ that prevent the larva developing into a queen.

This means that larvae of less than three days old are needed to produce new queens. A terminally queenless colony will sometimes attempt to rear a new queen from an older larva (if nothing else is available) but these are usually substandard – so called scrub queens – or fail.

The adult worker

After emergence the worker fulfils a number of roles for the colony; nurse bee, comb builder, guard, scout, forager etc. The precise timings of these are flexible. Not all bees of the same age have the same role, and they can even be reversed. However, as far as practical beekeeping is concerned 11, the only other timings that really matter are the longevity of workers; in the summer this is about 6 weeks and in the winter, 6 months.

The timings to remember – workers

The full development cycle takes 21 days. Larvae more than 3 days old 12 are unsuitable for queen rearing (and, as I shall discuss in a future post, better queens are produced from younger larvae). The adult worker spends the first half of her 6 week life within the hive, and the last 3 weeks as a forager. Winter bees live for many months.

The development of queens

The development cycle of the queen bee is shorter than that of the worker because their diet is much richer. Of course it’s not quite that straightforward (it wouldn’t be, would it?). Because of the diet there are a number of genetic pathways turned on or off in the developing queen that ensure she is ‘fit for purpose’ on emergence. The developing queen goes through the same number of molts and instars, but they are compressed in time.

Sealed queen cell ...

Sealed queen cell

The queen cell is sealed on the ninth day of development, the fifth day after hatching from the egg, and the queen emerges on the 16th day.

The adult queen

Relative to workers and drones the queen appears almost immortal. A queen may live for at least three years and, if well looked after, longer than that. Most of this aftercare is provided by the hive, but the beekeeper can influence things as well. High quality ‘breeder queens’ are often kept in nucs and discouraged from laying excessive amounts of brood. This prolongs their effective lifespan.

As far as timings are concerned – and assuming we’re not dealing with a $500 breeder queen – the only three things that are important relate to the mating of the queen.

After emergence the queen needs to reach sexual maturity before she can go on her mating flights, this takes 5-6 days. Once mated there is a further delay of 2-3 days before the queen starts laying. The final number to remember is that adult queens older than 26-33 days are too old to mate.

The timings to remember – queens

The full development cycle takes 16 days. The cell is capped on the 9th day after the egg was laid 13. Upon emergence, queens take 5-6 days before they are mature enough to mate. A mated queen starts laying 2-3 days after returning from her last mating flight. If they’re not mated within about 4 weeks of emergence then they’ve blown it.

Therefore, the minimum duration to go from newly laid egg to mated, laying queen is at least 23 days. Alternatively, assuming a 2-3 day old larva is available, this time period is reduced to about 18 days.

From emergence, it’s theoretically possible 14 to have a mated, laying queen within 8 days.

However, in my experience, queen mating usually takes longer than these minima … and always longer than I want. Other than confirming emergence I always leave a new queen a minimum of a fortnight before checking if she’s laying, and longer if the weather has been unsuitable for mating.

The development of drones

Like teenage boys getting up late and then doing nothing other than lounge around eating and thinking about sex 15, the drone takes the longest to emerge. The full development cycle from the laying of an unfertilised egg to emergence takes 24 days.

As before, the number of molts and instars are the same as undergone by queens and workers.

The adult drone

Like the queen, the drone needs to become sexually mature before going on a mating flight. This takes 10-12 days after emergence. The drone has a finite lifespan and usually lives no more than about a month during the summer.

Drones that successfully mate with a queen prematurely die. Those that don’t mate either die trying or are ejected from the hive by the workers at the end of the season.

It’s not unusual to hear beekeepers talk about finding drones overwintering. I’m not aware whether these are exceptionally long-lived drones laid by the queen the preceding summer/autumn, or laid by a failing queen during the winter, or even by laying workers in a queenless colony overwinter 16.

The timings to remember – drones

The full development cycle takes 24 days. It takes about five weeks between the appearance of the first eggs in drone cells and the presence of sexually mature drones in the hive.

Swarming cannot happen until there are drones in the area, so it’s worth keeping an eye of drone brood production.

Hive inspections and queen rearing

So, there you have it, just a few numbers to remember … and, more importantly, to understand their significance for beekeeping.

Unusually I’ve prepared an oversized figure to illustrate these timings 17 with colour-coding worker, queen and drone events in green, blue and red respectively.

Worker, drone and queen development and key post-emergence timings

Note that some timings have dual significance. Worker larvae no more than three days old (day 6 – in green) can be reared as queens with suitable feeding.

Hive inspections … and caveats

It should now be obvious why regular weekly hive inspections are recommended in the time leading up to and during the peak swarming period.

If there are no charged queen cells – those containing eggs or developing larvae – during an inspection then any that do develop in the seven days before the next inspection will still not be sealed (and therefore the colony will not have swarmed).

This assumes that the colony swarms on or after the day that the queen cell is sealed.

Sometimes – rarely – the swarm goes early, apparently leaving only uncapped swarm cells. When I’ve had this happen a thorough examination of the brood frames has sometimes turned up a sealed cell, tucked away against a sidebar, that I’d missed in the previous inspection … the colony had not swarmed early, I’d 18 not been observant enough.

With a well-populated colony it’s sometimes necessary to shake all the bees off each frame to be certain there are no queen cells lurking under the ruffled curtain of workers.

Not all queen cells are this obvious

Colonies containing clipped queens tend to delay swarming (but they certainly still swarm) and you can usually get away with a 10 day interval between inspections. Furthermore, since the clipped queen cannot fly, even if the colony does swarm they usually return and end up clustered underneath the OMF after she has crawled back up the leg of the hive stand.

Outside the main swarming period inspections can be much less frequent. I usually inspect only once or twice between mid-July and the end of the season.

Queen rearing

One of my (few) poorly tempered hives unexpectedly contained several 3+ day old queen cells last Sunday. I made up a nuc with the old queen, destroyed all the queen cells and closed up the hive.

They will produce more queen cells 19, but they cannot swarm as there’s no queen.

At my inspection this Sunday I will destroy all the new queen cells.

The genetics of this colony are (at best) ‘undesirable’ 🙁 

Since there’s been no laying queen in the hive for 7 days there cannot now be any larvae young enough to be reared as a new queen 20. Therefore, having destroyed all the queen cells, I’ll add a frame of eggs and larvae from a (well-behaved and so genetically desirable) neighbouring colony 21.

If they want a new queen 22 they will rear one from this donated frame.

The 23 egg in the graphic above is the earliest you can expect a laying queen. In reality – as explained above – it usually takes longer. A minimum of 30 days from egg to egg-producing queen is perhaps more dependable.

Therefore, in around 24 to 30 days – and most likely the latter – this colony will have a new queen which will hopefully improve their behaviour.

The timing of Varroa treatment(s)

But think about what’s happening to the rest of the brood in that colony.

The last eggs laid in the colony was on the Sunday the 1st of May. By the 21st of May all the worker brood will have completed development and emerged. By the 24th of May all the drones will have emerged.

The colony should therefore be broodless in the last week of May.

Even if the new queen is laying by then (some chance!) she won’t have produced any sealed brood.

If needed I could use this 7 day window of opportunity to treat the colony with oxalic acid and reduce the Varroa levels in the hive.

It’s unlikely I’ll need to as the mite numbers have been low this season. However, it’s very reassuring that I have the option should I need it 24.

Adding a Varroa board to check mite drop

But … hang on a moment.

Why did I write that the colony only should be broodless?

What about the eggs and larvae on the frame I added from the donor colony? 25

These will be up to one week younger than any brood in the queenless colony.

Potentially those young eggs and larvae will close that ’window of opportunity’.

Perhaps the easiest way around this is to excise one good sealed queen cell from the donated frame and leave it in queenless colony, and then remove the donated frame and use it elsewhere.

If the colony produces several good quality queen cells it’s likely that I’ll chop them all out and make up some nucs – queen rearing without all the graft.

Literally 😉

Conclusions

I’ve written far more than I intended but I think this reflects the importance of the – effectively invariant – timings of brood development.

These dictate so many of our beekeeping activities that it makes sense to learn to work with them, rather than forever struggling against them.

With good observation and regular colony inspections – weekly during the the main part of the season – there should be little or no chance of losing a swarm.

Furthermore, should a colony show signs of swarm preparation, timely intervention coupled with an appreciation of the timings of brood development, mean you have the opportunity to conduct both stock improvement and mite management.

Nice one 😉


 

Brood in all stages

Synopsis : The presence of brood in all stages (of development) is an important indicator of the state of your colony. Is it queenright? Is it expanding or contracting? Quantifying the various developmental stages – eggs, larvae and pupae – is not necessary, but being able to determine changes in their proportions is very useful.

Introduction

There’s something very reassuring about the words ’brood in all stages’ to a beekeeper, or at least to this beekeeper.

It means, literally, that there is brood in all stages of development i.e. eggs, larvae and pupae.

Record keeping

Update the notes …

As far as I’m concerned, it’s such an important feature of the hive that it gets its own column in my hive records, though the column heading is conveniently abbreviated to BIAS.

And BIAS is what I’ll mostly use for the remainder of this post, again for convenience.

Why is it so important?

Why, when you conduct an inspection of the colony, is the presence of BIAS so important?

And why should you be reassured if it is present?

Broadly I think there are two reasons:

  • it tells you the likely queenright status of the hive. Is there a laying queen present?
  • (with a little more work) you can determine the egg laying rate of the queen and whether it’s changing. This is important as it provides information of the likely adult worker strength of the colony in a few weeks’ time. Are there going to be enough bees to exploit the expected nectar flow? Will there be sufficient young bees for queen rearing?

Of course, detailed scrutiny of the eggs, larvae or pupae in the hive can provide a wealth of information about the health of the colony. I will mention one specific example later, but it’s not the main focus of this post.

The development cycle of the honey bee

The post last week emphasised the variation – from year to year – in the climate 1. In contrast, despite the temperature fluctuating outside the hive, the environment inside the hive is remarkably stable. Partly as a consequence of this the development of the brood is very predictable.

Honey bee development

Honey bee development

Worker bees take 21 days to develop, by which I mean that an egg laid on day 1 will – assuming development is successful – result in an adult worker emerging 2 on day 21. There can be a few hours variation, largely influenced by temperature, but as far as we need to be concerned here worker bee development takes 21 days.

Days 1 to 3 are spent as an egg. The egg then hatches to release a larva which is fed for a little over five days before capping. The developing bee then pupates for about 13 days before emergence.

For simplicity it helps to think of the development cycle as 3 days as an egg, 5 days as a larva and 13 days as a pupa. EEELLLLLPPPPPPPPPPPPP 3 or 3:5:13 … I’ll return to these numbers later.

In fact it’s a little more complicated than that. The larva actually pupates after the cell is capped, so it exists in two states; an open larval stage during which is is fed by nurse bees and a capped larval stage which is more correctly termed the pre-pupal stage. The larva then metamorphoses into a pupa within the capped cell.

None of this really matters as far as your interpretation of the ’brood in all stages’ you see in the colony during a regular inspection. However, it’s reassuring to know that there’s lots of complicated things with weird names and confusing terminology going on in there … which I’ve simplistically distilled to 3:5:13.

But, if you do want to know more you could have a read of this article by Rusty Burlew which also appeared in the American Bee Journal 160:509-511 (2020).

Queenright or not?

So, if there are eggs present there must be a queen present, right?

Wrong 🙁

But it is more than likely 🙂

In fact, if there are eggs, larvae and sealed brood present i.e. BIAS, then you can be pretty confident there is a queen present.

Or, more correctly, that there was a queen present within the last 3 days.

If an egg takes three days to hatch then it is possible that the queen laid the eggs and has subsequently disappeared.

For example, the colony may have swarmed in the intervening period.

Alternatively, during that ’quick-but-entirely-unnecessary-peek’ you took inside the hive two days ago you inadvertently crushed the queen between the bars of a Hoffman frame.

Oops … eggs but no queen 🙁

Slim Jim Jane and pre-swarming egg laying activity

When a colony swarms the mated, laying queen leaves with the swarm. To ensure that she can fly sufficiently well she is slimmed down in the days before swarming and her egg laying rate slows significantly.

Despite searching – both the literature and my own memory banks 4 – I’ve failed to find any detailed information on how long before swarming her laying rate slows. It appears as though she generally does not stop laying before swarming, but it’s down to just a trickle (if that’s the right word) in comparison to when she’s ‘firing on all cylinders’.

Queen cells and laying workers

The other telltale sign that a swarmed colony leaves is the presence of one or (usually) more queen cells. Typically some of these are capped, with the colony swarming on the first suitable day after the first cell is capped.

Queen cells – good and bad

So, back to your colony that may or may not be queenright … the presence of only a small number of eggs compared to capped brood levels and one or more queen cells suggests that they have swarmed within the last 3 days.

In contrast, If there are ‘normal looking’ eggs present, even if few in number, and you didn’t have a ’quick-but-entirely-unnecessary-and-actually-a-bit-clumsy-peek’ two days ago, it’s likely that your colony is queenright.

