Category Archives: Behaviour

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.


 

Dancing in the City

Beekeeping is an increasingly popular pastime. Since ~84% of the UK population live in urban areas (up from ~70% in 1950’s) it is not unsurprising that the number of hives kept in cities is increasing.

Of course, not everyone who lives in a town or city keeps their bees in the back garden. When I lived in the Midlands I lived on a small estate that was indisputably ‘urban’, although there was farmland within sight 1. My bees were on the nearby farmland and I just kept a few mating nucs and a bait hive in the back garden 2

Hive in a field margin

I kept my bees in the farmland because 3 I reasoned that there were both larger amounts and a greater range of forage available for them there.

But I was probably wrong.

It wouldn’t be the first time, and it certainly won’t be the last.

Too many bees?

Before discussing urban bees and forage in more detail I’ll digress a minute to mention the suggestions that the inexorable rise and rise of urban beekeeping is threatening our native pollinators.

Actually … more than suggestions.

There are a number of scientific reports and reviews that indicate that urban beekeeping harms – by outcompeting – native pollinators like solitary bees. A recent report by the Royal Botanic Gardens at Kew states:

‘Campaigns encouraging people to save bees have resulted in an unsustainable proliferation in urban beekeeping. This approach only saves one species of bee, the honeybee, with no regard for how honeybees interact with other, native species.’

‘In some places, such as London, so many people have established urban hives that the honeybee populations are threatening other bee species.’

Our bees (Apis mellifera) are generalists. They are not particularly well adapted to any flower or nectar/pollen source.

They are equal opportunists.

Individually, there are many solitary bee species or non-hymenopteran pollinators, that are ‘better’ adapted. They pollinate more efficiently, or collect more nectar, faster.

But honey bees arrive in the environment mob handed.

Thousands of them.

Actually, tens or hundreds of thousands of them if there are several hives in an apiary. They are a formidable force and can easily outcompete other pollinators that are either solitary or only live in small colonies.

Save the bees, save humanity

When you see the phrase “Save the bees” what it usually means is save the honey bees.

Save the bees ...

Save the bees …

What it should be encouraging is “Save anything but the honey bees, because they don’t need saving … actually, there are possibly too many of them altogether”.

But that’s a lot less catchy … and it won’t let the supermarket, or food manufacturer or whatever, illustrate their campaign with cute photos of pollen-laden honey bees returning to quaint white-painted WBC hives in some sort of idyllic rural scene 4.

I suppose a photo of a honey bee would be better than drawing of a wasp though … which is what the NRDC used for a (mis)information campaign on CCD (colony collapse disorder) a few years ago.

D’oh!

Anyway … saving the bees is usually “greenwash” or bee-washing as it was termed by MacIvor and Packer in a 2015 paper on bee hotels 5

I’ll return to this topic, and urban beekeeping, later in the winter 6.

The Town mouse bees and the Country mouse bees

Where was I?

Oh yes, my – as will shortly be clear – incorrect assumption that country bees have access to more diverse and richer sources of forage than their poor relatives living in the town.

There are many sorts of countryside and many sorts of urban environments.

A hive in an intensively farmed arable landscape could be located in hundreds of acres of wheat fields, where all of the hedgerows were grubbed up years ago and replaced – if they weren’t just removed altogether – with barbed wire 7

How different is that environment to the ‘concrete jungle’ of a modern city? 

Tokyo

Surely that must be a terrible environment for bees?

In contrast, the suburban sprawl that surrounds most cities is possibly a good place for bees to live. Lots of neat little gardens, each 8 with a profusion of flowering plants, each chosen to provide vibrant colour for a much longer period than native plants.

And I’m sure we can all think of forage-rich rural environments. Here the bees gorge on early crocus, then gorse, willow, oil seed rape, clover, lime, blackberry, fireweed and himalayan balsam, before finishing the season will full crops and corbiculae from the ivy.

Now, in a recent publication 9 scientists have compared the forage available to town and country bees, and the results are quite surprising.

Let the bees tell you

If you live in a country with enlightened right to roam laws (like Scotland) you could wander around the countryside recording all the forage available to bees.

But the laws in England are much less enlightened. However, your right to roam in either country does not extend to the land around a private house or building. 

So, although you might be able to determine the forage available in the Scottish countryside, you can’t be certain you would have good enough access to do the same in England. And in a city you could only map what forage was available by peering over fences from public roads. 

So Elli Leadbetter and colleagues let the bees do the work.

They established 20 observation hives. Ten were in the the centre of London and 10 in agricultural land to the North East and South West of London. The hives were 5 km from each other to avoid overlapping areas of forage. They used observation hives so that they could watch and record the waggle dances of foragers in the hives.

I’ve discussed the waggle dance before. It is used to communicate three important pieces of information about a forage source:

  • direction
  • distance
  • quality

The first two bits of information are encoded in the angle of the waggle run to the perpendicular and the duration of the waggle run. The quality is conveyed by the number of circuits a dancing working performs. It’s a case of ‘the more, the better’ … energetically higher quality resources 10 result in more circuits.

Having recorded thousands of these waggle dances, they used the direction and distance information to ‘map’ where the bees were foraging.

GIS data, land use and foraging bees

For many locations there exists a wealth of land use data (GIS data; Geographic Information Systems). Much of this is at high resolution. For each of the 20 observation hives they produced a map of land use within 2.5 km of the hive at a resolution of 25 m. 

Land use was defined in broad categories such as 11 buildings, woodland, arable, pasture, fruit, OSR (all in agricultural areas) and dense or sparse residential, parks, amenity grassland or railways (all in urban landscapes). 

They then used some clever mathematics to decode the waggle dances 12 to work out where the bees had been, converting the distance and direction components to geographic locations.

Urban (top) and rural foraging heat maps, overlaid on GIS land use maps (5 km diameter)

These locations were overlaid on the land use maps to produce ‘heat maps’ showing where the bees were foraging. The image above shows these heat maps. In the spring the urban bees (top left) were foraging intensively to the east and west of the hive and the rural bees (bottom left) were mainly foraging in two large areas to the south east and south west of the hive.

Foraging distance and nectar quality

Even a cursory look at the image above shows that the urban bees tended to forage closer to the hive than the rural bees. But remember, that’s just three snapshots during the season.

Waggle run duration – rural bees fly further

However, more detailed analysis confirmed that this was the case. Throughout the season, the bees in the agricultural landscape foraged further from the hive. I’m showing the log-transformed median waggle run duration (above) as this allows slightly easier comparison across the season. The further the wiggly ‘best fit’ line is above the horizontal axis, the longer the duration of the waggle dance run, and so the further the bees are flying to find the forage.

Interestingly, the median foraging distances were relatively short when compared with the maximum foraging distances from the decoded waggle dances. This applied wherever the bees lived. For urban bees the median was 492 m (max 9375 m) and for agricultural bees it was 743 m (max 8158 m 13 ).

Perhaps the agricultural bees were flying further because there was better quality nectar available at more distant sites?

Nectar concentration (% w/w) sampled from returning workers

They controlled for this by recovering returning foragers and robbing them of their nectar load before analysing the sugar content. There was no significant difference 14 between the nectar from agricultural or urban landscapes. The sugar content of the nectar was recorded as reducing through the season.

Foraging preferences

So where did the town bees and the country bees prefer to forage?

City rooftop bees

City rooftop bees …

In urban areas the bees exhibited a strong preference for residential gardens (the ‘sparse residential land’) … these are presumably the flower-rich urban gardens that the homeowners also tend to prefer.

In contrast, bees in an agricultural landscape showed an entirely unsurprising reliance upon mass-flowering crops like oil seed rape (in spring only). They also showed weaker preferences for arable land and fruit crops throughout the season.

Mid-April in the apiary ...

Mid-April in a Warwickshire apiary …

I’ve skipped over a host of additional observations from the study, and almost all of the controls. Two things that are worth mentioning though.

Firstly, hive strength had no influence on waggle dance duration (and hence foraging distance). It therefore wasn’t the case that stronger hives had a larger workforce that could survey and exploit more distant forage. 

Secondly, cities are warmer due to the urban heat island effect. However, temperature also did not affect waggle dance duration when it was factored in. So, the city bees aren’t foraging at shorter distances because the dance is truncated at higher temperatures.

Conclusions

So, although cities are predominantly filled with buildings and roads, city bees travel less far to forage when compared to bees in agricultural landscapes.

This strongly suggests that the urban landscape consistently provided more available forage 15

Conversely, the bees in agricultural landscapes had to fly further, not because there were better quality nectar sources available at long-range, but because there wasn’t enough nectar nearby.

There were a number of additional interesting points in the paper, some of which were known already from other studies. For example, the high sugar content in spring nectar was already known (and confirmed here). Similarly, foraging distances in midsummer were longer than those in spring or autumn. This could be predicted due to the reduced rainfall in summer, and consequently the reduced overall level of nectar available.

I need to think more about how this study contributes – if at all – to the ‘too many bees in cities’ argument. If anything, forage-rich towns should be able to support a greater number of bees 16 without the honey bees impacting on other species. In contrast, honey bees in agricultural landscapes might dominate the available nectar sources because they can forage at long distances and then communicate to their nestmates the location.