I prefixed eggs (above) with ‘normal looking’ because there is one further situation when the colony has no queen but there are eggs present. That’s when the colony has developed laying workers.

Under certain conditions unmated worker bees can lay unfertilised eggs.

However, in contrast to the queen, workers have short, dumpy abdomens and cannot judge whether the cell already contains an egg. As a consequence they lay multiple eggs in cells and many of these eggs are in unusual positions – rather than being central at the bottom of the cell they are on the sidewalls, or the sloping edges of the base of the cell.

Drone laying workers ...

Multiple eggs per cell = laying workers (usually)

These eggs are usually laid in worker cells. Being unfertilised they can only develop into drones, and since they are in cells that are too small for drones they end up protruding like little bullets from the comb.

Laying workers ...

Laying workers …

They are also scattered randomly around the frame, rather than being in the concentric ring pattern used when the queen lays up a frame.

BIAS and the queenright status of the colony

So, let’s summarise that lot before (finally) getting back to 3:5:13.

If:

  • there is BIAS and no queen cells present and you’ve not disturbed the colony in the last few days … then the colony is most likely queenright. Yes, there’s an outside chance she recently dropped dead, but it’s much more likely that you just can’t find her. Don’t worry, the presence of BIAS and the other supporting signs tell you all you need to know … there’s a queen present and she’s laying. All is good with the world. Be reassured 🙂
  • there is BIAS and capped queen cells … then it’s likely they swarmed very recently 🙁
  • eggs are present, possibly together with some small, unsealed queen cells and you had a ’quick-but-entirely-unnecessary-and-frankly-a-bit-stupid-in-retrospect-peek’ two days ago … then all bets are off. The colony may or may not be queenright. Only inspect when you need to and be very careful returning frames to the hive 5. If you didn’t open the hive in the last few days (and accidentally obliterate the queen) the presence of BIAS and unsealed queen cells usually means that the colony is queenright but is preparing to swarm. Swarm control is urgently needed.
  • multiple eggs are present in strange places in cells, coupled with scattered bullet-shaped capped cells (and oversized larvae in worker cells) … then there are laying workers present. Your colony is not queenright. Technically I suppose there is brood in all stages, but the brood looks odd. But there’s somethings else as well … laying workers develop in the absence of pheromones produced by open brood (larvae). Therefore to develop laying workers a colony transitions through a period when there is not brood in all stages. In my experience laying workers usually develop after a colony experiences a protracted period when it is totally broodless i.e. no eggs, larvae or pupae.

Let’s move on.

3:5:13

If the queen is laying at a steady rate i.e. the same number of eggs per day, then the ratio of eggs to larvae to sealed brood will be about 3:5:13.

This means for every egg present you should expect to find just less than two larvae and slightly more than four capped worker cells.

I’m not suggesting you count them, but you should be able to judge the approximate proportions of the three brood types during your inspections.

This is more complicated than it sounds (and it already sounds quite complicated). The queen lays eggs in an expanding 3D rugby-ball shaped space – the ellipsoid broodnest – moving from frame to frame. Consequently, individual frames will contain different proportions of eggs, larvae and capped pupae, but the overall proportions should work out to be about 3:5:13.

And this is where things start to get a little more interesting 6.

A picture is worth a thousand words

I’ve drawn some simple Excel charts to illustrate some of the points I want to make. For each of the charts I’ve assumed the queen lays at 1000 eggs per day for the first 5 days and then she either stops altogether (perhaps one of those ’quick-but-entirely-unnecessary-and-frankly-idiotic-peek’ queen-meets-Hoffman-frame scenarios), or either speeds up or slows down her laying rate by 200 eggs per day.

The numbers don’t matter, just focus on the proportions of different classes of brood.

Speeding up

If there are more eggs and larvae expected – when compared to the levels of capped brood – then the laying rate of the queen is increasing. For example, here is what happens when she increases her laying rate from 1000 to 2000 eggs/day over 5 days.

Queen increasing her laying rate

The line graph is perhaps less clear than a simple plot of the percentages of the three types of brood. Note the relative reduction in capped brood (pupae) around day 15.

Changes in percentages of brood as queen increases her laying rate

If this occurs it means that the colony has the resources – pollen and nectar – to expand and that you’ll have more young adult workers in another fortnight or so, and an increased foraging force in 4-5 weeks. These things are important if you are thinking about the ability to exploit a summer nectar flow, or perhaps to rear queens in the colony.

Slowing down

Conversely, if eggs and larvae are much less than about 40% of the total brood 7, then the queen is reducing her laying rate. Perhaps there is a dearth of nectar or pollen? Does the colony have sufficient stores? Do you need to feed – little and often – some thin syrup to stimulate brood rearing?

Queen slowing her laying rate (e.g. prior to swarming)

Or is the colony slimming down the queen in preparation for swarming? Do they have sufficient space? Is the colony backfilling brood cells with nectar?

Changes in percentage of brood as the queen slows her laying rate (e.g. prior to swarming)

Note how 12 days after the Q slows her laying rate (assuming she stops entirely 8 ) then the only things left in the colony is sealed brood.

Queen-meets-Hoffman-frame scenario

This is essentially the same as slowing down, except it all happens more abruptly.

Disappearance of brood after the queen abruptly disappears

If you inadvertently kill the queen the colony very quickly runs out of eggs and larvae. Using the emergency response you would expect the colony to raise queen cells promptly.

Estimating brood area during inspections

I’m not suggesting you count eggs, larvae or sealed brood. Inspections are best when they are relatively non-intrusive. It disturbs the colony, it can agitate the bees and it changes the pheromone concentrations and distribution which control so much of what happens in the hive.

But it is worth learning how to determine whether there is more or less sealed brood than open brood and eggs.

Scientists have developed a number of ways to accurately quantify colony strength and population dynamics.

The classic approach, developed between the 1960’s and 1980’s is termed the Liebefeld Method and was nicely reviewed by Ben Dainat and colleagues in a recent paper in Apidologie 9. More recent strategies include the use of digital photography and image analysis, either using ImageJ or semi-automated python scripts such as CombCount.

But none of those approaches are really practical during a normal colony inspection.

I guesstimate the relative proportions of eggs + larvae and sealed brood, and also try and work out the approximate total levels of BIAS present in the colony.

If about 60% of the brood is sealed and there are 3 full frames and about 6 half frames of brood in all stages I would be happy that the colony was queenright, that the laying rate of the queen was probably stable and I’d record the total levels of BIAS as 6 (full frames in total).

Eyeballing sealed brood levels

When you get a frame like the one below it’s easy to work out how much brood it contains.

That'll do nicely

That’ll do nicely …

It’s as near as makes no difference one full frame (assuming the other side looks similar).

But most frames contain a more or less oval brood pattern, some of which may have already emerged.

Brood frame

In these instances it helps to guesstimate what halves, quarters, eighths look like. Or use the diagrams of brood patches on Dave Cushman’s site to work out the approximate total levels.

It’s also worth remembering that the presence of adult bees on the frames will confound things.

Lots of capped brood … somewhere under all those bees

To properly judges the levels of brood you need to shake the bees off the frames. This adds even more disruption to the inspection and I only ever really do it in two specific situations:

  • when looking for signs of brood disease, such as foulbrood
  • when I have to find every single queen cell in the colony

During normal inspections I work with what I can see … and if I need to see more (eggs, larvae or sealed brood) I gently run the back of my hand over the attached workers, or blow gently on them. Both these methods encourages them to move aside, without the ignominy of being dumped in a writhing heap at the bottom of the brood box.

In conclusion

As described – other than the Liebefeld Method – estimating the amount of brood in all stages (BIAS) is a rather inexact process. However, despite this, it’s a useful exercise that helps you judge the state of the colony, and gives you some insight into what is likely to happen over the next few weeks.

And, let’s face it, anything that gives us a better idea of what to expect is useful 😉


Note

Eagle eyed readers will realise there’s a slight glitch in the numbers graphed above. I realised this as silly o’clock 10 this morning and haven’t had time to go back and butcher the spreadsheet and redraw all the graphs. My error does not fundamentally change the patterns observed, but just alters the percentages slightly. I’ll update them once I’ve had a nap 😉

It makes you go blind

Synopsis: There is a sexual arms race between the queen and the drones she mates with. The queen needs to mate with multiple drones to maximise colony fitness. Conversely, it’s in the interest of individual drones to reduce the number of additional partners who mate with the queen. Recent studies have demonstrated that drones reduce repeat mating flights by impairing the eyesight of the queen. Potential implications of this for practical beekeeping are discussed.

Introduction

Honey bee queens are described as polyandrous 1 because they copulate with multiple drones during one or more mating flights taken shortly after emergence.

These multiple matings are a risky business 2.

It takes longer to mate with multiple drones than it does to mate with one, but this time is minimised by reducing the number of mating flights. Rather than leaving the hive, mating once, returning and then repeating the process, the queen flies some distance to a drone congregation area and copulates with multiple drone before returning to the hive.

Shallow depth of field

One of many …

I’ve discussed the location and locating drone congregation areas previously and the distances the queens and drones respectively fly to reach these (which are different to avoid inbreeding).

Between the queen returning from the mating flight and the onset of egg laying there is a delay of a few days. During this period the queen is storing the sperm from the drones in her spermatheca. These are the sperm storage organs within which sperm stays active for years … a necessity as, after the onset of laying, the queen will not go on any more mating flights.

Perhaps surprisingly, only about 3-5% of the sperm transferred from each drone is stored by the queen.

I hope that makes you wonder why she bothers mating with so many drones … it should.

Polyandry and hyperpolyandry

Just before I explain why she only stores 3-5% of the sperm from each of several drones, rather than storing it all from one twentieth the number (and thereby reducing the risks of longer mating flights) of drones, I need to explain the poly bit of polyandry.

How many drones does the queen mate with?

The usual figures quoted are in the high teens, with a range extending from single digits into the low forties. These numbers are determined using a variety of different techniques, at least some of which are likely to underestimate the actual number of drones.

Marked queen surrounded by a retinue of workers.

Here’s one I made earlier …

Think of it like this, if you have a large population of something – like beekeepers – how many would you have to ‘sample’ to find one called ’David’.

Not many, it’s a common name.

But what about ’Atlas’ or ’Zebedee’?

You’d have to sample a lot more apiarists to find any with these rarer names, though I bet they’re out there somewhere. You might even have to use a different way to screen the population.

And it’s the same when determining the numbers of drones that the queen mates with.

Search and ye shall find – detecting rare patrilines

When you use a method that specifically looks for rare patrilines – essentially genetically distinct offspring fathered by different drones – you can find them. This suggests that the queen probably mates with more than the 15-19 drones usually quoted, and that hyperpolyandry is perhaps a better term to describe the mating behaviour of queen honey bees.

There’s evidence that these very rare patrilines (so-called ‘Royal patrilines’) are preferentially selected when rearing queens under the emergency response.

Colony fitness

So now we’ve defined what the poly in polyandry means … but we still don’t know why the queen risks all those aerial shenanigans to mate with so many different drones.

By mating with multiple drones she ensures that the workers in the colony are genetically diverse. This genetic diversity increases the rather-difficult-to-grasp concept of colony ‘fitness’. In this instance fitness is used to mean a combination of adaptability, resistance to stress or pathogens, increased foraging activity, better overwinter survival etc.

I’ve discussed this concept before and suggest you revisit that post for all the gory details.

The bottom line is that colonies that are headed by queens that are mated with very many drones (50+) produce more brood, have better disease resistance and have many other desirable traits (that benefit both the colony and the beekeeper).

The final piece of this introductory jigsaw I need to mention is that drone sperm is used randomly. It’s not a case of ‘first in, last out’. The 3-5% of sperm stored from each drone is mixed thoroughly in the spermatheca.

This makes sense in light of the comments above about colony fitness. If the sperm were used in batches from each drone you’d have cohorts of young bees being produced that had reduced genetic diversity, thereby potentially compromising colony fitness.

It takes two to tango

But let’s think about the poor drones for a moment.

Drones have two fates (excluding getting eaten by a bee eater); they either die while mating with a queen, or they get turfed out of the hive and starve to death towards the end of the season.

If the drone fails to mate with a queen he’s genetic dead end.

If he does mate with a queen there’s a good probability that the genes he carries will be passed on to the following generation.

There is therefore a lot of competition for the queen in the drone congregation areas (DCA).

The drones, once sexually mature, fly every (suitable) day to several DCAs, one after the other. In addition, they fly relatively short distances from the hive to maximise their time within the DCAs.

Heat map of the landscape used by drones – bright spots are DCA’s

This competition is intense, and it doesn’t stop once the drone has mated (and died).

If a queen mates with a relatively small number of drones – let’s say 10 for the sake of argument – the chance of the sperm from any one of those drones being used to fertilise an egg is much greater than if the queen had mated with 50 drones.

The fewer drones the queen mates with the better the chances that the genes from any one of her successful suitors will be passed on to the following generation.

Paradoxically, it therefore benefits the drone 3, if the queen mates with fewer other drones.

And, remarkably, drones have evolved a way to reduce the number of additional drones that a queen mates with.

A sexual arms race

Before I describe the mechanism, it’s worth emphasising here that best interests of the colony are served by the queen mating with many drones, but those of the drones are best achieved by limiting the polyandrous activity of the queen.

These two processes are therefore in direct competition.

There are some additional subtleties.

If the drone simply prevented the queen from mating again 4 it would be detrimental if that drone was the first with which the queen mated. The resulting colony would have little genetic resilience and would be unlikely to survive.

Any one drone must therefore allow the queen to mate with sufficient other drones to ensure colony fitness.

In addition, the more mating flights that a queen goes on, the greater the chances she will be predated by a passing bird, or get lost on the return flight.

From the drones point of view it would probably be beneficial for the queen to go on only one mating flight, but that she mates with sufficient (but no more than that) drones on that flight.

And finally, before I get to the mechanism by which all this is achieved – a compromise solution, like all the best solutions – I’ll remind you that studies have shown that queens go on about 5 mating flights spread over 3, usually successive, days.

Love is blind

At least, too much love is … 😉

Liberti and colleagues have recently published a snappily titled paper on how drones reduce the number of mating flights taken by a queen. The paper is Open Access so you can get all of the nitty-gritty details I don’t have time, energy or intelligence to include in the summary below.

The paper is:

Seminal fluid compromises visual perception in honeybee queens reducing their survival during additional mating flights by Joanito Liberti et al., (2019) eLife 2019;8:e45009

As with all science, the results published in this paper were a continuation of earlier studies of queen honey bees. In particular, these included studies by some of the same authors who had showed that seminal fluid contained proteins that had the ability to interact with neurons.

In addition, in Drosophila melanogaster (the fruit fly, and genetically best studied insect) there was evidence to suggest that seminal fluid promotes fast oviposition and reduces the willingness of females to seek additional copulations.

Drosophila mating in captivity

Now, Drosophila mating behaviour is very different to that of honey bees, but there was clearly a precedent here in which some of the components of seminal fluid – the ‘carrier’ that keeps sperm alive and motile and protects against pathogens – influenced subsequent mating in insects.

Or the lack of mating.

The study by Liberti et al., involves an elegant combination of hardcore molecular gene expression analysis coupled with electroretinography 5 and field work. I’ll skip briefly through the first two of these and provide a bit more detail on the last.

Analysis of gene expression

Virgin queen bees were instrumentally inseminated with seminal fluid (i.e. no sperm) or a control saline solution. Subsequent analysis of the brains of the bees – using a method called RNA-Seq which allows the qualitative and quantitative changes in gene expression to be accurately determined – demonstrated reproducible changes in the gene expression of dozens of genes.

Venn diagram of differential gene expression in instrumentally inseminated queen bees

Detailed analysis of which genes had changed in expression showed that several so-called signalling and metabolic cascades were modified in response to seminal fluid, and many of these mapped to the phototransduction pathways i.e. those involved in sight.

Several of the genes that were detected encoded proteins that were implicated in the conversion of light into the electrical signals in photosensitive electrical cells.

Inevitably, that one sentence has probably confused half the readers that have persevered to this point in the post …

Essentially what this means is that there are components within drone seminal fluid that change the ability of the queen to perceive light, or to see.

So, do they?

Visual perception of queens

The gene expression studies in this paper are complicated (for a molecular biologist). The electroretinography is an order of magnitude more complicated for this molecular biologist to understand … but here goes.

Electroretinography involves measuring the electrical signals generated by particular neurones that are connected to the compound eyes and ocelli 6. This allows the consequences of the changes in gene expression to be determined in terms of the vision of the queen bee.

These studies showed that queens instrumentally inseminated with seminal fluid had lower responses to low frequency flickering light, and that that this response (or lack of response) increased on the second day after insemination.

There were additional changes in the response of the ocelli in queens inseminated with seminal fluid.

Taken together, these results show that queens exposed to seminal fluid experience reduced visual performance.

They are not blinded, but their vision is impaired.

Does this visual impairment have any influence on their mating behaviour?

Mating flight behaviour

Finally, we come to something that’s a bit easier to comprehend, not least because I’ve previously discussed the technology used – the RFID tagging of individual bees to monitor their flight frequency and duration.

RFID-tagged queens (34 in total) were instrumentally inseminated (either mock, or seminal fluid or semen) and subsequently monitored when going on mating flights. Those receiving either seminal fluid or semen were more likely to get lost on these flights, and repeatedly triggered the hive entrance sensors, suggesting they were disorientated by sunlight after leaving the hive.

Of the 21 queens that returned, 81% went on mating flights of more than 7 minutes which was considered a conservative threshold for a completed mating flight i.e. flight to a DCA, mating(s) and return to the hive, and about 50% laid worker brood.

Notably, of the 17 queens that went on ‘successful’ (by duration, not necessarily by outcome) mating flights, those receiving the control saline solution left 1-2 days later than those that had received seminal fluid or semen.

Seminal fluid and semen induce alterations of mating flight behaviour in honeybee queens

These results show that exposure to seminal fluid induces significant changes in queen mating flight behaviour, presumably as a consequence of the alteration to the vision of the queen.

Therefore, the implication from these results is that proteins in the seminal fluid of drones impairs the visual perception of queens, thereby reducing the likelihood that the queen will embark on additional mating flights.

Queens that had already mated (or been instrumentally inseminated in this study) were more likely to get lost on subsequent mating flights, and embarked on these flights earlier.

But what about swarming?

The hive – or a natural nest site – is a low-luminance environment. Queens do not need fully functional eyesight once they have returned from their mating flights. In the hive communication is non-visual, mediated by pheromones, contact, vibrations and sound.

However, although a queen only goes on a few mating flights, she will also leave the colony if it swarms.

Swarm of bees

Swarm of bees

What are the implications for the this study on the eyesight of queens during swarming?

This isn’t really discussed in the paper, but I think there are two likely scenarios:

  • the changes in visual perception by the queen are transient and return to ‘normal’ after a few days, weeks or months
  • swarming is a fundamentally different activity in which thousand of bees leave the hive and for which accurate vision is not needed by the queen.

There’s a world of difference between embarking alone on a mating flight of several kilometres and having to return to the exactly the same location, and leaving on a one-way trip with a swirling mass of attendees with dozens of scout bees leading the way.

Further studies will be needed to determine whether the changes in vision are transient or permanent, as well as to identify the ‘active ingredient’ in seminal fluid that is responsible for the degradation of the mated queen’s vision.

I also think further studies will be required to determine the relationship between dose and timing of the response.

How long does it take for the reduction in visual perception? If the first and second mating flight are taken on successive days is the “return rate” greater than if they are taken a few days apart?

How many drone matings are needed to reduce the visual acuity of the queen? I would predict that this would be a number consistent with the lower estimates of polyandrous matings needed to generate fitness in the resulting colony.

And implications for practical beekeeping?

Perhaps none directly, though I’m interested in the answers to the questions I posed in the paragraphs above.

In an area with low drone densities and those with shall we say ‘variable’ weather – such as my apiaries on the west coast of Scotland (or for that matter, any beekeepers living in remote northerly areas with just a few hives) – is colony fitness compromised by reduced matings?

An isolated apiary

Conversely, is mating success lower because more queens fail to return from subsequent mating flights that they have to take to try and mate with enough drones?

Can mating success and colony fitness be increased by boosting drone numbers?
And is this achievable at a scale meaningful to a small-scale beekeeper?

If a measurable increase in mating success took a 1000-fold increase in drone numbers it’s probably not achievable.

However, if all it took was an extra frame of drone comb in every hive in the apiary, then that’s quick win.


 

Battlefield bees

Synopsis: For millennia bees were used as weapons of war. They are now being developed as ‘weapons of peace’ to help clear the millions of anti-personnel mines left after active conflict ends. Their legendary scent detection abilities combined with high-tech ‘bee detection’ methods show promise and may help reduce the thousands of civilian casualties that occur decades after the war ends.

Introduction

The weekly posts on this website are about bees and beekeeping.

In the same way that I deliberately shun sponsorship and avoid advertising 1 I also try and avoid politics, law and other divisive subjects. These cause enough problems without adding my opinions into the mix … and worse, having to moderate the opinions of others in the subsequent comments.

So, although I might write about the detrimental effects of thiamethoxam on bees, I would focus on the science of neurotoxins rather than politics of lifting the ban of the use of this neonicotinoid in the UK .

It is harmful to bees, but the aphid-transmitted yellows viruses may otherwise decimate our sugar beet crop, and might not the alternative pesticides be more harmful to bees?

Do we even need that much sugar beet?

And what about the livelihoods involved?

You can see how quickly it gets very messy.

But, at the same time, I strive to make posts relevant and even topical. When viewed retrospectively – even if just by me – the posts represent a snapshot of my jumbled thoughts of what’s current at the time.

There are ageing posts on oxalic acid treatment that don’t reference ApiBioxal (the good old days as I like to call them), and others that make passing mention of maximising the oil seed rape (OSR) crop, or processing OSR honey 2.

All of which means I cannot really avoid mentioning the recent Russian invasion of Ukraine 3.

Six-legged soldiers and one-legged civilians

Two years ago I wrote a post about the use of bees in warfare. For many hundreds of years they were an effective tactical weapon to be dropped on or fired at the enemy.

Not individually – that would be just silly – but a hive at a time.

I’ve been present when someone has dropped a full brood box. The whirling cloud of angry bees was reminiscent in shape, though nothing else, to the mushroom-shaped cloud over Hiroshima. Lots of people got stung in the training apiary during that session.

Unfortunately, the ingenuity of man knows no bounds when it comes to killing and maiming others.

The thermobaric weapons employed today are very different from the torsion-powered ballista siege engines used by the Ancient Greeks over two millennia ago 4.

Soldiers now wear carbon and kevlar rather than Corinthian helmets and short-sleeved tunics.

Although you can buy a camouflaged bee suit, it’s not designed for the battlefield, and is likely to be about as much use as the hoodies, jeans and T-shirts that the innocent civilians inevitably caught up – or deliberately targeted – in today’s wars are wearing.

The legacy of war

And long after the battle has ended – years or even decades later – those surviving civilians continue to be maimed and killed by unexploded ordinance and, particularly, by anti-personnel mines.

Minefield sign, Cyprus

So, rather than dwell on the horrors of the present – which is about as far removed from beekeeping as it’s possible to get – I’m going to discuss some more hopeful stories of how bees might help reduce the deaths and injuries caused by anti-personnel mines.

Those readers expecting the (un)usual humour may be disappointed this week … this is not a topic that lends itself well to jokes.

The solutions that scientists are developing to detect anti-personnel mines use a clever combination of the truly awesome scent detection capabilities of honey bees coupled with some very clever technology.

The problem

In 2021 there were 61 countries which were ‘contaminated’ with anti-personnel mines. These mines are typically produced for a few dollars, are perhaps 30 cm in diameter and are buried just sub-surface … and often forgotten.

One definition of the word minefield is ‘a situation or subject presenting unseen hazards’. The plural hazards, and use of ‘field’, indicate that lots of anti-personnel mines are usually buried across an area, thereby rendering it too dangerous to enter.

Farming, trade and communication is inhibited as people have to avoid the minefield(s) … and, if they don’t then the consequences can be devastating.

The International Campaign to Ban Landmines recorded over 7,000 casualties in 2020, 2,500 of whom were killed.

80% of these casualties were civilians and – where the age was known – over 50% of the casualties were children.

Aside from banning the use of anti-personnel mines in the first place, a priority must therefore be to find and removes mines from these areas.

Typically this involves using metal detectors or sniffer dogs for detection, followed by manual clearance. Inevitably, there are considerable risks involved in both the detection and – to a lesser extent – the clearance. These risks make the process time-consuming and expensive.

Which is where honey bees come in …

”I love the smell of Napalm in the morning”

So said Lieutenant Colonel Kilgore (Robert Duvall) in the film Apocalypse Now.

Landmines don’t contain Napalm, but about 90% if them contain TNT (trinitrotoluene).

And not only does TNT have an odour, but landmines continue to emit this odour for years after they have been buried. On a calm day there are vapour plumes of TNT above each of the buried mines 5.

The vapour concentration of TNT is measured in parts per trillion (pptr) and is usually in the range 0.01 – 100 pptr.

Just as the usual way to express areas is by comparison to Wales 6, the ‘volume comparison’ is typically made to an Olympic swimming pool.

1 part per trillion is about the same as half a teaspoon added to an Olympic swimming pool. Not very concentrated …

… but well within the detection capabilities of honey bees. For comparison, this is similar to that of sniffer dogs 7.

To cut a long story short, scientists 8 trained bees to feed on syrup laced with trace quantities of TNT. They then tested the ability of these bees to detect targets emitting field-realistic amounts of TNT.

The results were very encouraging. 97-99% of targets were detected with 1-2.5% of false-positives.

More importantly, the false-negatives (targets that were missed) were less than 1%. It’s much more important to not miss any than to ‘find’ some that aren’t there.