Perhaps it just shows that that heavily farmed land is actually very poor in terms of nectar availability? It’s either boom or bust … once the OSR has finished, or the clover has been ploughed in, or the fruit trees stop flowering then there’s nothing left 🙁

It would be interesting to conduct a similar study in a forage-rich, non-agricultural, rural landscape.

Access all areas

Finally, I think a particularly neat thing about this study is the use of bees to ‘map’ the forage availability using what the authors term “a large-scale search effort that has no access limitations”. The scientists interpreted the waggle dance to get information that would otherwise have been difficult or impossible to determine.

However, using the bee’s own perception of the distances flown might actually lead to inaccuracies in the calculations. As discussed previously, bees measure distance by optic flow. Optic flow increases in complex landscapes … and cities are likely (at least to us, and certainly when compared with arable farmland, to bees) to be complex landscapes. Increased optic flow leads to a perception of increased distance, and hence to longer waggle runs.

This means that bees in complex landscapes might overestimate the distance they have actually flown to forage. Conversely, those in uniform landscapes might underestimate.

Which means that the results of this study may be a conservative estimate of the differences in foraging distance.

And therefore a conservative estimate of the differences in forage availability in urban and agricultural landscapes.


Notes

Dancing in the City was a pretty cheesy song that reached #3 in the charts for the rock-pop duo Marshall Hain in 1978. Having remembered the track when thinking up a title for this post, I made the mistake of listening to it on Spotify.

I now can’t get the damned thing out of my head. 

But it gets worse. I rummaged through Wikipedia and discovered that Kit Hain, the vocalist, subsequently had a very successful songwriting career with people like Roger Daltrey, Chaka Khan and Fleetwood Mac. Impressive. 

In contrast, Julian Marshall, the keyboard player became a member of the Flying Lizards who had a minor hit with a cover version of Barrett Strong’s 17 Money (That’s What I Want)

… and now I can’t get that out of my head 🙁

Fainting goats … and queens

Myotonia congenita is a genetic disorder that affects the muscles used for movement. Myotonia refers to the delayed relaxation of these skeletal muscles, resulting in a variety of obvious symptoms including temporary paralysis, stiffness or transient weakness.

In humans these symptoms are often manifest as difficulty in swallowing, gagging and frequent falls. Children are affected more than adults. One of the most dramatic manifestations are the falls (‘fainting’) that can occur as a result of a hasty movement. 

Although physiologically distinct, ‘fainting’ is a reasonably accurate description of the sudden loss of movement and the transient nature of the disorder. Like fainting, loss of movement is usually quickly resolved. However, unlike fainting, myotonia congenita involves muscular rigidity or stiffness, so more closely resembles catalepsy.

Genes

There are two types of myotonia congenita, termed Thomsen disease and Becker disease, both of which are usually associated with mutations in the gene CLCN1 1. This encodes a chloride channel (a ‘hole’ through the cell membrane that allows the transfer of chloride ions) critical for muscle fibre activity. 

Cartoon of a transmembrane chloride channel.

With loss-of-function mutations in CLNC1 the muscle fibre continues to to be activated. When stimulated, for example if the fibre is triggered to suddenly contract for jumping or running (or  to stop a fall), the muscle fibre is hyper-excitable and continues to contract, and shows delayed relaxation

Around 1 in 100,000 people exhibit myotonia congenita, though it is about ten times more common in northern Scandinavia. Treatment involves use of a number of anticonvulsant drugs.

The same loss-of-function CLCN1 mutation in humans is seen in symptomatically similar horses, dogs … and goats.

Goats

In the late 19th century four goats were imported to Marshall County, Tennessee. Their strange behaviour when startled was first described in 1904 and defined as a congenital myotonia by Brown and Harvey in 1939. 

The eponymous Tennessee fainting goat

These pre-war studies formed the basis of of our understanding of both the physiology and genetics of myotonia congenita, though the specific mutation in the CLCN1 gene was only confirmed several years after it had been identified in humans.

Since then myotonic goats have become an internet staple, with any number of slightly distressing (for me at least, if not for the goats) YouTube videos showing their characteristic fainting when surprised or frightened 2.

Don’t bother watching them.

If you want to see a fainting goat in action watch little ‘Ricky’ jump up onto a swinging seat on the National Geographic website.

It’s a perfect example.

He jumps up, gets a mild fright as the swing moves, goes stiff legged and simply rolls over and falls to the ground. A few moments later he’s back on his feet again, looking slightly shaken perhaps, but none the worse for wear.

Queens

All of that preamble was to introduce the topic of fainting queens. 

A fainting queen

This was a subject I’d heard about, but had no experience of until last week.

Periodically it gets discussed on Beesource or the Beekeepingforum – usually the topic is raised by a relatively small-time amateur beekeeper (like me) and it gets a little airtime before someone like Michael Palmer, Michael Bush, Hivemaker or Into the Lion’s Den 3 shuts down the conversation with a polite “Yes, I see it a few times a year. They recover”, or words to that effect.

Since these commercial guys handle hundreds or perhaps thousands of queens a year I think we can safely assume it’s a relatively rare phenomenon. 

Since I don’t handle hundreds or thousands of queens a year – and you probably don’t either – I thought the incident was worth recounting, so you know what to expect should it ever happen.

And to do that I have to first explain the fun I had with the first of the two queens in the hive I was inspecting.

A two queen colony

It was late afternoon and I was inspecting the last of our research colonies in the bee shed.

The hive had two brood boxes and a couple of supers. Nothing particularly surprising in that setup at this time of the season; the colony was quite strong, the spring honey had been extracted and a couple of supers had been returned to the hive for cleaning.

However, it wasn’t quite that straightforward. 

The lower brood box had been requeened ~3 weeks earlier with a mature queen cell from one of my queen rearing attempts. I’d seen that the virgin had emerged and restricted her to the lower box at my last visit. 

I’d added a queen excluder (QE) over the lower box with the intention of removing all the old frames above the QE once the brood had emerged.

However, at that last visit I’d ended up with a good looking 4 ‘spare’ virgin queen. Although I had no need for her at the time, and no time to make up a nuc 5, I decided to put her in a fondant-plugged introduction cage in this upper box.

This ‘upper’ queen couldn’t fly and mate in the week I was away, but I reasoned that I could merge the colony with the bottom box if the ‘lower’ queen failed to mate 6.

So, after adding the virgin queen to the top box I added a second QE and the two supers.

She can fly …

Having removed the supers and the upper QE I carefully inspected the upper box looking for the virgin queen who had been released from the cage

No sign of her 🙁

I went through the box again.

Time to try some of the ‘queen finding tricks’.

I moved three frames out of the way having examined them very carefully. The remaining 8 frames were then spaced out as four, well separated, pairs. I let the colony settle for a few minutes and then looked at the inner face of each pair of frames.

No sign of her 🙁

I looked again … nada, rien, niets, nunda, dim byd and sod it 7.

The obvious conclusion was that the colony had killed the queen after releasing her from cage. 

How uncharitable.

I reassembled the upper brood box and lifted it off the lower QE, in preparation to leave it outside the shed door while I went through the lower box. 

As I carried the brood box to the door I briefly looked up and saw a 8 virgin queen climbing up the inner pane of one of the shed windows, flapping frantically and fast approaching the opening that would allow her escape.

For obvious reasons I have no photographs of the next few minutes.

Bee shed window ...

Bee shed window …

For those unfamiliar with the bee shed windows, these have overlapping outer and inner panes, so are always open. They provide a very effective ‘no moving parts’ solution to clearing the shed of bees very quickly.

Which was the very last thing I wanted at that moment 😉

… rather well

I had a brood box and hive tool in my hands, the shed door was wide open, there was all sorts of stuff littering the floor and the virgin queen was inches away from making a clean getaway.

It’s worth noting that when virgin queens are disturbed and fly they almost always return to the hive. However, the hives in the shed have a single entrance and all the hives were already occupied with queens. I couldn’t let her fly and hope for the best … it probably wouldn’t end well.

By balancing half the brood box on an unoccupied corner of an adjacent hive roof I made a largely ineffective swipe for the queen, but disturbed her enough she flew away from the window in spirals around my head.

I    s  t  r  e  t  c  h  e  d    to reach the shed door and pulled it close, so reducing the possible exits from eight to seven. A small victory.

I put the brood box safely on the floor, leaning at an angle against the hive stand 9, and abandoned the hive tool.

The next 5 minutes were spent ineptly trying to catch the queen. When she wasn’t flying around the shed (where the lighting isn’t the best) she usually made for the same window.

The one behind the hive with four supers stacked on top 🙁

After a few more laps of the shed, dancing around the precariously balanced brood box and reaching around the hive tower for the window, I finally caught her.

And caged her 10.

I’m looking for publisher for my latest book, ‘Slapstick beekeeping’. If any readers know of a publisher please ask them to contact me.

After all that I should have had a little rest. I’d had enough excitement for the afternoon 11.

But there was still the queen in the bottom box to find and mark.

Feeling faint

The queen in the bottom box was mated and laying well. 

I made a near-textbook example of finding her 12.

After moving aside a few frames I should have announced (to the non-existent audience), She’s on the other side of the next frame … ” (the big reveal) ” … ah ha! There you are my beauty!”.

Holding the frame in one hand I checked my pockets for my marking cage 13.

All present and correct.

I then calmly picked her up by her wings. She was walking towards me, bending slightly as she crossed over another bee, so her wings were pushed up and away from her abdomen.