Lidar

The authors neatly sum up the benefits and principles of the study:

Bees do not cause mines to explode, do not require a handler, and can be trained more rapidly than dogs. This technique makes use of the natural foraging behavior of bees, which frequently cover ranges up to several km around a hive. The bees identify the sample location by their increased dwell time while flying in its vicinity.

And it’s that last sentence that should give you pause for thought.

How do you detect the “increased dwell time” – a fancy term meaning spending more time flying in one small area than the remainder of the study area – if you’re trying to find mines in an area about the size of a couple of football pitches 9.

Remember, as if you’d forgotten, you cannot enter the minefield because of those unseen hazards that are lurking just under the surface waiting to blow your legs off.

Bees are pretty small. I can see them against the clear blue sky at 20-30 metres range, but I can’t see them against mixed foliage at anything like that distance.

One potential solution is light detection and ranging (lidar) technology. Essentially this involves shining a scanning laser across an area and detecting the light scattered when it ‘hits’ objects – such as flying bees 10. For additional discrimination, changes in the polarisation of the scattered light has been used to distinguish between bees and what the scientists termed ‘clutter’, which I take to mean foliage.

And it works.

Lidar detection of bees; a) bee heatmap, b) chemical detection (5 is a false positive), and c) visual mapping of bees.

Not only in theory but also in practice … lidar has been used to detect bees detecting mines in an active ‘minefield’. Mines were buried in known locations, trained bees were released and their ‘dwell times’ were recorded using lidar (with the detector about 80 metres away).

Football fields and minefields

But there’s a problem.

Lidar involves a laser scanning horizontally 30-60 cm above the ground. Anything lower than this and the foliage prevents accurate (or any) detection of the bees.

And, even though a minefield might be the size of a football field, it doesn’t look like a football field … either when mined in the first place and definitely not after a few years.

Minefield in the Golan Heights

Unfortunately, there’s also an additional problem.

Tragically the sign above was probably erected after someone inadvertently stepped on a mine. Until that fateful day it might have just been ‘that scrubby bit of field bordering the river’.

Detecting the location of mines in a minefield is one problem.

Detecting whether a field is a minefield is a different – albeit related – problem.

And it turns out that bees might be able to help us discriminate between minefields and football fields, or any other sort of equally harmless fields.

I’ll discuss this before returning to the detection of individual mines in a minefield.

REST (and be thankful)

REST is an acronym for Remote Explosive Accent Tracing 11 .

Since those buried anti-personnel and landmines give off a vapour plume of TNT there are methods of sampling the air and testing it for the presence of trace amounts of explosives.

The ‘sampling’ is highly technical and outside the scope of this post 12.

The ‘testing’ involves sniffer dogs and lots of doggy treat-type rewards. Consequently it is a time-consuming and therefore costly procedure.

However, honey bees are covered in tiny hairs. Through electrostatic interactions, these pick up molecules while they are out foraging. Graham Turnbull 13 and colleagues have shown that flying bees can pick up molecules of TNT (from buried mines) which can subsequently be detected.

The bees are therefore used for wide area sampling, but how is the TNT detected? Graham is a physicist whose speciality is organic semiconductor sensing films … essentially thin films that change fluorescence when certain chemicals are deposited on their surface.

The hive entrances were modified so that the bees passed through a tube. This was made of a special material to pick up – and since lots of bees were making the trips, to also concentrate – the molecules that adhered to their hairs whilst out foraging.

Quenched photoluminescence (red bars) compared to negative control areas (black line)

To cut another long story short, the concentrated molecules were then transferred to the semiconductor sensing film and the photoluminescence quantified. A reduction in the photoluminescence (quenching) was indicative of TNT detection 14.

So honey bees can be used to discriminate between minefields and, er, other fields.

Detecting mines not minefields

I should add that the bees used in the study above were not trained 15 in any way. They simply placed feeders on the opposite side of the uncontaminated test or mined field to encourage them to sample in a reasonably defined area. The bees were not searching for mines, or the TNT vapour plumes, they were just flying back and forth ‘doing their stuff’ and foraging.

Bees are fast learners and can – as described briefly above – readily be trained to associated particular scents (such as TNT) with rewards (i.e. syrup). When you release these trained bees into an area with TNT vapour plumes they home in on these looking for the rewards … and hence exhibit those previously mentioned ’increased dwell times’ near buried mines.

But there’s still the problem of how the bees can be detected.

Huge advances have been made in unmanned aerial vehicles (UAV’s or drones), GPS and video technology in the 15+ years since the original use of lidar to detect bees detecting landmines.

The combination of these technologies now provides a way to detect individual bees, and consequently anti-personnel mines, within an area.

Using drones to monitor bees

A drone flying 10 m above the minefield 16 was used to record high resolution video from which the locations of individual bees could be (computationally) determined.

By detecting bees on individual frames (from video taken at 45 fps), rather than tracking each bee, it was (again computationally) relatively straightforward 17 to generate spatial density maps showing where the bees preferentially concentrated.

Video stills (left) and bee location heat maps (right). The blue circles show mine locations. Bee numbers on scale.

The accurate spatial location was ensured by using a modification (RTK) to GPS which involved an additional ground base station. This increased the standard GPS resolution to provide a horizontal accuracy of 5 cm. The bright coloured foci of ‘increased dwell times’ were less than 0.5 x 0.5 m.

Conclusions and problems

These studies are encouraging. They suggest that a biohybrid system 18, combining advanced physics and area-wide sampling of bees, with the exquisite scent detection of trained foragers coupled with highly accurate video monitoring, might help reduce the number of victims of landmines that occur long after the original conflict ended.

However, there are a few problems that remain to be resolved.

Bees learn fast, but they also forget fast. The authors developed some reinforcement training exercises to ‘remind’ them that they were searching for things scented with TNT.

Bees are not ideal chemical biosensors. They are potentially easily distracted by a strong nearby nectar flow, they don’t forage 19 in poor weather and their availability might be seasonal, depending upon the latitude.

Drones have limited flight times and long vegetation still impedes accurate video detection. Either the bees fly at lower altitudes or the foliage is disturbed by rotor downwash and so increases background noise.

Nevertheless, the expected costs and time involved in both the wide-area sampling and mine detection are lower, and the mine detection per se is much safer.

The mines still have to be destroyed, but knowing precisely where they are – and where they are not – is much more than half the battle … in solving the lethal legacy of a possibly long-forgotten battle.


 

Queen mating flights

Synopsis: How far does a queen fly to mate? Studies using RFID-tagged queens are providing insights into the frequency, duration and temperature dependence of queen mating flights … all of which have practical implications for beekeeping.

Introduction

Although it tends to be a rather poor topic of conversation at dinner parties 1, I’m getting increasingly interested in the mating biology of honey bees. This is an essential part of the life cycle of our bees, and one that has been – and continues to be – well studied.

Marked queen surrounded by a retinue of workers.

Here’s one I made earlier …

When I lived in the Midlands there were a seemingly endless supply of bees in the area. Beebase reported that there were about 200 other apiaries within 10 km of my main apiary. Assuming an average of 5 hives per apiary 2, and ignoring any wild or feral colonies, that’s 1000 hives producing drones with which the queen could mate 3.

Of course, it’s not quite that simple, but bear with me.

In Fife, on the east coast of Scotland, my apiaries are in areas with about 35-40 other apiaries within 10 km, so – using similarly dodgy maths – perhaps 200 hives.

Nevertheless, bees are in apparently plentiful supply.

What do I mean by ‘plentiful’?

As a beekeeper, the two main ways – other than Beebase or by physically searching for them – I can judge the numbers of bees in the environment are, the:

  • success of my bait hives in attracting swarms 4, and
  • the ease with which my queens get mated

If I catch lots of swarms and a high percentage of my queens mate successfully then there must be a lot of bees about.

Apiary density

I was intending to start this post with a discussion of the evenness or otherwise of the distribution of apiaries within the Beebase-defined 10 km radius.

However, it turns out 5 that my maths are not good enough to plot a truly even distribution of hives/apiaries 6. Anyway, common sense dictates that apiaries are not evenly distributed … so let’s instead just consider the number of hives per square kilometre within that Beebase 10 km boundary.

Neighbouring apiaries, hive density and queen mating distances (see text for details)

In the diagram above the enclosing black circle indicates the area within which Beebase reports ‘neighbouring’ (i.e. within 10 km) apiaries. Inside that I’ve shown just four of the 314 one km2 blocks (in blue). On average, in the Midlands each of these would contain ~3.2 managed hives 7. In Fife, there would be – on average again – about 5 times fewer hives per blue square.

Several studies suggest that drones fly relatively short distances from the hive to the drone congregation areas (DCA) where they loiter with intent’ (of finding a virgin queen to mate with). I’ve discussed the use of harmonic radar tracking studies to identify these locations.

So, how many of these hives are actually within the range of a queen on a mating flight?

Where do you go to my lovely?

I posed the question How many of these hives … ? as we don’t know where the actual DCAs are.

The radar mapping study identified several within a few hundred metres of three drone producing colonies, so it seems reasonable to simply assume the DCAs are near the hives, and we know the average density of these.

Harmonic radar tracking of tagged queens visiting DCAs was not successful. It’s a short range technique, and the queen is known to sometimes fly long distances to visit DCAs.

I’ve discussed some of the studies used to determine these long-distance virgin queen flights, but summarise them again here:

  • In studies almost 90 years ago, Klatt observed successful mating on an isolated peninsula when the queen and drones were 6.3 miles (10.1 km) apart
  • In the mid-50’s Peer 8 demonstrated matings could occur when the queen and drones were 10.1 miles (>16 km) apart
  • Jensen 9 demonstrated mating when the queen and drones were 9.3 miles (15 km) apart

Of course, in all these studies it was not determined whether the queen and drones flew similar distances to the DCA. Since we know that drones probably fly relatively short distances it’s likely that the queen does the majority of the leg wing-work.

Ignore the outliers

The Peer studies showed that, although mating could occur when drones and queens were very widely separated, there was an inverse relationship between mating success and distance.

Just because 5% 10 of queens can mate following combined flight distances of 15 km does not mean that’s the distance they usually travel.

Actually, if only 5% of queens get mated at that distance then we can be pretty sure they usually fly much shorter distances.

Fortunately, Jensen did a more thorough analysis of this and showed that 90% of all matings occurred within 4.6 miles (7.4 km) and 50% within 1.5 miles (2.4 km).

And those are the 50% and 90% circles plotted on the diagram above, encompassing an area of 18 km2 and 174 km2 respectively.

Or, to express that area in potential drone donor colonies, 58 or 548 respectively in the Midlands, with a hive density of 3.2/km2 11.

So, in areas with reasonable densities of bees, knowing the majority of queens fly no more than 7.4 km, there are potentially hundreds of colonies producing drones that the queen could mate with.

All of which is a rambling introduction to looking at queen mating distances using a different approach.

Rather than work out how far she flies, what happens if we measure how long she takes?

If we know how fast the queen can fly we can again calculate distances and the number of potential drone producing colonies within range.

Time and weather dependence

But there are additional advantages of looking at queen mating flight duration.

If we can do it accurately we can also determine the:

  1. time of day when most mating flights take place,
  2. influence of the weather on the duration and frequency of queen mating flights,
  3. number of orientation and mating flights the queen takes.

And frankly, as a practical beekeeper, I’m much more interested in the first two of these than I am in the absolute distance she flies for her dalliances.

In an area well-populated with hives, understanding when the queen is likely to be away on a mating flight will help me avoid interrupting her return, and determining when she is likely to start laying.

But, as a scientist, I’m also really interested in the third point as there is some interesting recent work to suggest that drones try and restrict queens taking multiple mating flights 12.

Heidinger et al., studied the mating behaviour of queens using radio frequency identification (RFID) tags 13. Although the study produced no dramatically new results, it was a neat application of technology and allows me to discuss when mating flights occur and the influence of the weather in a little more detail.

The paper is Open Access if you’d like to read it. I’m not going to go through every subtle wrinkle and nuanced argument in the study, but will instead just focus on the important ’take home message(s)’.

RFID tagged queens

This is something I don’t need to discuss in anything other than cursory detail as I wrote about it three weeks ago in ’Chips with everything’.

Or perhaps I do? The post was only read by about 25% of the visitors who read the following week’s ’What they don’t tell you’ … it’s almost as though the hardcore science is less interesting than anecdotes about starting beekeeping. Surely not?

Essentially you stick a unique tag onto a bee and record when it enters or exits a hive using a sensitive reader at the hive entrance.

RFID tagged bees and RFID readers on a feeder

You don’t need to stand by the hive and watch anything.

All the ‘observations’ are made automagically and recorded digitally for subsequent analysis. You can therefore monitor hundreds of workers or dozens of queens simultaneously, thereby increasing the statistical robustness of the results obtained.

The Heidinger et al., study monitored the mating flights of 64 queens.

Of these, 11 were ‘missing in action’ 14 and never returned to the mating nuc.

Fifty three (83% … a figure very close to that quoted above from completely different studies) mated successfully and started laying eggs. However, two of these managed to get out and mate successfully without ever being detected by the RFID reader, meaning that flight times, frequencies and durations are from 51 queens 15.

The study was conducted in two apiaries about 4 km apart in Middle-Thuringia, Germany, in June/July.

Logistics and data wrangling

Conducting these types of field studies is not straightforward. Queens have to be produced in batches and then introduced to mating nucs.

A week of bad weather means the queens will have aged before they have a chance to fly.

What do you do about queens that return from a mating flight but that cluster underneath the mating nuc, only entering (and triggering the reader) after an hour or two?

To accommodate these vagaries the authors:

  • grouped queens according to age,
  • considered flights less than 3 minutes long as orientation flights
  • ignored mating flights of longer than one hour

And whatever filtered through from that pre-screening was then subjected to rigorous statistical analysis.

Time and duration of mating flights

Queens went on mating flights for 1 to 5 days, with an average of 2.2 +/- 0.98 day 16. In easier-to-comprehend terms this means that about 70% of all the queens went on mating flights on 1 to 3 days.

Since it’s often quoted that queens leave the hive ‘once to mate’ this might be a surprise to some.

Perhaps even more surprising is that queens went on a total of 1 to 16 mating flights, with an average of 5.04 +/- 3.11.

One particularly enthusiastic queen went on 7 mating flights in one day. The very definition of ’hot to trot’.

The timing of queen mating flights

Over 80% of these mating flights took place between 1pm and 4pm. From a practical beekeeping standpoint, by avoiding this period for hive inspections you will significantly reduce the chances of being in the way when a queen returns to a mating nuc.

The duration of mating flights

The average length of a mating flight was a bit less than 18 (17.69 +/- 13.19) minutes. Of approximately 255 mating flights (i.e. flights of 3-60 minutes duration) monitored, about 180 (70%) were of 20 minutes or less.

All of these results are in pretty good agreement with a wealth of literature collected using different methods over the last few decades.

Can we use some of these figures to calculate queen mating flight distance?

Duration x speed = distance

I can find nothing in the literature on the speed at which a queen flies. However, I do know that the escapee virgin queens I try and catch usually fly just too fast 🙁

Let’s assume for the sake of argument that the queen flies at about the same speed as a worker bee. This is usually reported as 25 km/hr unladen and about 17 km/hr when laden with pollen or nectar.

Therefore, a queen mating flight of 20 minutes at 25 km/hr involves flying a total distance of no more than 8.3 km. A 10 minute mating flight at 17 km/hr equates to 2.8 km.

These distances include three components, an inward and outward leg separated by the flight time within the DCA. Your guess is as good as mine as to how long the latter takes 17.

However, not knowing something is the perfect opportunity for some informed speculation (or, as here 18, wild guesswork).

Wildly uninformed guesswork

The queen mates with several drones while in the DCA. Although each mating takes a very short time (seconds) there is competition between the drones while they chase the queen, so she must stay within the DCA for a reasonable period.

Time for another assumption … this time let’s assume that the queen spends one third of the duration of her mating flight within the DCA or 4 minutes, whichever is the shorter 19.

If that were the case, a 10 minute mating flight at 17 km/hr, with a third of the flight time being spent in the DCA, would mean the mating site was just 940 metres from the hive. Conversely, if the queen spent no more than 4 minutes in the DCA during a 20 minute mating flight at 25 km/hr, then the mating site must be 3.33 km from the hive.

Either my guessestimate for the time spent in the DCA is too high (quite possible), or the predicted flight speed of the queen is too low (unlikely to be wildly wrong, she’s not going to rush there at 75 km/hr) … or the typical distances queens travel to a DCA are significantly less than those measured using isolated queen and drone-producing colonies in the studies cited earlier by Jensen, Peer or Klatt (see above).

Relationship of time spent in DCA and potential maximum mating flight distance

The table above shows why I think queens likely spend less than 4 minutes in the DCA. Distances in red are within 2.4 km that Jensen showed 50% of matings occur in, those in yellow are within the 7.4 km that 90% of matings occured in 20.

The influence of the apiary

Let’s stop all this wild guesswork and return to the calming certainties of statistically compelling data 😉

The Heidinger study involved two apiaries separated by a few kilometres. All the data discussed above uses recordings pooled from both apiaries. However, queens in one apiary went on more mating flights than in the other. The difference isn’t huge (5 vs. 4 flights in the first three flight days), but is statistically significant.

Mating flight number (a) in different apiaries, and (b) at different temperatures

The queens are described as ‘sister queens’ and I assume this means they are all reared from larvae from the same mother queen, though this isn’t made explicit. If that is the case, it suggests the geography of the area influences queen mating flight frequency.

I say geography, rather than drone availability, as they also added an additional 47 (!) drone producing colonies near one apiary and observed no influence on queen mating flight characteristics.

Although the number of mating flights the queens went on differed, the duration of the flights did not.

The data start to get a bit more complicated when they considered the age of the queens and the duration of the first, second, third etc. flight … so I’ll skip all that and finally just consider the influence of temperature on mating flights.

Some like it hot

It is regularly stated that virgin queens need calm, sunny afternoons with a temperature exceeding 20°C before embarking on mating flights.

This is somewhat disconcerting for a beekeeper living on the cool/wet/windy – but exceeding beautiful – extremities of the UK.

July rain squalls across Mull, Skye and the Sound of Sleat

In fact, mating flights – by which I mean flights of 3-60 minutes (as no record of successful mating on individual flights was made) – occurred in the Heidinger study between a range of 14°C and 25°C.

In cooler weather, queens tended to take more mating flights (shown in the right hand panel on the graph above). The line is a ‘best fit’ and it’s clear there is quite a bit of variation. However, at 15°C the queens would take about 7 flights, compared to only about 4 flights at 24°C 21.

Unsurprisingly therefore, individual mating flights were of greater duration during warmer weather. Again the ‘best fit’ line is shown together with the variation in the primary data.

Relationship between temperature and individual mating flight duration

I found these last two graphs quite reassuring … there were lots of flights below 20°C.

Geek alert

I’m starting to get a bit obsessed with the weather here on the west coast and installed a weather station last summer. I only have complete records from July, but know we had a total of only 27 days on which the temperature exceeded 20°C from July and September.

August 2021 temperatures in Ardnamurchan

2021 was an outstanding summer here on the west coast.

Next year I’ll have data for the full queen rearing season so hope to understand this aspect of the mating biology of my queens a little better.

Conclusions

I’ve covered a lot of ground in this post … from the how far can she fly to mate? studies of the 1930’s to what appear to be short duration, and therefore relatively local, mating flights of RFID-tagged bees.

Understanding when a queen is likely to go on a mating flight should help you with timing your colony inspections. It should certainly help curb your impatience as you wait for your queens to get mated.

Finally, knowing that she can fly on much cooler days than the widely-cited 20°C gives those of us living in more northerly latitudes some reassurance that our queen rearing efforts are not entirely futile.


Notes

Some figures I meant to quote earlier; if the queen only flies between 940 m and 3.33 km to the DCA (see Duration x speed= distance above), and assuming colony densities of either 0.6/km2 or 3.2/km2 (see Apiary density about 3000 words ago 🙁 ) the number of hives ‘within mating flight range’ are between 1.7 and 111.

Quite a range, so ample opportunity for good numbers of genetically diverse drones, though remember that apiaries are not evenly distributed and DCA’s are variable distances from drone producing colonies.

Treat all of my numbers (and particularly my calculations) with considerable caution.

Chips with everything

Synopsis: How do you accurately measure flight times and durations of hundreds of bees? And why would you want to do this anyway? Using the same technology as Marks and Spencers label stock items, albeit on a smaller scale, it is now possible to monitor thousands of honey bee flights very accurately.

Introduction

As a beekeeper, you’re well aware of the size and appearance of a honey bee. Considering the workers only, they are all pretty much the same size and they all look rather similar.

Yikes … I’m only two sentences into the post and I feel the need to add a couple of interesting caveats:

  • honey bees are unusual (amongst bees) in that there is much less variation in the size of individual workers within the population 1. This might aid the accuracy of the waggle dance … 2
  • however, that size is not constant. For reasons that are not really understood, the size of honey bee workers increases during the season, by a small but significant amount 3

OK, let’s get back on track …

Considering this similarity, how can you tell if and when a particular bee returns to the hive?

For example, if you’re interested in the distance from which a bee can successfully return to the hive.

The obvious thing to do is to mark the bee, in the same way you would mark a queen, with a small coloured spot of paint on the thorax.

Small bees, big numbers, Posca pens

But, returning briefly to that very slight increase in size of honey bees during the season, scientists often need to make multiple repeat observations to get statistically significant results 4. This becomes a problem as Posca only do a limited range of colours … you might be able to label bees with only eight different colours.

Mr Blobby goes beekeeping

Or 64 combinations if you use two colours per bee … or 512 if you use three colours together.

There are problems with this. Firstly, it takes a lot of time to put two or three separate dabs of paint onto the thorax of a worker bee. Secondly, the thorax is a rather small target for a rather fat pen (do you remember your first attempt at queen marking? 😉 ).

One way round this is to add dabs of paint to the abdomen as well, or instead, of the thorax. A bigger target certainly, but there are then issues with ensuring flexibility and not blocking the spiracles and a host of other things, so not ideal.

But, even if you could label a few hundred bees with unique colours, you’d then have to sit next to the hive entrance for hours at a time recording the arrival of blue-green-red (or was that green-red-blue? 5 ).

Not ideal … particularly if you are colourblind.

Actually, almost impossible.

But, thanks to Leon Theremin, the Russian inventor of the eponymous musical instrument and developer of the spookily named listening device “The Thing”, the RFID tag was created.

“The Thing”

The Thing” was a covert listening device hidden in a plaque proudly displayed inside the American ambassador’s Moscow residence for seven years 6. It was a so-called ‘passive cavity resonator’. When energised by a radio signal of the correct frequency (which – surprise, surprise – was transmitted by the Russians) it would pick up sound waves from the room, causing a membrane to vibrate. This vibration could be detected by a receiver (which – you guessed it – the Russians also had) and a decoder, thereby allowing conversations to be heard.

искусный as they say in Russian 7.

RFID tags and honey bees

And, on a somewhat smaller scale, that’s pretty much how radio frequency identification (RFID) works.

There are two components:

  • an RFID tag or chip which is attached to whatever you want to uniquely identify. You’ll be entirely familiar with these are they are often attached to price tags of items in shops (where they are used for stock control). They essentially consist of a microchip and an antenna.
  • an RFID reader which emits the radio signal to activate the tag and then ‘reads’ the information sent back. Typically this information includes a unique serial number 8.

RFID tags can be tiny. Hitachi make one that is 0.0025 mm2 which can store a 38 digit number. That’s smaller than a speck of dust. This brings a whole new set of problems as the antenna is so small that the range is only millimetres.

RFID tagged bees and RFID readers on a feeder

But an RFID chip that is about 2 mm2 is small enough to attach to the thorax of a bee and large enough to be relatively easy to detect … for example, when passing a reader at the hive entrance.

Flying home

How far do bees fly?

I’ve discussed this topic previously in a post titled Sphere of influence. Historically these studies were conducted by observing foraging activity in the badlands of Wyoming (where the bees had to fly miles to find anything), or by decoding the waggle dance to infer distances.

But let’s ask a slightly simpler question.

What is the furthest distance that a bee can successfully return to the hive from?

Just think about the practicalities of the experiment.

You could predict that the further away the bee starts, the less likely it would be to successfully return. In addition, the further away the start point, the longer it would take to return.

You’d therefore need to monitor lots of bees over a long time.

In addition, you’d need to be sure that the bees were not wind assisted, or – conversely – homing activity was similar irrespective of the direction the bee was initially transported.

So, more bees.

Time to chuck away those Posca pens and tag several hundred bees with RFID chips.

In 2011 Mario Pahl and colleagues did just that and published a study on the large scale homing of honey bees 9.

Like all good experiments, the study is elegant and relatively straightforward. The paper is Open Access if you want to read it yourself … or keep reading for the juicy bits.

The key experimental details

Recently returned pollen-laden foragers 10 were captured, tagged with an RFID chip ‘emitting’ a unique serial number, placed in a black box, transported up to 13 km from the hive and released.

The hive entrance was fitted with an RFID receiver and the exact time the bee returned – if she returned 🙁  – was recorded.

Map of the experimental area. Triangles mark release sites. Features discussed in text.

At least 20 bees were released in each of 33 different sites distributed to the north, south, east and west of the hive. The bees were transported to the release sites in black boxes so they could not get any positional information en route.

Anyone who transports bees (or cleared supers containing a few straggles) any distance will be familiar with their behaviour if/when you release escapees from the car. They spiral upwards in widening circles until they disappear from sight.

This is very similar to their behaviour on orientation flights. They are – literally – getting their bearings.

The ‘local’ landscape

It’s worth commenting here about the landscape features around the hive.

The experiment was conducted in Australia and the landscape around the hive was distinctive.

The hive was located 1 km east of Black Mountain (BM on the map above), 5 km north of Red Hill (RH 11 ) and about 4 km west of Mount Ainslie (MA). There was a lake (Lake Burley Griffin, LBG) immediately south of the hive 12.