A perfect ‘handle’.

I didn’t touch her abdomen, thorax or head.

A swooning queen

And, as soon as I lifted her from the frame, she fell into a swoon and ‘dropped dead’.

This is an ex-parrot

Her wings were extended to the sides, her abdomen was curled round in a foetal position and she appeared completely motionless.

It is pining for the fjords

I dropped her into the marking cage and took the photo further up the page.

It was 6:49 pm.

For several minutes there was no obvious movement at all. Her legs and antennae were immobile. She showed no sign of breathing.

I gently shook her out onto a small piece of Correx on a nuc roof to watch and photograph her. I picked her up by the wing and held her in my palm … perhaps she needed some warmth to ‘come round’.

Was that a twitch?

Or was that me shaking slightly because I’d inadvertently killed her? 

Several more minutes of complete catatonia 14 passed … and then a gentle abdominal pulsing started.

This was now 10-11 minutes after I’d first picked her up.

Which got a bit stronger and was accompanied by a feeble waggle of the antennae.

And was followed a minute or so later by a bit of uncoordinated leg flexing.

And after 15 minutes she took her first steps.

It looked like she’d been on an ‘all nighter’ and was still rather the worse for wear.

I slipped her into a JzBz queen cage, sealed it with a plastic cap, and left it hanging between a couple of brood frames.

From picking her up to placing the caged queen into the brood box had taken 24 minutes.

Caged queen after fainting (and recovering … more or less)

I reasoned that if …

  • she fully recovered they’d feed her through the cage and I could release her the following morning
  • I’d released her immediately and she’d acted abnormally the colony might have killed her off
  • she did not recover I would at least be able to find the corpse easily ( 🙁  ) and so could confidently requeen the colony (with the virgin I’d tucked away safely in my pocket)

The following morning the cage was covered in bees and she looked just fine, so I released her. 

Somewhere under that lot is the recovered queen – still caged

She walked straight down between the frames as though nothing untoward had happened.

I didn’t have the heart to mark and clip her … I didn’t want to risk her ‘fainting’ again and, if she had, didn’t have the time to hang around while she recovered 15.

So was this ‘fainting’ myotonia congenita?

I suspect not.

Another name for the Tennessee fainting goat is the ‘stiff-legged’ goat. This reflects the characteristic rigidity in the limbs when the muscles fail to relax. The queen’s legs were curled under her, rather than being splayed out rigidly.

However, this interpretation may simply reflect my near complete ignorance of the musculature of honey bees 😉

However, I do know that the basics of muscle contraction and relaxation are essentially the same in invertebrate and vertebrate skeletal muscle. There are differences in the innervation of muscle fibres, but the fundamental role of chloride channels in allowing muscle relaxation is similar.

Therefore, for this fainting queen to be affected by myotonia congenita she should have a mutation in the CLCN1 gene encoding the chloride channel.

Although the honey bee genome has been sequenced a direct homolog for CLCN1 appears not to have been identified, though there are plenty of other chloride channels present 16

The majority of the 60 or so mapped mutations associated with myotonia congenita (in humans) are recessive. Two copies of the mutated gene (in diploids, like humans or female honey bees) are needed for the phenotype to occur.

Of course, drones are haploid so it should be easier to detect the phenotype.

I’ve never heard of drones ‘fainting’ when beekeepers practise their queen marking skills on them. Have you?

Repeated fainting

I’ll try to mark and clip this queen again.

It will be interesting to see if she behaves in the same way 17.

A quick scour of the literature (or what passes for the ‘literature’ on weird beekeeping phenomena i.e. the discussion fora) failed to turn up examples of the same queen repeatedly fainting.

Or any mention of daughter queens showing the same behaviour.

All of which circumstantially argues against this being myotonia congenita.

However, there are many other causes of sudden fainting (from the NHS website):

  • standing up too quickly – (low blood pressure)
  • not eating or drinking enough
  • being too hot
  • being very upset, angry, or in severe pain
  • heart problems
  • taking drugs or drinking too much alcohol

… though I can exclude the last one as my bees are teetotal 😉

So, there you have it, a brief account of a cataleptic queen … and her recovery.


Notes

A fortnight after the events described above I clipped and marked the queen. I did everything the same – picked her up by the wings in the shed (so again not exposed to bright sunlight – which may be relevant, see the comment by Ann Chilcott).

She (the queen) didn’t faint. She behaved just like the remaining 4 queens I marked on the same afternoon.

So no repeat of the ‘amateur dramatics’ 🙂

It’s a drone’s life

What has a mother but no father, but has both a grandmother and grandfather?

If you’ve not seen this question before you’ve not attended a ‘mead and mince pies’ Christmas quiz at a beekeeping association. 

Drone

Drone … what big eyes you have …

The answer of course is a drone. The male honey bee. Drones are produced from unfertilised eggs laid by the queen, so formally they have no father. Drones are usually haploid (one set of chromosomes), whereas queens and workers are diploid 1

Anyway, enough quiz questions. With the relaxation in Covid restrictions we may all be able to attend in person this Christmas 2, so I don’t want to spoil it by giving all the answers away in advance.

The long cold spring has been pretty tough for new beekeepers, it’s been a struggle for smaller colonies and it’s been really hard for drones.

Spring struggles

New beekeepers have had to develop the patience of Job to either acquire bees in the first place or start their inspections. Inevitably new beekeepers are bursting with enthusiasm 3 and the cold northerlies, unseasonal snow (!) and low temperatures have prevented inspections and delayed colony development (and hence the availability and sale of nucs).

Small colonies 4 are struggling to rear brood and to collect sufficient nectar and pollen.

This is an interesting topic in its own right and deserves a post of its own 5. In a nutshell, below a certain threshold of bees, colonies are unable to keep the brood warm enough and have sufficient foragers to collect nectar and pollen.

As a consequence, smaller colonies are low on stores and at risk of starvation. 

It’s a Catch-22 situation … to rear sufficient brood to collect an excess of nectar (or pollen) the colony needs more adult workers. 

I don’t know what the cutoff is in terms of adult bees, but most of my colonies with <7 frames of brood have needed feeding this spring.

One feature of these smaller colonies is that, unless they have entire frames of drone comb 6, there is little if any drone brood in the hive.

There might be drones present in the colony, but I don’t know whether they were reared there or drifted there from another hive.

And, for those of us attempting to rear queens, drones are an essential indicator that queen mating will be timely and successful.

On a brighter note …

But it’s not all gloom and doom.

Strong colonies are doing very well.

Several of mine have a box packed full of brood and I’m relying on a combination of …

  • lots of space by giving them more supers than they need
  • low ambient temperatures
  • crossed fingers

… as my swarm prevention strategy 😉

Beginners take note … one of these is likely to help (space), one is frankly pretty risky (chilly) and the last is not a proven method despite being widely used by many beekeepers 😉

I’m pretty confident that colonies will not swarm at 13-14°C.

I am inspecting colonies every 7 days and have only seen two with charged queen cells. One was making early swarm preparations; I used the nucleus method of swarm control and then split the colony into nucs a fortnight ago 7.

The other colony contained my first attempt at grafting this year, which seems to have gone reasonably well 8.

Lots of brood, nectar and drones

A typical brood frame from one of these strong colonies contains a good slab of sealed or open brood, some pollen around the sides and an interrupted arc of fresh nectar above the brood. 

In the photo above you can see pollen on the right hand side of the frame and glistening fresh nectar in the top left and right hand corners.

Typically these strong colonies also have partially filled supers, though it’s pretty clear that the oil seed rape is likely to go over before the weather warms enough (or the colonies get strong enough) to fully exploit it.

Spring honey is going to be in short supply and my fantastic new honey creamer is going to sit idle 🙁

Drones

What you probably can’t really see in the picture above is that these strong colonies also contain good numbers of drones.

Strong colonies … ample drones

I can count about a dozen in the closeup above. 

I like seeing drones in a strong, healthy colony early(ish) in the season 9.

Firstly, the presence of drones indicates that the colony (and presumably others in the neighbourhood which are experiencing a similar environment and climate) will soon be making swarm preparations. This means I need to redouble my efforts to check for queen cells to avoid losing swarms 🙁  … think of it as a long-range early warning system.

But it also means I can start thinking about queen rearing 🙂

Secondly, although these drones are unlikely to mate with my queens, you can be sure they’re going to have a damned good go at mating with queens from other local apiaries.

In addition to being strong and healthy, this colony is well-tempered, steady on the comb and pleasant to work with. The production of a few hundred thousand frisky drones prepared to lay down their lives 10 to improve the local gene pool is my small act of generosity to local beekeepers 11.

How many drones?

Honey bee colonies that nest in trees or other natural cavities produce lots of drone comb. Studies of feral colonies on natural comb show that about 17% of the comb is dedicated to rearing drones (but also used for storing nectar at other times of the season).

Foundationless triptych ...

Foundationless triptych …

Similarly, beekeepers who predominantly use foundationless frames regularly see significantly greater amounts of drone comb (and drone brood and drones) in their colonies. With the three-panel bamboo-supported frames I use it’s not unusual for one third of some frames to be entirely drone comb.

In contrast, beekeepers who only use standard worker foundation will be used to seeing drone comb occupying much less of the brood nest. Under these circumstances it’s usually restricted to the edges or corners of frames.

However, given the opportunity e.g. a damaged patch of worker comb or if you add a super frame into the brood box, the workers will often rework the comb (or build new brace comb) containing just drone cells.

The bees only build drone comb when they need it.

A newly hived swarm will build sheet after sheet of new comb, but it will all be for rearing worker brood. If you give them foundationless frames they only build worker comb and if you provide worker foundation they don’t rework it to squeeze in a few drone cells.

The colony will also not build new drone comb late in the season. Drone comb is drawn early in the season because the drones are needed before queens are produced.

The timing of drone production

Studies in the late 1970’s 12 demonstrated that drone brood production peaks about one month before the the main period of swarming. Similar studies in other areas have produced similar results.

Why produce all those drones when there are no queens about?

The timing is due to the differences in the development time (from egg to eclosion) of drones and queens, together with the differences in the time it takes before they are sexually mature.

Drones take 50% longer to develop than queens – 24 days vs. 16 days. After emergence the queen take a few days (usually quoted as 5-6) to reach sexual maturity before she embarks on her mating flight(s).

In contrast, drones take from 6-16 days to reach sexual maturity.

Swarming tends to occur when charged queen cells in the hive are capped. These cells will produce new virgin queens about a week later and – weather permitting – these should go on mating flights after a further six days. 

Therefore a colony that swarms in very early June will need sexually mature drones available 12-14 days later (say, mid-June) to mate with the newly emerged queen that will subsequently return to head the swarmed colony. These drones will have to have hatched from eggs laid in the first fortnight of May to ensure that they are sexually mature at the right time.

Decisions, decisions

How does the colony know to produce drones at the right time? Is it the workers or the queen who makes this decision?

I’ve recently answered a question on this topic for the Q&A pages in the BBKA Newsletter. In doing some follow-up reading I’ve discovered that (inevitably) it’s slightly more complicated than I thought … which was already pretty complicated 🙁

The workers build the comb and therefore determine the amount of drone vs. worker comb the brood nest contains.

I don’t think it’s known how the workers measure the amount of brood comb in the nest, but they clearly can. We do know that bees can count 13 and that they have some basic mathematical skills like addition and subtraction.

Perhaps these maths skills 14 include some sort of averaging, allowing them to sample empty cells, measure them and so work out the proportion that are drone or worker.

Whatever form this ‘counting’ takes, it requires direct contact of the bees with the comb. You cannot put a few frames of drone comb in the hive behind a mesh screen and stop the bees from building more drone comb. It’s not a volatile signal that permeates the hive.

However they achieve this, they are also influenced by the amount of capped drone brood already present in the colony. If there’s lots already then the building of additional drone comb is inhibited 15.

Colonies therefore regulate drone production through a negative feedback process.

So … does the queen simply lay every cell she comes across, trusting the worker population has provided the correct proportions of drone and worker comb?

Not quite

Studies by Katie Wharton and colleagues 16 showed that the queen could also regulate drone production.

Wharton confined queens on 100% drone or worker comb in a frame-sized queen ‘cage’ for a few days.

Frame sized queen ‘cage’ …

She then replaced the comb in the cage with 50:50 mix of drone and worker comb and recorded the number of eggs laid in drone or worker cells over a 24 hour period (and then allowed the eggs to develop).

Queens that had only been able to lay worker brood for the first four days of confinement laid significantly more drone brood when given the opportunity.

The scientists showed reasonably convincingly that this was a ‘decision’ made by the queen, rather than influenced by the workers e.g. by preparing biased number of drone or worker cells for eggs to be laid in, by preferentially ‘blocking’ certain cell types with honey or by selectively cannibalising drone or worker eggs.

Interestingly, queens initially confined on worker comb laid significantly (~25%) more eggs on the 50:50 comb than those confined on drone comb. I’m not sure why this is 17.

Wharton and colleagues conclude “these results suggest that the regulation of drone brood production at the colony level may emerge at least in part by a negative feedback process of drone egg production by the queen”.  

So it seems likely that drone production in a colony reflects active decisions made by both workers and the queen.

Why has this spring been really hard for drones?

To be ready for swarming, colonies therefore need to start drone production quite early in the season – at least 4-5 weeks before any swarms are likely.

Late May ’21 forecast. Swarmy weather? I don’t think so …

But with consistently poor weather, these drones are unlikely to be needed. Colonies will not have built up enough to be strong enough to swarm.

Producing drones is a high energy process – they are big bees and require a lot of carbohydrate and protein during development.

Under natural conditions 18 a colony puts as many resources into drone production over the season as it does into swarms.

Thomas Seeley has a nice explanation of this in The Lives of Bees – if you take the dry weight of primary swarms and casts produced by a colony it’s about the same as the dry weight of drones produced throughout the season. 

Rather than waste energy in drone production the workers remove unwanted drone eggs and larvae. The queen lays them, but the workers prevent them being reared.

How do the workers decide the drones aren’t going to be needed?

Do workers have excellent long-range weather forecasting abilities?

Probably not 19

If the weather is poor the colony will be unable to build up properly because forage will be limited. As a consequence, the colony (and others in the area) would be unlikely to swarm and so drones would not be needed for queen mating.

Free and Williams (1975) demonstrated that forage availability was the factor that determined whether drones were reared and maintained in the colony. 

Under conditions where forage was limited, drone eggs and larvae were rejected (cannibalised) and adult drones were ejected from the hive.

Unwanted drone ejected from a colony in early May

Beekeepers are familiar with drones being ejected from colonies in the autumn (again, a time when forage becomes limiting), but it also happens in Spring.

And at other times when nectar is in short supply …

Those of you currently enjoying a good nectar flow from the OSR should also look at colonies during the ‘June gap’. With a precipitous drop in nectar available in the environment once the OSR stops yielding, colonies can be forced to eject drones.

It’s tough being a drone … which may explain why one of my PhD students has the name @doomeddrone on Twitter 😉


 

Acting on Impulse

Men just can’t help acting on Impulse … 

This was the advertising strapline that accompanied the 1982 introduction of a new ‘body mist’ perfume by Fabergé. It was accompanied by a rather cheesy 1 set of TV commercials with surprised looking (presumably fragrant) women being accosted by strange men proffering bouquets of flowers 2.

Men just can’t help acting on Impulse …

And, it turns out that women – or, more specifically, female worker honey bees – also act on impulse

In this case, these are the ‘impulses’ that result in the production of queen cells in the colony.

Understanding these impulses, and how they can be exploited for queen rearing or colony expansion (or, conversely, colony control), is a very important component of beekeeping.

The definition of the word impulse is an ‘incitement or stimulus to action’.

The action, as far as our bees are concerned, is the development of queen cells in the colony.

If we understand what factors stimulate the production of queen cells we can either mitigate those factors – so reducing the impulse and delaying queen cell production (and if you’re thinking ‘swarm prevention‘ here you’re on the right lines) – or exploit them to induce the production of queen cells for requeening or making increase.

But first, what are the impulses?

There are three impulses that result in the production of queen cells – supersedure, swarm and emergency.

Under natural conditions i.e. without pesky meddling by beekeepers, colonies usually produce queen cells under the supersedure or swarm impulse.

The three impulses are:

  1. supersedure – in which the colony rears a new queen to eventually replace the current queen in situ
  2. swarm – during colony reproduction (swarming) a number of queen cells are produced. In due course the current queen leaves heading a prime swarm. Eventually a newly emerged virgin queen remains to get mated and head the original colony. In between these events a number of swarms may also leave headed by virgin queens (so-called afterswarms or casts).
  3. emergency – if the queen is lost or damaged and the colony rendered queenless, the colony rears new queens under the emergency impulse.

Many beekeepers, and several books, state that you can determine the type of impulse that induced queen cell production by the number, appearance and location of the queen cells.

And, if you can do this, you’ll know what to do with the colony simply by judging the queen cells.

If only it were that simple

Wouldn’t it be easy?

One or two queen cells in the middle of frame in the centre of the brood nest? Definitely supersedure. Leave the colony alone and the old queen will be gently replaced over the next few weeks. Brood production will continue uninterrupted and the colony will stay together and remain productive.

A dozen or more sealed queen cells along the bottom edge of a frame? The colony is definitely  in swarm mode and – since the cells are already capped – has actually already swarmed. Time to thin out the cells and leave just one to ensure no casts are also lost.

But it isn’t that simple 🙁

Bees haven’t read the textbooks so don’t necessarily behave as expected.

I’ve found single open queen cells in the middle of a central frame, assumed it was supersedure, left the colony alone and lost a swarm from the hive a few days later 🙁

D’oh!

Or I’ve found loads of capped queen cells on the edges of multiple frames in a hive, assumed that I’d missed a swarm … only to subsequently find the original marked queen calmly laying eggs as I split the brood box up to make several nucleus colonies  🙂

Not all queen cells are ‘born’ equal

It’s worth considering what queen cells are … and what they are not. And how queen cells are started.

There are essentially two ways in which queen cells are started.

They are either built from the outset as vertically oriented cells into which the queen lays an egg, or they start their life as horizontally oriented 3 worker cells which, should the need arise, are re-engineered to face vertically.

Play cup or queen cell?

Play cup or are they planning their escape …?