Panoramic view of the experimental area from the home hive.

There was good forage in the immediate vicinity (within 500 m) of the hive, including the Canberra National Botanic Gardens. The authors therefore thought it “unlikely, but not impossible, that the bees knew the areas beyond the lake, behind BM and beyond MA”.

I counted them all out, and I counted them all back 13

Having released the bees they then decoded the unique tag numbers as the bees arrived back at the hive over the subsequent hours … and days.

The closer the release site, the more likely the bees were recorded returning to the hive. However, the homing rates – the percentage that returned for any given distance – were essentially the same for bees released to the north, south and west.

In these directions, no bees returned when released from much over 6 km distance.

Homing rates. The percentage of bees that successfully returned from distant release points.

In contrast, bees transported up to 11 km east of the hive managed to return successfully.

This was not due to the prevailing wind direction which was from the north-east and about 15 km/hr, and would have therefore probably aided bees initially transported north as well.

Flight speeds

The homing speed – assuming the bees flew in a straight line – was about 25 m/min for bees released to the north, south and west, but significantly higher (35 m/min) for the bees released to the east.

Of course, the bees probably didn’t fly in a straight line 14.

These speeds, when converted are only 1.5 – 2.1 km/hr. Honey bees can fly at up to 30 km/hr, but more typically fly at around half that speed.

At 15 km/hr all of the release sites were within an hour’s flight, indicating that a significant amount of time must have been spent searching for the correct bearing, rather than actually flying along that bearing.

The one exception to these flight times/speeds was for bees released on the opposite side of the lake. In this instance, flight times increased markedly despite the release sites being only 400 m apart. It is suggested that the bees minimised their flight over water by following the shoreline to the shortest crossing point in these instances.

Before moving on to the interpretation of the results it’s worth considering the numbers of bees studied, and the impossibility of doing this type of research without RFID technology.

1073 bees were tagged and released. Of these, a total of 394 returned (36%), though 75 of them (7% of released, 20% of returning) took more than 24 hours to find their way back to the hive.

Even the most dedicated PhD student would not be capable of doing this monitoring without the help of technology.

Why the longer and faster flights from the east? 

Considering it likely that the bees only knew the area within a couple of kilometres of the hive, how could they find their way back from up to 11 km away, an epic journey that took several days?

And why did bees initially transported east return at both a higher rate and a higher speed?

It seems likely that for the short to medium release distances (say <4 km), the bees used the distinctive shape of BH to guide them back to the hive. Since this mountain was immediately adjacent to the home apiary the bees would be familiar with it.

Alternatively, since bees are known to sometimes exploit particular flight lines based upon underlying landscape features, the global landmarks such as BM and MA could guide the bees to the next path segment of the flight line.

That wasn’t the question though … the question was why was it only bees flying from the east that successfully returned from distances up to 11 km away?

Getting their bearings

Bees released east of MA could not ‘see’ the hive-adjacent BM (as MA is in the way). However, the authors suggest that – by flying west towards a high point on the skyline (which initially happened to be the mountain MA) – the bees could then “continue on to BM”, where the familiar local features then lead them home.

Whilst that makes some sense to me, it also makes an assumption that the bees somehow fly up and over 15 MA to get a view of BM. Without that view, what else entices them to fly further west?

Do lots of the bees ‘lost’ returning from the east actually end up expiring during their futile search for a hive immediately to the east of MA? The fact that these successful long journeys took ‘several days’ (the precise times are not indicated for individual bees) indicates that the bees obviously spent a long time searching.

There’s an additional conclusion that can be reached from these long-distance journeys. Not only would time have been spent flying and searching, but the bees would also have had to make refuelling stops. A full crop of syrup is only sufficient to keep a bee flying for 25 minutes, or about 7 km at a typical flight speed of 15 km/hr 16. Therefore, the bees would have had to collect nectar several times on their journey.

So, what’s new?

In all honesty, not a lot.

The purpose of describing this study wasn’t because it unearthed some previously unknown details of the foraging or flight range of honey bees. Rather it was to introduce the concepts of uniquely tagged individual queen bees and using automated ‘readers’ to detect their movements.

It’s similar, but different, from the studies that involve uniquely barcoding bees I’ve described before.

Flight homing distances are considered a good indicator of the maximum potential foraging ranges. The figures determined using RFID-chipped honey bees are in broad agreement with the figures reported in previous analogue studies.

These place honey bees approximately mid-table in the league of ‘bee foraging distances’ … Ceratina smaragdula (a green metallic bee) goes no further than 200 m, whereas the South and Central American orchid bee Euplusia surinamensis boldly travels up to 23 km.

Some of the same authors applied this technique to investigate whether neonicotinoids were detrimental to the foraging behaviour of honey bees 17. At high, but sub-lethal concentrations, foraging activity was reduced and foraging flight times increased. However, at field-relevant nectar and pollen concentrations no adverse effects were observed. This study used RFID readers at both the hive and the feeder to record additional features of the foraging flight that would not have been possible manually.

You’ll realise, from the first full paragraph of this section, that I’d meant to discuss studies on queen bee (orientation and mating) flights. As tends to happen, I got a little distracted by espionage, the first electronic musical instrument, the names of mountains and Posca pens, so the queens will have to wait until another time.


 

Scores on the doors

Conveniently, this final post of the year will be published on the final day of the year. This is an appropriate time to look back over the what’s happened here on The Apiarist … a sort of behind the scenes view of the posts that were popular, the posts that were unloved and the creative writing process that converts a title and a topic on a Tuesday to a perfectly honed essay garbled jumble of words on a Friday.

Precisely because the final post of the year appears on the last day of the year, any stats I mention below will exclude this post. Should 15,000 people read this post late on New Year’s Eve 1 then this page would also make it into the ‘Top of the Posts’ lists.

Hives in the snow

And, in between some of the numbers and comments below there’s likely to be a smattering of beekeeping advice or unanswered questions, just to keep you on your toes.

So … without further ado.

Read all about it

Page views, visitor numbers, those registered for email notifications etc. are all higher this year than last, by ~30%.

Going up … page views and visitor numbers graph since time began

New posts appear on Friday afternoon around 3 pm 2 and tend to get the most views on Friday evening and over the weekend, tailing off through the remainder of the week.

Some posts are then rarely read again. Others go from strength to strength, attracting readers in successive months and years. This longevity depends upon a combination of subject matter and ‘fit’ with current search engine algorithms.

Regular as clockwork

Inevitably, the popular posts are often those on ‘how to’ subjects. Perhaps unsurprisingly, considering this is a beekeeping site, the top posts of the year were all on either swarm control or Varroa management.

Top of the posts

These were the most read posts of the year. Tellingly, only the one in bold first appeared this year:

  1. Queen cells … don’t panic! – a title designed to attract the beginner who, having discovered their first queen cells, is now busy panicking.
  2. The nucleus method – my favoured method of swarm control. Almost idiot proof, this explains why it’s my favoured method of swarm control.
  3. Demaree swarm control – a little bit of history and another swarm control method. What’s not to like?
  4. When to treat – a post that first appeared almost 5 years ago. Most of the relevant information is now included in other posts, or summarised in the more recent – and therefore recommended – Rational Varroa control.
  5. Vertical splits and making increase – another ageing post that, by combining swarm control, making increase, requeening and running out of equipment, has something for everyone. I think this could do with updating and deconvoluting.
  6. Swarm control and elusive queens – a useful method for those who struggle to find queens. More important still is that, for beginners, if they understand WHY it works then they’re well on their way to becoming a beekeeper.
  7. Honey pricing – higher, higher! There’s loads of cheap ‘honey’ flooding the market. You are not competing with it. You have a premium product. Do NOT sell your honey cheaply.
  8. Swarm prevention – something that should have been read before items 1, 2, 3, 5 and 6 in this list … but possibly wasn’t considering it was read fewer times 🙁 3
  9. Pagden’s artificial swarm – the most popular method used by beekeeping associations to completely confuse beginners (see the nucleus method above for an alternative).
  10. Oxalic acid (Api Bioxal) preparation – which is currently the most read post, proving conclusively to me that many more beekeepers need to read Rational Varroa control because many colonies will now be rearing brood (see the photo below).

Together, these 10 posts counted for about 20% of the total traffic this year. The remainder were smeared over the other 448 posts that have appeared since early 2013. 

Biscuit-coloured crumbs on the Varroa tray = brood rearing. 23rd December 2021, Ardnamurchan, Scotland

If you’ve got some spare time, show some love for Seasonal changes which only received a single visitor this year. The late September 2016 post contains a nice picture of an orchid and a bottle of honey beer.

Search and ye shall find

The majority of visitors arrive either in response to the weekly emails announcing new posts 4 or from search engine searches. The latter are nominally a valuable resource, so are not disclosed to those of us who actually write the stuff in the first place (unless we pay Google).

However, the 0.5% of searches that come from other search engines turn up a few interesting terms (my selection from hundreds, and in no particular order):

  • cbpv winter – not usually associated together as this is a virus (chronic bee paralysis virus) that usually damages very strong, crowded hives in the middle of the season.
  • diy Kenyan beehive – not something I’ve ever discussed 5 or know anything about 6.
  • how much income from beekeeping – just a bit less than not enough, but fractionally more than SFA.
  • pointers to successful queen introduction (2006) bickerstaffes honey – a really rather specific search. I wonder whether this site was any help?
  • bee hive in old norse – see ‘diy Kenyan beehives’ above, the same sentiments apply.
  • Как сделать станок для натягивания проволоки на рамки для ульев чертежи – that’s easy … you need one of these.
  • maldives beekeeper – I have one photo on the site from the Maldives which I suspect resulted in this ‘hit’. I hope the reader wasn’t disappointed 7.
  • does a virus make bees angry – actually not such a daft question. There’s a Japanese strain of Deformed wing virus called Kakugo which is supposed to cause aggression. Kakugo means readiness or preparedness.

And, of crsuoe, there wree hrdudens of saehrces wtih snlpileg errors. Mabye smoe brepkeeees olny serach for initofrmaon atfer benig stnug rltedepaey on tiehr fenirgs? 8

Some of the spelling errors were so gross that the resulting word was barely recognisable.

There were also about 8 different spellings for ‘apiarist’ … not bad for an 8 letter word 😉

Prolixity

Fifty two posts have appeared in 2021, each averaging 2,675 words. This is an increase of about 8% over the 2020 figures 9. In total, excluding the ~1200 comments, that’s about 139,000 words.

Tolstoy’s War and Peace … more words, more characters, less bees

For comparison, this is a bit under 25% the length of War and Peace.

Phew!

Talking the talk

As well as writing too much (it has been said that) I talk too much. During 2021 I’ve given 25 talks to beekeeping associations stretching from Cornwall to Inverness 10. Audiences have ranged from about 15 to 350 and I’m very grateful to all the BKA’s who hosted me and coordinated the Q&A sessions.

Particular thanks to the associations that managed to send me the Zoom link for my presentation before the talk was supposed to start 😉 .

Although the talks were all ‘virtual’ it was good to see some old friends and to make new contacts.

Spam, spam, spam

Of the ~1200 comments I mentioned above, many are from me. I try to respond to every comment, irrespective of whether they are corrections (for which many thanks), additional insights (thanks again) or further questions 11.

Running a website, even a relatively low traffic one such as this, means you receive a lot of spam. ‘A lot’ means usually between 200 and 800 comments or emails a day. To avoid the comments section getting tainted with adverts for fake sunglasses or dodgy prescription drugs 12 I manually ‘approve’ every comment that appears.

Spam

This isn’t as onerous as it sounds. I run spam filters that trap the vast majority of the unwanted spam.

This filtering is not 100% accurate … if you previously posted a comment and it never appeared then it may have fallen foul of these filters. Next time avoid mentioning that you were wearing Ray-Ban sunglasses when you inspected the colony 😉

It’s a rather sad indictment of the internet that I sometimes receive the same amount of spam in one day as I receive in valid comments in one year 🙁

You’ve got mail

The comments and questions – whether to posts or talks – are often very interesting. After all, I may have delivered the same talk three times in the last month, but the questions will always be different. I’ve touched on this previously in Questions & Answers.

Some questions are direct, relevant and on-topic. These are usually easy to understand and answer, though they may not be easy to answer correctly.

But there two other types of question:

  • Rambling, incoherent and vague … almost always lacking some essential information, like location. These often start with a detailed description of the last three colony inspections and end with something about Nosema or polycarbonate crownboards. There may not even be a question mark …
  • Direct – verging on blunt – and totally off-topic. It’s not unusual to prepare 2,500 carefully crafted 13 words on rational Varroa control to then receive the question ”What is the recipe for thick syrup?”.

In addition to comments/questions to posts and talks I receive a lot of email. If you emailed me this year and I failed to answer promptly then it’s probably because there were 50 other unanswered emails I’d yet to wade through.

With the volume becoming unmanageable I’ve started ignoring the very terse emails requesting a quick response (because the sender is ‘busy’ and wants the answer before they leave for the apiary/office/school run/anger management class) like “What is the recipe for thick syrup”.