Queen cells started under the supersedure or swarming impulse are initially created as ‘play cups‘. A play cup looks like a small wax version of an acorn cup – the woody cup-like structure that holds the acorn nut. In the picture above the play cup is located on the lower edge of a brood frame, but they are also often found ‘centre stage‘ in the middle of the frame.

Play cups

A colony will often produce many play cups and their presence is nothing to be concerned about. In fact, I think it’s often a rather encouraging sign that the colony is sufficiently strong and healthy that it might be thinking of raising a new queen. 

Before we leave play cups and consider how emergency queen cells start life it’s worth emphasising the differences between play cups and queen cells.

Play cups are not the same as queen cells

Until a play cup is occupied by an egg it is not a queen cell.

At least it’s not as far as I’m concerned 😉

And, even if it contains an egg there’s no guarantee it will be supported by the workers to develop into a new queen 4.

However, once the cell contains a larva and it is being fed by the nurse bees – evidenced by the larva sitting in an increasingly thick bed of royal jelly – then it is indisputably a queen cell.

Charged queen cell ...

Charged queen cell …

And to emphasise the fundamental importance in terms of colony management I usually refer to this type of queen cell as a ‘charged queen cell’.

Once charged queen cells appear in the colony, all other things being equal, they will be maintained by the workers, capped and – on the 16th day after the egg was laid – will emerge as a new queen.

And it is once charged queen cells are found in the colony that swarm control should be considered 5.

But let’s complete our description of the queen cells by considering those that are produced in response to the emergency impulse.

Emergency queen cells

Queen cells produced under the emergency impulse differ from those made under the swarm or supersedure impulse. These are the cells that are produced when the colony is – for whatever reason – suddenly made queenless. 

Without hamfisted beekeeping it’s difficult to imagine or contrive a scenario under which this would occur naturally 6, but let’s not worry about that for the moment 7

The point is that, should a colony become queenless, the workers in the colony can select one or more young larvae already present in worker cells and rear them as new queens.

So, although the eggs are (obviously!) laid by the queen 8, they have been laid in a normal worker cell. To ensure that they get lavished with attention by the nurse bees, feeding them a diet enriched in Royal Jelly, the cell must be re-engineered to project vertically downwards.

Location, location

Queen cells can occur anywhere in the hive to which the queen has access.

Queen cell on excluder

Queen cell on underside of the excluder …

But they are most usually found on the periphery of the frame, either along the lower edge …

Queen cells ...

Queen cells …

… or a vertical side edge of the frame …

Sealed queen cells

… but they can also be found slap, bang in the middle of a brood frame.

Single queen cell in the centre of a frame

And remember that bees have a remarkable ability to hide queen cells in inaccessible nooks and crannies on the frame … and that finding any queen cells is much more difficult when the frame is covered with a wriggling mass of worker bees.

Location and impulses

Does the location tell us anything about the impulse under which the bees generated the queen cell?

Probably not, or at least not reliably enough that additional checks aren’t also needed 🙁

Many descriptions will state that a small number (typically 1-3) of queen cells occupying the centre of a frame are probably supersedure cells. 

Whilst this is undoubtedly sometimes or even often true, it is not invariably the case.

The workers choose which larvae to rear as queens under the emergency impulse. If the only larvae of a suitable age are situated mid-frame then those are the ones they will choose.

In addition, since generating emergency cells requires re-engineering worker cells, newer comb is likely more easily manipulated by the workers.

Some beekeepers ‘notch’ comb under suitably aged larvae to induce queen cell production at particular sites on the frame 9. The photograph shows a frame of eggs with a notch created with the hive tool. It’s better to place the notch underneath suitably aged larvae, not eggs. Clearly, the age of the larvae is more critical than the ease with which the comb can be reworked. Those who use this method [PDF] properly/extensively claim up to a 70% ‘success’ rate in inducing queen cell placement on the frame. This can be very useful if the plan is to cut the – well separated – queen cells out and use them in mating nucs or for requeening other colonies.

Eggs in new comb ...

Eggs in new comb …

Comb at the bottom or side edges of the frame often has space adjacent and underneath it. Therefore the bees might favour these over sites mid-frame (assuming ample suitable aged larvae) simply because the comb is easier to re-work in these locations.

And don’t forget … under the emergency impulse the colony preferentially chooses the rarest patrilines to rear as new queens 10.

Not all larvae are equal, at least when rearing queens under an emergency impulse.

Active queen rearing and the three impulses

By ‘active’ queen rearing I mean one of the hundreds of methods in which the beekeeper is actively involved in selecting the larvae from which a batch of new queens are reared.

This doesn’t necessarily mean grafting , towering cell builders and serried rows of Apidea mini nucs.

It could be as simple as taking a queen out of a good colony to create a small nuc and then letting the original colony generate a number of queen cells.

Almost all queen rearing methods use either the emergency or supersedure impulses to induce new queen cell production 11.

For example, let’s consider the situation described above.

Active queen rearing and the emergency impulse

A strong colony with desirable traits (calm, productive, prolific … choose any three 😉 ) is made queenless by removing the queen on a frame of emerging brood into a 5 frame nucleus hive. With a frame of stores and a little TLC 12 the queen will continue to lay and the nuc colony will expand.

Everynuc

Everynuc …

But the, now queenless, hive will – under the emergency impulse – generate a number of new queen cells. These will probably be distributed on several frames if the queen was laying well before she was removed.

The colony will select larvae less than ~36 hours old (i.e. less than 5 days since the egg was laid) for feeding up as new queens.

If the beekeeper returns to the hive 8-9 days later it can be split into several 5 frame nucs, each containing a suitable queen cell and sufficient emerging and adherent bees to maintain the newly created nucleus colony 13.

Active queen rearing and the supersedure impulse

In contrast, queenright queen rearing methods such as the Ben Harden system exploit the supersedure impulse.

Queen rearing using the Ben Harden system

In this method suitably aged larvae are offered to the colony above the queen excluder. With reduced levels of queen pheromones present – due to the physical distance and the fact that queen cannot leave a trail of her footprint pheromone across the combs above the QE – the larvae are consequently raised under the supersedure impulse.

Capped queen cells

Capped queen cells produced using the Ben Harden queenright queen rearing system

I’m always (pleasantly) surprised this works so well. Queen cells can be produced just a few inches away from a brood box containing a laying queen, with the workers able to move freely through the queen excluder. 

Combining impulses …

Finally, methods that use Cloake or Morris boards 14 use a combination of the emergency and supersedure impulses.

Cloake board ...

Cloake board …

In these methods the colony is rendered transiently queenless to start new queen cells. About 24 hours later the queenright status is restored so that cells are ‘finished’ under the supersedure response.

The odd one out, as it’s not really practical to use it for active queen rearing, is the swarming impulse. Presumably this is because the conditions used to induce swarming are inevitably rather difficult to control. Active queen rearing is all about control. You generally want to determine the source of the larvae used and the timing with which the queen cells become available.

Environmental conditions can also influence colonies on the brink of swarming … literally a case of rain stopping play.

Acting on impulse

If there are play cups in the colony then you don’t need to take any action 15, but if there are charged queen cells present then your bees are trying to tell you something.

Precisely what they’re trying to tell you depends upon the number and position of the queen cells, the state or appearance of those cells, and the state of the colony – whether queenright or not.

What you cannot do 16 is decide what action to take based solely on the number, appearance or position of the queen cells you find in the colony. 

Is the colony queenright?

Are there eggs present in the comb?

Does the colony appear depleted of bees?

If there are lots of sealed queen cells, no eggs, no sign of the queen and a depleted number of foragers then the colony has probably swarmed. 

Frankly, this is pretty obvious, though it’s surprising the number of beekeepers who cannot determine whether their colony has swarmed or not.

But other situations are less clear … 

If there are a small number of charged queen cells, eggs, a queen and a good number of bees in the hive then it might be supersedure.

Or the colony might swarm on the day the first cell is sealed 🙁

How do you distinguish between these two situations? 

Is it mid-May or mid-September? Swarming is more likely earlier in the season, whilst supersedure generally occurs later in the season.

But not always 😉

Is the queen ‘slimmed down’ and laying at a reduced rate?

Much trickier to determine … but if she is then they are likely to swarm.

Decisions, decisions 😉 … and going by the number of visits to my previous post entitled Queen cells … don’t panic! there are lots of beekeepers trying to make these decisions right now 🙂


 

Quick thinking & second thoughts

I gave my last talk of the winter season on Tuesday to a lovely group at Chalfont Beekeepers Society. The talk 1 was all about nest site selection and how we can exploit it when setting out bait hives to capture swarms.

It’s an enjoyable talk 2 as it includes a mix of science, DIY and practical beekeeping.

Nest sites, bait hives and evolution

The science would be familiar to anyone who has read Honeybee Democracy by Thomas Seeley. This describes his studies of the features considered important by the scout bees in their search for a new nest site 3.

Under offer ...

Under offer …

The most important of these are:

  • a 40 litre cavity (shape unimportant)
  • a small entrance of 10-15cm2
  • south facing
  • shaded but in full view
  • over 5m above ground level
  • smelling of bees

All of which can easily be replicated using a National brood box with a solid floor. Or two stacked supers.

And – before you ask – a spare nuc box is too small to be optimal.

That doesn’t mean it won’t work as a bait hive, just that it won’t work as well as one with a volume of 40 litres 4.

Evolution has shaped the nest site selection process of honey bees. They have evolved to preferentially occupy cavities of about 40 litres.

Presumably, colonies choosing to occupy a smaller space (or those that didn’t choose a larger space 5 ) were restricted in the amount of brood they could raise, the consequent strength of the colony and the weight of stores they could lay down for the winter.

Get these things wrong and it doesn’t end well 🙁

A swarm occupying a nuc box-sized cavity would either outgrow it before the end of the season, potentially triggering another round of swarming, or fail to store sufficient honey.

Or both.

Over thousands of colonies and thousands of years, swarms from colonies with genetics that chose smaller cavities would tend to do less well. In good years they might do OK, but in bad winters they would inevitably perish.

Bait hive compromises

If you set out a nuc box as a bait hive, you’re probably not intending to leave the swarm in that box.

But the bees don’t know that. Their choices have been crafted over millenia to give them the best chance of survival.

All other things being equal they are less likely to occupy a nuc box than a National brood box.

Another day, another bait hive, another swarm …

For this reason I don’t use nuc boxes as bait hives.

However, I don’t recapitulate all the features the scout bees look for in a ‘des res’.

I studiously ignore the fact that bees prefer to occupy nest sites that are more than 5 metres above ground level.

This is a pragmatic compromise I’m prepared to make for reasons of convenience, safety and enjoyment.

Bees have probably evolved to favour nest sites more than 5 metres above ground level to avoid attention from bears. The fact that there are no bears in Britain, and haven’t been since the Middle Ages 6, is irrelevant.

The preference for high altitude nest sites was ‘baked into’ the genetics of honey bees over the millenia before we hunted bears 7 to extinction.

However, I ignore it for the following reasons:

  • convenience – I usually move occupied bait hives within 48 hours of a swarm arriving. It’s easier to do this from a knee height hive stand than from a roof ladder.
  • safety – I often move the bait hive late in the evening. Rather than risk disturbing a virgin queen on her mating or orientation flights (assuming it’s a cast that has occupied the bait hive) I move them late in the day. In the ‘bad old days’ when I often didn’t return from the office until late, this was sometimes in the semi-dark. Easy and safe to do at knee height … appreciably less so at the top of a ladder.
  • enjoyment – I can see the scout bees going about their business at a hive near ground level without having to get the binoculars out. Their behaviour is fascinating. If you’ve not watched them I thoroughly recommend it.

Scout bee activity

The swarming of honey bees is a biphasic process. In the first phase the colony swarms and forms a temporary bivouac nearby to the original nest site.

The two stage process of swarming

The scout bees search an area ~25 km2 around the bivouacked swarm for suitable nest sites. They communicate the quality and location of new nest sites by performing a waggle dance on the surface of the bivouac.

Once sufficient scouts have been convinced of the suitability of one of the identified nest sites the second phase of swarming – the relocation of the swarm – takes place.

Swarm of bees

Swarm of bees

However, logic dictates that the scout bees are likely to have already identified several potential new nest sites, even before the colony swarms and clusters in a bivouac.

There are only a few hundred scout bees in the swarmed colony, perhaps 2-3% of the swarm.

Could just a few hundred scouts both survey the area and reach a quorum decision on the best location within a reasonable length of time?

What’s a reasonable length of time?

The bivouacked swarm contains a significant amount of honey stores (40% by weight) but does not forage. It’s also exposed to the elements. If finding sites and reaching a decision on the best nest site isn’t completed within a few days the swarm may perish.

Which is why I think that scout bees are active well before the colony actually swarms.

Early warning systems

If scout bees are active before a colony swarms they could be expected to find and scrutinize my bait hive(s).

If I see them doing this I’m forewarned that a colony within ~3 km (the radius over which scout bees operate) is potentially making swarm preparations.

Since I’ll always have a bait hive or two within 3 km of my own apiaries I’ll check these hives at the earliest opportunity, looking for recently started queen cells.

Whether they’re my colonies or not, it’s always worth knowing that swarming activity has started. Within a particular geographic area, with similar weather and forage, there’s usually a distinct swarming period.

If it’s not one of my colonies then it soon might be 😉

So, in addition to just having the enjoyment of watching the scout bees at work, a clearly visible – ground level – bait hive provides a useful early warning system that swarming activity has, or soon will, start.

Questions and answers

Although talking about swarms and bait hives is enjoyable, as I’ve written before, the part of the talk I enjoy the most is the question and answer session.

And Tuesday was no exception.

I explained previously that the Q&A sessions are enjoyable and helpful:

Enjoyable, because I’m directly answering a question that was presumably asked because someone wanted or needed to know the answer 8.

Helpful, because over time these will drive the evolution of the talk so that it better explains things for more of the audience.

Actually, there’s another reason in addition to these … it’s a challenge.

A caffeine-fueled Q&A Zoom session

It’s fun to be ‘put on the spot’ and have to come up with a reasonable answer.

Many questions are rather predictable.

That’s not a criticism. It simply reflects the normal range of topics that the audience either feels comfortable asking about, or are interested in. Sometimes even a seemingly ‘left field’ question, when re-phrased, is one for which there is a standard answer. The skill in this instance is deciphering the question and doing the re-phrasing.

But sometimes there are questions that make you think afresh about a topic, or they force you to think about something you’ve never considered before.

And there was one of those on Tuesday which involved biphasic swarming and scout bee activity.

Do all swarms bivouac?

That wasn’t the question, but it’s an abbreviated form of the question.

I think the original wording was something like:

Do all swarms cluster in a bivouac or do some go directly from the original hive/location to the new nest site?

And I didn’t know the answer.

I could have made a trite joke 9 about not observing this because my own colonies swarm so infrequently 🙄

I could have simply answered “I don’t know”.

Brutally honest, 100% accurate and unchallengeable 10.

But it’s an interesting question and it deserved better than that.

So, thinking about it, I gave the following answer.

I didn’t know, but thought it would be unlikely. For a swarm to relocate directly from the original nest site the scout bees would need to have already reached a quorum decision on the best location. To do this they would need to have found the new nest site (which wouldn’t be a problem) and then communicate it to other scout bees, so that they could – in turn – find the site. Since this communication involves the waggle dance it would, by definition, occur within the original hive. Lots of foragers will also be waggle dancing about good patches of pollen and nectar so I thought there would be confusion … perhaps they always need to form a bivouac on which the scout bees can dance? Which explains why I think it’s unlikely.

In a Zoom talk you can’t ponder too long before giving an answer or the audience will assume the internet has crashed and they’ll drift off to make tea 11.

An attentive beekeeping audience … I’d better think fast or look stupid

You therefore tend to mentally throw together a few relevant facts and assemble a reasonable answer quite quickly.

And then you spend the rest of the week thinking about it in more detail …

Second thoughts

I still don’t know the answer to the question Do all swarms bivouac?”, but I now realise my answer made some assumptions which might be wrong.

I’ll come to these in a minute, but first let me address the question again with the help of the people who actually did the work.

I’ve briefly looked back through the relevant literature by Seeley and Lindauer and cannot find any mention of swarms relocating without going via a bivouac. I may well have missed something, it wouldn’t be the first time 12.

However, their studies are a little self-selecting and may have overlooked swarms that behaved like this.

Both were primarily interested in the waggle dance and the decision making process, they therefore needed to be able to observe it … most easily this is on the surface of the bivouac.

Martin Lindauer mainly studied colonies that had naturally swarmed, naming them after the location of the bivouac, and then studied the waggle dancing on the surface of the clustered swarm. In contrast, Tom Seeley created swarms by caging the queen and adding thousands of very well fed bees.

Absence of evidence is not evidence of absence.

So, what were the assumptions I made?

There were two and they both relate to confusion between waggle dancing foragers and scout bees.

  1. Swarming usually occurs during a strong nectar flow. Therefore there are likely to be lots of waggle dancing foragers in the hive at the same time the scouts are trying to persuade each other – using their own fundamentally similar – waggle dances.
  2. Bees ‘watching’ are unable to distinguish between scouts bees and foragers.

So, what’s wrong with these assumptions?

A noisy, smelly dance floor

Foragers perform the waggle dance on the ‘dance floor’. This is an area of vertical comb near the hive entrance. It’s position is not fixed and can move – further into the hive if the weather is cold, or even out onto a landing board (outside the hive) in very hot weather 13.

So, although the dance floor occupied by foragers isn’t immovable, it is defined. There’s lots of other regions of the comb that scouts could use for their communication i.e. there could be spatial separation between the forager and scout bee waggle dances.

Secondly, foragers provide both directional and olfactory clues about the identity and location of good sources of pollen and nectar. In addition to two alkanes and two alkenes produced by dancing foragers 14 they also carry back scents “acquired from the environment at or en route to the floral food source” which are presumed to aid foragers recruited by the waggle dancer to pinpoint the food source.

Importantly, non-dancing returning foragers do not produce these alkanes and alkenes. Perhaps the dancing scouts don’t either?

A dancing scout would also lack specific scents from a food source.

Therefore, at least theoretically, there’s probably a good chance that scout bees could communicate within the hive. Using spatially distant dances and a unique combination of olfactory clues (or their absence) scouts may well be able to recruit other scouts to check likely new nest sites.

All of which would support my view that bait hives provide a useful early warning system for colonies that are in the very earliest stages of swarm preparations … rather than just an indicator that there’s a bivouacked swarm in the vicinity.