The few who send adverts for their quack solutions to Varroa (often vaguely disguised as informed questions) or abuse – you’d be surprised, I was – are both ignored and blocked.

Life is too short …

New topics and old chestnuts

Beekeeping is a fantastically diverse activity 14. From the single hive owner to huge commercial operations, from the hive-monitoring techno-geeks to the leave-alone organic types, from honey to venom … there really is something for everyone.

It’s therefore no surprise that there is never a shortage of topics to cover. This is particularly true when you also include some of the wonderful 15 science of honey bees.

Web of Science publications on “honey bees” since 1997

I’ve covered some beekeeping topics exhaustively and get little satisfaction from re-writing the same thing differently 16. However, these are the topics that often attract the most readers – presumably many of whom are new beekeepers.

I’m not too fussed about the reader numbers, but if I’m going to go to the trouble of writing something I do want it to be read 17.

I’m currently wondering about how to achieve a balance between what might be considered the ‘basics’ and some of the more advanced – and to me (after a lot of beekeeping) much more interesting – topics.

And I’m always happy to consider new topics if you think I’ve missed something 18.

The writing process

I usually accumulate ideas on long car journeys, while walking in the hills, out on the loch or during interminable meetings. They might start as little more than a title and a reference, or a sentence of text.

Seeking inspiration for new articles for The Apiarist

I rarely have anything actually written by the weekend before the post appears, though I will usually have decided on the topic.

This post is being written on a Tuesday, but late – often very late – on a Thursday is more typical.

Two to four hours is usually sufficient for most posts, though additional time is needed if there are custom figures or graphs.

It’s very useful to then leave the draft for a few hours after ‘finishing’ it.

I usually abandon the keyboard by 2 am on Friday and look again first thing the following morning. Typos are caught, my awful punctuation is largely fixed and some of the more garbled sentences are rewritten in English 19.

And then I press ‘Submit’.

Flat white, cappuccino, ristretto, latte macchiato and affogato

And all of those activities – the thinking, the writing and the proof-reading – are fuelled by a delicious and fulfilling combination of strong coffee and pizza.

I’d therefore like to again thank the supporters who have ‘Bought Me a Coffee’ during 2021. In particular I’d like to acknowledge the repeat supporters. In addition to facilitating my nocturnal writing marathons, this support has also enabled moving the site to a more powerful (and properly backed up and appreciably more expensive) server.

Thank you

The future

I’m looking forward to the year ahead for many reasons. I expect 20 to have a lot more time for my bees and beekeeping. In the meantime, I’ll probably write about some of my immediate plans in the next week or two.

Winter-flowering gorse, December 2021

The size and complexity of this website – hundreds of posts and thousands of images – is starting to make it both difficult and time-consuming to maintain. It’s a dynamic site, the pages being generated on the fly when your web browser requests them. There’s a significant performance cost to retaining these dynamic features, and the underlying software is bloated and a target for hackers.

I’m therefore considering alternatives that make my life a little easier and your browsing experience a little faster. One way to achieve this is to use what is termed a static site. Anyone who has looked up details of my online talks (which has ~16 images and ~2500 words, so broadly comparable to a Friday post) will have used one of these. This technology is becoming increasingly common for blogs. I still need to resolve how to retain the comments/discussion features.

I’m also keen to explore some more expansive topics.

Even ~2500 (or more) words is insufficient to do some subjects justice; the impact of honey bees/beekeeping on solitary bees and other pollinators, neonicotinoids, fake honey, the prospects for Varroa-resistant bees, more advanced methods of queen rearing etc.

Real honey … not the product of unspecified EU and non-EU countries

How do I tackle these?

Should I write less and not explore the subject fully?

Write in instalments?

Or just not bother?

What do you think?

And while you ponder that and some of the other points raised above I’m going to enjoy the last few hours of 2021 and close by wishing all readers of, and contributors to, this site the Very Best for 2022.

May your supers be heavy, your queens fecund, your bees well-tempered and your swarms … from someone else 😉

Happy New Year


Notes

The phrase [the] Scores on the doors originated from the panel show The Generation Game hosted by Larry Grayson between 1978 and 1982. However, it was subsequently appropriated to indicate the public display of food hygiene ratings.

If you arrived here from @Twitter then you might be wondering what omphaloskepsis is. It means navel-gazing as an aid to meditation. Readers with a classical education will recognise its derivation from the Ancient Greek for navel and contemplation. Scrabble players will be disappointed it doesn’t contain more high scoring consonants.

Honeyguides

That’s not a typo.

I didn’t mean Honey Guides … or honey guide.

The sweet spot ...

For once we’ll discuss something else …

Honeyguides are a group of 17 species of birds, distributed into four genera, belonging to the family Indicatoridae. All of the 8 species that have been well studied are brood parasites, like the cuckoo (Cuculus canorus). They lay their eggs in the nest of another species – usually a specific species as they are evolutionarily adapted to match the egg size and shape 1 – and subsequently puncture the other eggs to destroy the developing embryo. 

There’s some great research on the evolutionary arms race between the egg puncturing ability of honeyguides and the eggshell thickness of the host species 2 … but I’ll leave that as your homework for the holidays 3 as I want to discuss something else about honeyguides.

Indicatoridae by name, indicator by nature

The really remarkable thing about honeyguides is hinted at by the family name. 

Indicatoridae

This reflects their ability to lead human honey hunters to a wild honey bee nest site.

Of the 17 species of honeyguides, it is only the greater honeyguide (Indicator indicator) that has been extensively studied for its guiding behaviour. There is disagreement whether the scaly-throated honeyguide also exhibits similar guiding activity.

For the rest of this post, when I say ‘honeyguide’ I mean the greater honeyguide.

The greater honeyguide lives in dry open woodland in sub-Saharan Africa. It is a rather dull-coloured, starling-sized bird. It eats honey bee larvae, pupae and wax from the nest, and is one of the few birds that can digest wax.

honeyguides

Greater honeyguide

However, the honeyguide cannot access most wild honey bee nest sites. These are often in a hollow tree and are well-defended by the bees.

But, over millenia, the honeyguide has learned that honey hunters, who have the benefit of being able to use smoke to calm the bees 4, leave a lot of debris after robbing the nest of honey.

And, over millenia, the honeyguide and honey hunters have evolved a mutualistic relationship in which the bird guides the human to the bee’s nest. The hunter gets the honey (and probably pupae, an important source of protein) and the honeyguide gets the leftovers.

“Mutualism describes the ecological interaction between two or more species where each species has a net benefit.”

Everybody wins 🙂

Guiding behaviour

Greater honeyguides are territorial and scout out the location of wild bee nests in their territory. Each territory may contain multiple honey bee nests.

To attract the attention of a honey hunter the honeyguide emits a distinctive chattering call 5.

 

They then flit from tree to tree, towards the honey bee nest, perching and spreading the tail to expose two conspicuous white spots.

This behaviour was reported as long ago as 1588. João dos Santos, a Portuguese missionary, described the ability of the bird to lead honey hunters to bees’ nests (and also described how the bird would enter the church to eat the wax candles).

Guiding by honeyguides is very effective.

The honey hunters have learned to recognise the distinctive call, flight and perching activity of the bird 6. Studies have shown that ~75% of guiding events lead to the successful identification of at least one nest. 95% of these were honey bees nests and the remainder were stingless bees.

Smoke ’em out

Once the nest has been located the honey hunter uses smoke to calm the bees. Often the nests are located high up in the tree so the hunters attach some smouldering wood to a long pole and hold it near the nest entrance. They can then climb the tree and approach safely.

There are no bee suits or veils used … many of the photographs of honey hunters I’ve seen show them wearing just sandals and shorts.

The entrance is widened with a machete and the honey-laden combs are extracted intact and lowered to the ground … no doubt after a little ‘quality control’.

It’s not just humans who value honey … chimpanzees love the stuff as well, but they eat less than 1% of the honey consumed by humans in the same area. Chimpanzees, although known to use tools, do not know how to exploit fire. They are therefore ineffective honey hunters.

In a multi-year study of chimps in the Kibale National Park, Uganda, about 60% of of bees’ nests were successfully defended by the bees, driving the chimps away by stinging them. In contrast, human honey hunters are never driven away after smoking the nest.

Smoke is the key component needed for successful robbing of the nest by the honey hunters.

Two way communication

So, the honeyguide signals – with calls and its characteristic behaviour – to the honey hunter, guiding them to the nest site. The honey hunter can ‘read’ and understand these signals and can accurately home in on the nest.

But what if you are a honey hunter and, as you start your foraging, there are no honeyguides to be seen or heard?

This is where the close relationship between the honeyguide and the honey hunter becomes even more extraordinary.

The honey hunter calls to attract the honeyguide. 

Not just any call, but a specific call … and to add an additional level of complexity, different tribes use different specific calls to attract honeyguides.

Remember, these are wild birds. 

We’re all used to communicating with domesticated animals … “Here Fido!” 7, but a specific call to attract a wild animal is probably unique.

The Yao honey hunters in Mozambique use a distinct ‘brrrr-hm’ call to summon the honeyguide. 

 

An excellent study by Claire Spottiswoode and colleagues showed that this call, not used by the Yao people for anything else, more than doubled the likelihood of attracting a honeyguide to the honey hunter and initiating guiding by the honeyguide 8. The call successfully attracted a honeyguide about two-thirds of the time it was used.

The characteristic ‘brrrr-hm’ call is passed down the generations of Yao honey hunters – from father to son 9 – meaning that a bird hearing the call could be reasonably certain the caller has the skills and tools necessary to harvest the honey.

Learning the lingo

Not all honey hunters use the same call. The Hadza people of northern Tanzania use a melodious whistle to attract honeyguides. The Kenyan Boran people use a distinctive sharp whistling call.

Different geographic populations of honeyguides clearly recognise distinct calls by the hunters.

How do the birds learn to recognise the call of the honey hunter?

Obviously not from their biological parents.

Remember, these are brood parasites and they are reared by other species such as lesser bee eaters or green woodhoopoes.

And there’s another amazing story here as these hosts have different shaped eggs 10. Different lineages of honeyguide have evolved that lay a suitably shaped egg that matches that of the specific host 11. The host specialisation is thought to reside on the female-specific W chromosome. 

OK … enough digression.

It appears that honeyguides have an innate ability to recognise human calls. As young birds they listen for these calls and learn them, a process presumably reinforced through successful honey hunting in concert with humans.

Whether juvenile Tanzanian honeyguides transported to Kenya or Mozambique could identify the ‘local’ honey hunter’s call has not been tested, but would be interesting. I wouldn’t be surprised if the call used by the honey hunter has not also evolved (the evolution of languages is itself a fascinating area) to be distinctive from other sounds in the particular area, or to carry longer distances … or that is more attractive to the honeyguides.

The evolution of mutualism between humans and honeyguides

How did humans learn to call and follow honeyguides?

Originally it was thought to involve copying the natural guiding by the bird of honey badgers (ratels).

Mellivora capensis – the honey badger.

However, this story has largely been discredited – ratels do not call to attract the honeyguide and there’s a suspicion that videos showing birds guiding badgers have been staged 12.

Instead, it is much more likely that the mutualistic relationship between humans and honeyguides evolved over a very long period.

Since we’re talking about evolutionary timeframes here this could potentially mean millions of years.

Have humans been about that long?

No … we are the ‘new kids on the block’. Homo sapiens evolved from our hominin ancestors about 300,000 years ago. Therefore it’s likely that early hominins such as the (relatively recent) H. heidelbergenesis (0.4 million years ago (Mya) ), H. erectus (1.6 Mya) or H. habilis (2 Mya) were involved instead.

The divergence of humans and great apes from a common ancestor

Have honeyguides been about that long?

Yes … analysis of the mitochondrial DNA (inherited solely from the mother) of those distinct burrow- or tree-nesting lineages of honeyguides demonstrated that they diverged at least 3 million years ago.

Have honey bees been around that long?

Certainly … Apis mellifera probably evolved from other cavity-nesting bees about 6 Mya 13

There’s no smoke without fire

One of the great debates about the evolution of humans is when our ancestors learnt to create and use fire. 

There is good evidence for use of fire about 1 Mya and additional claims that evidence control of fire 1.7 – 2 Mya 14.

All of which provides ample time for the evolution of mutualistic behaviour between H. erectus and the greater honeyguide.

This behaviour cannot have evolved without the ability of early hominins to control fire. The study of chimpanzees failing to successfully and efficiently collect honey shows this must be the case. 

At least 44 distinct African ethnic groups exhibit the type of mutualistic relationship with honeyguides I have described and current studies are aimed at determining when the hominin-honeyguide mutualism evolved 15.

A honey hunting scene at Abrigo de Barranco Gómez in Castellote, Teruel, Spain c. 7500 years old.

The fossil record cannot help us here. There’s also a huge gap between the evolution of the early homonins and the upper Paleolithic rock art that clearly depicts honey hunters smoking bees’ nests.

More studies are needed. However the inexorable passage of time is now accompanied by increasing urbanisation, the availability of refined sugar and exclusion of hunter gatherers from nature reserves. This means that people depend less on honeyguides.

In time I expect it will be inevitable that this wonderful example of interspecies cooperation will be lost.

As another year draws to a close and you spread honey on your breakfast toast, take a moment to marvel at how our ancestors’ love of honey resulted in the evolution of the only known mutually beneficial relationship between a wild bird and humans.

Extraordinary.

Happy Christmas


Notes

There’s a BBC Natural Histories podcast on honeyguides featuring Claire Spottiswoode available online. The programme notes are:

The greater honeyguide is unique: it is the only wild animal that has been proven to selectively interpret human language. Brett Westwood tells the sweet story of a bird that leads human honey hunters to wild bees’ nests in order to share the rewards – perhaps one of the oldest cultural partnerships between humans and other animals on Earth. With biologist Claire Spottiswoode, anthropologist Brian Wood, and honey hunters, Lazaro Hamusikili in Zambia and Orlando Yassene in Mozambique, and the calls of the honeyguide. Producer: Tim Dee.

Science snippets

Three short and easy-to-digest snippets of science this week. After last weeks’ overly-long DIY extravaganza I thought I’d try and be a little more succinct this time. 

The following triptych is based on three separate papers, two published in the last month or two and one from last year. Individually these incremental advances in our understanding probably do not justify a post of their own. 

The first paper, on sodium butyrate, was included here following a question I was asked during an evening talk to a beekeeping association last week. I don’t think I answered the question particularly well, so thought I’d elaborate here for clarity. The science is cool, but the paper is rather odd.

The other two papers are on a related topic, the bacteria in the gut of bees. The first of these came out last week and had a very catchy title. Reading that paper resulted in my burrowing back a year or two into the literature. While doing this I found a related paper that has got me thinking again about feeding winter bees honey, syrup or fondant.

Sodium butyrate reverses DWV-induced memory loss

All honey bees, perhaps with the exception of those in Australia 1, are infected with deformed wing virus (DWV). Historical studies that report 30% or 60% or whatever virus prevalence were probably using an insensitive assay. Even bees in Varroa-free regions carry DWV. 

And, in the absence of Varroa, DWV is not a problem to the bee 2. It is present at low levels and is apparently not pathogenic.

However, when transmitted by Varroa, the virus levels are amplified about a million times are a range of symptoms are clearly present. These include pupal death or the emergence of workers with overt developmental defects, including the classical ‘does what it says on the tin’ deformed wings.

DWV symptoms

DWV symptoms

In laboratory studies up to 70% of the bees exposed to high levels of virus exhibit these catastrophic symptoms.

However, some bees emerge with high levels of virus, but ‘look’ normal.

But they don’t behave normally.

In particular they have defects in memory and learning. 

Forgetfulness and getting lost

Impairments in memory and learning are bad news for bees. 

Foragers need to be able to learn where sources of nectar and pollen are by interpreting the waggle dance. Perhaps more importantly, they need to remember where the hive is so that they can successfully return from a foraging trip. If they forget where they are going, they’re doomed. 

A social insect like a honey bee cannot become a solitary bee without inevitably becoming a dead bee.

There is a long history of using sodium butyrate (NaB) to either enhance memory, or to reverse memory loss. It belongs to a class of compounds called HDACi’s (histone deacetylase inhibitors) which have been used in medical studies including anti-neural degeneration and anti-Alzheimer’s disease. 

NaB has even been used in studies with honey bees. In these it has been shown to enhance expression of genes involved in the immune response, detoxification and learning/memory. 

In addition, NaB restores learning ability in neonicotinoid-treated bees … it was therefore a logical extension (particularly since this neonic study was conducted by the same Taiwanese researchers) to investigate a role for NaB in counteracting DWV-induced learning and memory loss, the topic of the first paper this week 3 .

CCD and ‘massive disappearance’ of bees

This paper is a bit of a curate’s egg. The science is detailed and appears to be done well. The experiments are logical, mostly well-controlled and involve a combination of detailed molecular studies with monitoring bee behaviour in the field. 

However, the attempted link between memory loss and bee loss, the association with CCD (colony collapse disorder) and the superlatives in the paper make for a rather strange reading experience.

I’m not going to give a detailed account of the science. The key points are as follows:

  • NaB increased honey bee survival after oral DWV challenge 4. Disappointingly they did no virus assays.
  • NaB reversed memory loss in the standard proboscis extension assay (PER)
  • Gene expression studies indicated that NaB (an HDACi) resulted in increased expression of numerous genes, including reversing the suppression of some genes caused by DWV infection. Some of these genes were involved in memory, but many other gene classes were also differentially expressed. NaB was also shown to restore some neurotransmitter activity in the brain.
  • Colonies fed NaB and then fed DWV experienced a much reduced loss of bees than those that just received DWV.

Sodium butyrate reverses bee loss due to DWV (A) in/out ratios and (B) lost bee ratios

I need to re-read some of the methods and data on the in/out ratios (the graph on the left above) as it appears that more bees returned to the hive than left the hive! These field experiments used an automated hive monitoring system , but did not apparently use any form of tagging on the bees. It is not clear how they could be certain that the ‘returning’ bees originated from the monitored hive.

Smells fishy?

The conclusions of the paper end with the sentence a diet incorporating histone deacetylase inhibitors could be used to maintain the overall wellbeing of the bees and integrity of the colony”.

Well … perhaps.

I’d argue that prevention is always better than cure.

It is preferable to minimise DWV levels in the hive – by killing Varroa – than it is to try and counteract the deleterious effects of DWV by adding additional chemicals. Studies from my lab and others show that effective Varroa control results in very low virus levels.

But if you are going to feed them HDACi’s, then it probably should not be sodium butyrate. 

The ‘butyrate’ bit of the name is derived from butyrum meaning ‘butter’ in Latin. Sodium butyrate is a fatty acid and is famously smelly. It reeks of spoiled milk, or sour butter, and is the compound that gives vomit that distinctive ‘smell-it-a-mile-off’ odour.

Hmmmm …. nice 🙁

So, although it doesn’t smell fishy … it certainly does smell. 

Possibly not something you’d want anywhere near hives producing honey 😉

Chicken eating bees

I wrote recently about how important catchy titles are to scientific papers. The title of this next paper was the only thing that made me read the study …

Why Did the Bee Eat the Chicken? Symbiont Gain, Loss, and Retention in the Vulture Bee Microbiome by Figuerosa et al., (2021) mBio 12:e02317-21

How could you not want to read a paper with a title like that?

Well, one reason might be that you don’t know the words symbiont or microbiome.

Let’s see if we can change that … 😉

Vulture bees

Honey bees, along with all other bees, are classified with the sawflies, wasps and ants as members of the Hymenoptera. Of these, bees are wasps that switched to a vegetarian lifestyle, eating pollen and nectar.

Vulture bees dining out on chicken

However, some stingless bees also dine on carrion (literally ‘the decaying flesh of dead animals’) and a few species – the aptly named vulture bees – only feed on carrion for protein and no longer collect pollen.

You are what you eat

The microbiome is a collective term for the all the bacteria 5 in a particular environment.

For example, the gut microbiome or the skin microbiome. 

In the gut, these microbes help the host exploit novel food resources. For example, honey bees have bacteria (Gilliamella apicola) that help them digest toxic sugars 6.

The host (bee) benefits from the presence of the bacteria, and the bacteria benefits from the protection and food provided by the host … which is exactly what the term symbiotic means.

You are what you eat is, of course, not meant literally 7.

However, it is certainly true that the symbiotic microbiome is significantly influenced by diet. And the symbiotic microbiome also influences what can be consumed.

The Figuerosa et al., study compared the gut microbiome of a variety of stingless bees from Costa Rica. Some of these bees were pollenivorous and others were facultatively or obligately necrophagous.

Eh?

  • Pollenivorous – pollen eating
  • Facultatively – some of the time 
  • Obligately – all of the time / only
  • Necrophagous – feeding on corpses or carrion

The microbiome of vulture bees

By analysing the microbiome of these different types of bees the authors determined that reversion to a purely necrophagous lifestyle had resulted in the acquisition of a unique range of additional bacterial species.

Gut microbial communities in pollen-eating (absent), or facultatively or obligately necrophagous stingless bees.

However, the gut microbiome was not entirely unique. Many species were also found in facultative necrophagous bees, or in the pollenivorous species. 

It’s not yet clear what all these new species actually ‘do’ in the gut of these carrion eating ‘vulture’ bees. Further studies will be needed to determine this.

And, of course, this study begs the additional question.

Which came first, the chicken or the bacteria? 8

Did the microbiome change in response to a change in diet, or was the change in diet enabled by the change in the microbiome?

And, the topic of changes in the microbiome is the topic of the third paper … which, you’ll be relieved, is on honey bees.

The microbiome of summer and winter bees

I really used the ‘vulture bees’ paper to introduce the concept of the symbiotic microbiome.

In honey bees, the microbiome has been extensively studied over the last decade or so.

A striking feature is that it includes relatively few species of bacteria, and is dominated by less than 10 in total 9. These species are conserved regardless of geography, life stage (nurse bee, forager etc.) or season.

Almost every study of the honey bee microbiome has been a qualitative one. By that I mean the scientists determine the species present, but ignored the quantities of the different bacteria. 

In comparison, a quantitative study would have determined the amounts of some or all of the core species in the microbiome. 

And that is exactly what Kešnerová et al., (2020) did in their study entitled Gut microbiota structure differs between honeybees in winter and summer 10.

Multi-year, multi-hive studies

As you would expect from a paper in the ISME Journal 11 this is a thorough study, involving sampling of one hive on a monthly basis for 24 months, and fourteen hives in two different locations in the summer and winter. Each sampling involved multiple individual bees that were analysed. There are some additional experiments on colonisation of the gut that I’m going to largely ignore here.

The authors qualitatively and quantitatively studied only five of the core species and two non-core species from the gut microbiome. The names don’t really matter, but are shown in the figures below.

The gut microbial community differs between summer foragers and winter bees

There’s a huge amount of date in this figure.

However, simply by looking at the monthly changes (A), or the community composition (B), it is clear that summer foragers and winter bees have significantly different microbial populations within the gut.

In addition, the overall levels of many of the species tested (C) were significantly increased in the winter bees population.

Summer bees, nurse bees and winter bees

From a physiological and dietary point of view, there are some similarities between nurse bees and the long-lived winter bees. The authors therefore tested the bacterial population the gut of each contained in summer (foragers and nurse bees) and winter (winter bees).

Bacterial load and community composition in foragers, nurse and winter bees

Nurse bees and winter bees contained at least 10 times the population of bacteria as present in the gut of foragers (A, above). Of these, nurse bees were intermediate in the range of species between the foragers – which had a greater range – and the winter bees which contained fewer species.

Finally, detailed statistical analysis of the populations in the three bee types indicated that they were distinct (C), despite conservation of several of the core microbiome species. This latter analysis showed that, whilst each was distinct, all of the populations were similarly variable within a particular bee type i.e. none of the dots are more clustered/scattered in the third panel above.

Diet and the microbiome

Numerous studies have shown that diet influences the bacteria in the gut – of honey bees, vulture bees, flies, mice and men. It’s therefore very likely that the diet of nurse and winter bees at least partly accounts for the differences in the bacterial community present in their gut.

Foragers need an energy-rich diet and mainly feed on nectar and honey. In contrast, nurse bees and winter bees also consume pollen.

In studies I don’t have time to discuss, Kešnerová et al., (2020) also showed that feeding gnotobiotic bees 12 pollen and syrup resulted in significant increases in the amount and levels of bacterial colonisation i.e. they resembled nurse or winter bees. In contrast, bees fed syrup alone developed a gut microbiota that resembled that of foragers.

All of which made me think about feeding bees syrup/fondant for the winter vs. feeding/leaving them honey.

Honey is better for bees in the winter … really?

Beekeepers who leave their bees with a super or so of honey are often convinced of the benefits to the colony.

When pressed they unfortunately provide little evidence to support their expensive decision 13

I’m not aware of a single study that convincingly i.e. statistically, demonstrates that colonies are more successfully overwintered on a diet of pure honey, rather than a colony fed syrup or fondant. 

I’ve discussed this before – for example, see my response to this comment in the post entitled ‘Cut more losses’. 

Is the microbiome a marker of colony health?

However, this paper on the winter bee microbiome got me wondering whether – in the absence of evidence supporting better overwintering survival – bees fed syrup/fondant or honey have a different bacterial population.

It would be very interesting if they did.

Furthermore, as scientists further untangle the role of these bacteria, we would be able to tell whether syrup/fondant was better, worse or neutral in terms of the changes it induced in the bacteria that inhabit the winter bee gut.

Unfortunately, the Kešnerová et al., (2020) study has no details whatsoever of the hive management regime. The work was done in Lausanne, Switzerland, but it doesn’t say how or what they were fed for the winter.

Nor is there any mention of whether the diet was supplemented with sodium butyrate 14. This will also need to be studied as butyrate is a natural product of some gut microbes and there is evidence that – in humans at least – it is involved in communication between the gut and the brain.

And I think my gut is telling my brain that it would like some pizza …