But?

All this of course then begs the question … if the scout bees can communicate within the hive, why does the swarm need to bivouac at all?

The bivouac must be a risky stage in the already precarious process of swarming. 80% of wild swarms perish. At the very least it’s subject to the vagaries of the weather. Surely it would be advantageous to stay within the warm, dry hive until a new nest site is identified?

Apple blossom ...

Apple blossom … and signs that a bivouacked swarm perished here

This suggests to me that the bivouac serves additional purposes within the swarming process. A couple of possibilities come to mind:

  • the gravity-independent, sun-orientated waggle dancing 15 on the surface of the bivouac may be a key part of the decision making process, not possible (for reasons that are unclear to me) within the confines of the hive.
  • the bivouac acts to temporally coordinate the swarm. A swarm takes quite a long time to settle at the bivouac. Many bees leave the hive during the excitement of swarming but not all settle in the bivouac. Perhaps it acts as a sorting mechanism to bring together all the bees that are going to relocate, separate from those remaining in the swarmed colony?

Clearly this requires a bit more thought and research.

If your association invites me to discuss swarms and bait hives next winter I might even have an answer.

But, as with so many things to do with bees, knowing that answer will only spawn additional questions 😉


 

Going the distance

I’m going to continue with a topic related to the waggle dance this week.

This is partly so I can write about the science of how bees measure distance to a food source.

But it’s also to encourage those who didn’t read the waggle dance post to visit it. Weirdly it was only read by about 50% of the usual Friday/weekend readership and I suspect (from a couple of emails I received) that the weekly post to subscribers ended up in spam folders 1.

If you remember, the duration of the waggle phase of the dance – the straight-line abdomen-wiggling sashay across the ‘dance floor’ – indicates the distance from the nest to the desirable food source 2. The vigour of the wiggle indicates the quality of the source.

How do bees measure distance?

Karl von Frisch, the first to decode the waggle dance, favoured the so-called ‘energy hypothesis’. In this, the distance to a food source was determined by the amount of energy used on the outbound flight.

Does that seem logical?

Foragers forage randomly, but usually return directly

If correct, foragers would only be able to determine the energy used after their second trip to a food source. This presumes their first trip was longer as they searched the environment for something worth dancing about 3.

This would be an easy thing to test, though I’m not sure it was ever investigated 4.

As it happens, far better brains determined that the energy hypothesis was probably incorrect. Many of these studies explored how gravity influences the distances reported by dancing foragers.

Going up!

Bees use more energy when flying up. For example, when flying from ground level to the top of a tall building, when compared to level flight. Similarly, they use more energy flying if they have small weights attached to them 5.

A series of experiments, nicely reviewed by Harald Esch and John Burns 6, failed to provide good support for the energy hypothesis. There were lots of these studies, involving steep mountains, tall buildings or balloons, between the 1950’s and mid-80’s.

Interesting science, and no doubt it was a lot of fun doing the experiments.

For example, bees flying to a sugar feeder situated on top of a tall building dance to ‘report’ the same distance as bees from the same hive flying to a feeder at ground level adjacent to the same building.

Similarly, foragers loaded with weights do not overestimate the distance to a food source, as would be expected if the energy expended to reach it was being measured 7.

Interesting and entertaining science certainly, but none of it providing compelling support for the energy hypothesis

It’s notable that there is a rather telling sentence from the Esch & Burns review that states “While reading the original papers, one gains the impression that evidence supporting the energy hypothesis was favored over arguments against it”.

Ouch!

Splash landing

Although Von Frisch was a supporter of the energy hypothesis 8 he also published a study that provided evidence for our current understanding of how bees measure distance.

Bees generally don’t like flying long distances over water. Von Frisch provided two equidistant nectar sources, one of which was situated on the other side of a lake.

Bees flying over calm water underestimate distances

On very calm days the bees that flew across the lake under-reported the distance to the feeder. This underestimate was by 20-25% when compared to bees flying to an equidistant feeder overland.

Von Frisch commented “the bee’s estimation of distance is not determined through optical examination of the surface beneath her”.

He assumed that the mirror-like water surface provided no optical input as it contained no visual ‘clues’. After all, one calm patch of water looks much like any other. Von Frisch used this as an argument for the energy hypothesis.

He also noted that the bees generally flew very low over the water surface, often so low that they drowned 🙁

Perhaps these bees were flying dangerously low to try and find optical clues.

Such as their height above the surface?

Or perhaps the distance travelled?

Going with the flow

Having debunked the energy hypothesis, Esch & Burns proposed instead the optic flow hypothesis. This states that “foragers use the retinal image flow of ground motion to gauge feeder distance”.

Imagine optic flow as tripping a little odometer in the bee brain that records distance as her eyes observe the environment flashing past during flight. The clever thing about that is that the environment is variable. It’s not like counting off regularly spaced telegraph poles from a train window.

When flying, environmental objects that are nearby will move across her vision much faster than distant objects. Bees don’t have stereo vision, but instead use this speed of image motion to infer range.

Optic flow – the arrow size indicates the speed with which the object apparently moves, and hence its range

Esch & Burns returned again to tall buildings to provide supporting evidence for their optic flow hypothesis. They trained bees to fly between two tall buildings with 228 metres separating the hive and the feeder 9.

Returning foragers reported that the food source was only 125 metres away.

However, the bees didn’t make a direct flight. Instead they flew at altitude for 30-50 metres, descended to fly much lower, then ascended again to approach the feeder again at altitude.

Esch & Burns experiment to support the optic flow hypothesis

The interpretation here was that the high altitude flight provided insufficient optic flow to measure distance. The bees descend to get the visual input needed to judge distance, but it’s only for part of the flight … hence leading to under-reporting the distance separating the hive and feeder.

Tunnel vision

Jurgen Tautz 10 and colleagues trained bees to forage in a short, narrow tunnel 11. This elegant experiment provided compelling support for the optic flow hypothesis.

The tunnel was ~6 m long and with a cross sectional area of ~200 cm2 – big enough for a bee to fly along, but sufficiently narrow so that the bee would be closer to the ‘walls’ than in normal free flight. The walls and floor of the tunnel had a random visual texture. Only the end of the tunnel facing the hive was open.

The tunnel experiment.

These studies were conducted when the terms round and waggle were used to distinguish the dance induced by food sources <50 m and >50 m respectively from the hive 12. Rather than emphasise the shape of the dance I’ll just describe it as a >50 m or <50 m waggle dance.

‘Tunneling’ bees misreport distances

In the first tunnel experiment (1) the feeder was 35 m from the hive. 85% of dances indicated the feeder was <50 m away. However, when the feeder was moved to the opposite end of the tunnel (2) – still only 41 m from the hive – 90% of the dances indicated the feeder was >50 m away.

To test how the random pattern influenced the perceived distance the scientists used a third tunnel (3) lined with lengthwise stripes. In this instance – despite the feeder position being unchanged from experiment 2 – 90% of the dances indicated the feeder was <50 m away.

The stripes were predicted to ‘work’ in the same way as the smooth lake surface, providing no visual clues.

In the fourth experiment (4) the feeder was 6 m along a randomly patterned tunnel, which was placed just 6 m from the hive. Over 87% of dances indicated that the feeder was >50 m away.

Interpreting the waggle run

In open flight 13 there is usually an excellent correlation between the duration of the waggle run and the distance to a feeder (see the graph below 14 ). By extrapolation, the bees in experiments 2 and 4 ‘thought’ they had flown 230 m and 184 m respectively. In reality they had flown only 41 m and 12 m in these experiments.

Determining distances from waggle dance observation

How could the bees get it so wrong?

Increased optic flow

Tunnel-traversing bees fly just a few centimeters away from the visible ‘environment’.

As a consequence, at the same flight speed, they experience greater optic flow.

If, instead of driving around in your lumbering old van, you pack your hive tool in a Caterham 7 for the trip to the apiary you’d be well aware of what I mean.

Caterham 7 … check out that optic flow … then make another trip to collect the smoker

30 mph in a Toyota Hilux feels very much slower than 30 mph in a Caterham 7. This is largely because visual reference points, like the broken white lines between lanes in the road, appear in and disappear from your field of view much faster … because you’re much closer to them.

Because the tunnel dimensions were known it was possible to calculate the calibration of the bee’s odometer. Classically this would be defined in terms of metres of distance flown generating a particular waggle run length or duration.

These tunnel studies demonstrate that distance flown is not what calibrates the odometer. Instead it’s quantified indirectly in terms of the image motion experienced by the eye. Since environments vary the way to express this is the amount of angular image motion that generates a given duration of waggle.

And, using some mathematical trickery we don’t need to bother with 15, it turns out that this angular motion is only dependent upon distance flown, not the speed of flight.

This is important. Headwinds or tailwinds could change the speed of flight, but not the distance flown 16.

It’s all relative

It’s worth emphasising that the dance followers in experiments 2 (above) should still find the feeder.

The waggle dance would ‘instruct’ them to fly 230 m at the bearing indicated and they’d experience the same visual clues en route.

This means that they should still enter the narrow tunnel and experience increased optic flow because of the encroaching walls. But they’d be experiencing the same optic flow the initial dancing bee had experienced, so would not attempt to fly further down the tunnel.

This means that the optic flow experienced is context dependent. It is related to the environment the bees are foraging in.

This makes sense as the dancing bees and dance followers all occupy the same environment.

How do we know this? 17

Changing the environment

If we change the environment the dance followers search at the wrong distance.

I qualified the statement above when I said that the dance followers should still enter the tunnel and find the feeder.

Actually, most recruits will miss the tunnel entrance – remember it’s smaller that a sheet of A5 paper. At 35 m distance a bee would have to get the bearing correct to about 0.16° to enter the tunnel 18.

So the bees that do not enter the tunnel experience a different environment.

Where do they search for the feeder?

They search at the distance indicated by the waggle duration … so bees that missed the tunnel entrance in experiment 2 (above) would have searched for the feeder 230 m from the hive. Similarly, the dance followers in experiment 4 would have searched 184 m away 19

Context dependent dance calibration

And, finally, the calibration of the odometer depends upon the environment.

Odometer calibration depends upon the environment

If the environment experienced by the dancing bee en route to the feeder in experiments 2 and 4 is different, then it generates a different relationship between waggle run duration and distance.

For example, if one feeder was across a closely mown lawn and the other was across dense shrubby woodland, they would each generate a unique optic flow, so changing the image motion experienced, and hence the waggle run generated.

In the diagram above, you shouldn’t use dance calibration for bees trained to direction A to determine the distance bees going in direction B would forage.

Phew!

Optic flow, waggle dancing and implications for practical beekeeping

None 😉

At least, none that I can think of.

A Caterham 7 isn’t an ideal car for a beekeeper but would be a lot of fun to help you understand optic flow 😉

Most of us keep our bees in mixed environments. Your apiary isn’t situated with a cliff edge on one side and an unbroken prairie on the other. Since the environment is mixed, the waggle dance calibration is not going to be wildly different, whichever way the bees fly off in. You can therefore use an approximate figure of 1 second per kilometre to estimate the the distance at which your bees are foraging, irrespective of the direction they go.


Notes

Most of the referenced studies are at least two decades old. Honey bees have remained a fertile research tool for neurobiologists. Our understanding of honey bee vision continues to improve. However, I cannot discuss any of these more recent studies with reference to optic flow. Anyway, just because they’re old doesn’t make the experiments any less elegant or interesting 🙂

 

The waggle dance

Ask a non-beekeeper what they know about bees and you’ll probably get answers that involve honey or stings.

Press them a little bit more about what they know about other than honey and stings and some will mention the ‘waggle dance’. 

Karl von Frisch

That the waggle dance is such a well-known feature of honey bee biology is probably explained by two (related) things; it involves a relatively complex form of communication in a non-human animal, and because Karl von Frisch – the scientist who decoded the waggle dance – received the Nobel Prize 1 for his studies in 1973.

Von Frisch did not discover the waggle dance. Nicholas Unhoch described the dance at least a century before Von Frisch decoded the movement, and Ernst Spitzner – 35 years earlier still – observed dancing bees and suggested they were communicating odours of food resources available in the environment.

Inevitably, Aristotle also made a contribution. He described flower constancy 2 and suggested that foragers could communicate this to other bees.

Language and communication are important. The development of language in early humans almost certainly contributed to the evolution of our culture, society and technology. Communication in non-human animals, from the chirping of grasshoppers to the singing of whales, is of interest to scientists and non-scientists alike.

It is therefore unsurprising that the ‘dance language’ of honey bees is also of great interest. Although not a ‘language’ in the true sense of the word, Von Frisch described the symbolic language of bees as “the most astounding example of non-primate communication that we know” over 50 years ago. This still applies.

The waggle dance

The waggle dance usually takes place in the dark on the vertical face of a comb in the brood nest, usually close to the nest entrance. The dance is performed by a successful forager i.e. one that has located a good source of pollen, nectar or water, and provides information on the presence, the quality, identity, direction and distance of the source, so enabling nest-mates to find and exploit it.

The dance consists of two phases:

  1. The figure of eight-shaped ‘return phase’ in which the bee circles back, alternately clockwise and anticlockwise, to the start of …
  2. The ‘waggle phase’, which is a short linear run in which the dancer vigorously waggles her abdomen from side to side.

The direction of the food source is indicated by the angle of the waggle phase from gravity i.e. a vertical line down the face of the comb. This angle (α in the figure below) indicates the bearing from the direction of the sun that needs to be followed to reach the food source. 

For example, if the dancer performs a waggle phase vertically down the face of the comb, the food source must be opposite the current position of the sun.

The waggle dance

The distance information is conveyed by the duration of the waggle phase. The longer this run is, the more distant the source. A run of 1 second duration indicates the food source is about 1 kilometre away.

The quality of the food source is indicated by the vigour of the waggling during the waggle phase and the speed with which the return phase is conducted. 

Surely it can’t be that simple?

Yes, it can.

What I’ve described above allows you to interpret the waggle dance sufficiently well to know where your bees are foraging.

Next time you lift a frame from a hive and see a dancing bee, circling around in a little cleared ‘dance floor’ surrounded by a group of attentive workers, try and decode the dance.

Remember that the dance is performed with relation to gravity in the darkened hive. You’re looking to identify the angle from a vertical line up the face of the brood comb to determine the direction from the sun.

Time a few waggle phases (one elephant, two elephants etc.) and you’ll know how far away the food source is.

Really, it’s that simple?

Of course not 😉

The waggle dance was decoded more than half a century ago and remains an active subject for researchers interested in animal communication.

What you’ll miss in your observations is an indication of the type of nectar or pollen resource that the dancing bee is communicating. The dancing worker carries the odour of the food source and may also regurgitate nectar, presumably helping those ‘watching’ (remember, it’s dark … nothing to see here!) determine the type of resource to look for when they leave the hive.

You will also be unable to detect the pulsed thoracic vibrations that the dancing bee produces. These are also indicators of the quality of the food source; better (e.g. higher sucrose content) resources elicit increased pulse duration, velocity amplitude and duty cycle, though the number of pulses is related to the duration of the waggle phase, and so is another potential indicator of distance.

Inevitably, there are also pheromones involved.

There always are 😉

The dancing bee produces two alkanes, tricosane and pentacosane, and two alkenes, Z-(9)-tricosene and Z-(9)-pentacosene. These appear to stimulate foraging activity 3.

But it’s cloudy … or rain stops play … or nighttime

What happens to dancing bees if foraging is interrupted, for example by poor weather or night? 

The dancing bee continues to change the angle of the waggle phase as the sun moves across the sky. This means that a dancing bee will correctly signal the direction to the food source, even if they have not left the hive for several hours.

During their initial orientation flights they learn the sun’s azimuth as a function of the time of day, and use this to compensate for the sun’s time-dependent movement.

Some bees even dance during the night, in which case the watching workers must presumably make their own compensations for the time that has elapsed since the dance 4.

And what happens if the sun is obscured … by clouds, or buildings or dense woodland? How can those directions be followed?

Under these circumstances the foraging bee detects the position of the sun by the pattern of polarised light in the sky. 

Scout bees

The waggle dance is also performed by scout bees on the surface of a bivouacked swarm. In this instance it is used to communicate the quality, direction and distance of a new potential nest site. 

Swarm of bees

Swarm of bees

The intended audience in this instance are other scout bees, rather than the general forager population 5. These scouts use a quorum decision making process to determine the ‘best’ nest site in the area to which the bivouacked swarm eventually relocates.

The shape of the bivouac often lacks a true vertical surface. However, since it’s in the open the dancing bees can orientate the waggle run directly with relation to the sun’s direction, rather than to gravity.

Under experimental conditions the dancing bee can communicate the presence and quality of a food source on a horizontal comb, but – with no reference to gravity – all directional information is lost 6.

The round dance

The duration of the waggle phase is related to the distance from the nest to the food source. Therefore the recognisable waggle dance tends to get difficult to interpret for sources very close to the nest.

It used to be thought that there was a distinct directionless dance (the ’round dance’) for these nearby i.e. 10-40 metres, food sources. However, more recent study 7 suggests that dancers were able to convey both distance and direction information irrespective of the separation of nest and food source. This indicates that bees have just one type of dance for forager recruitment, the waggle dance.

Do all bees communicate using a waggle dance?

There are a very large number of bee species. In the UK alone there are 270 species, 250 of which are solitary.

There’s a clue.

Solitary bees are like me at a disco … they have no one to dance with 🙁

I’ll cut to the chase to help you erase that vision.

The only bees that use the waggle dance are honey bees. These all belong to the genus Apis.

They include our honey bee, the western honey bee (Apis mellifera), together with a further seven species:

  1. Black dwarf honey bee (Apis andreniformis)
  2. Red dwarf honey bee (Apis florea)
  3. Giant honey bee (Apis dorsata)
  4. Himalayan giant honey bee (Apis laboriosa
  5. Eastern honey bee (Apis cerana)
  6. Koschevnikov’s honey bee (Apis koschevnikovi)
  7. Philippine honey bee (Apis nigrocincta)

Dancing and evolution

Dwarf honey bees nest in the open on a branch and dance on the horizontal surface of the nest. The waggle run is orientated ‘towards’ the food source. Apis dorsata is also an open-nesting bee, but forms large vertically-hanging combs. It dances relative to gravity, and indicates the direction by the angle of the waggle run in the same way that A. mellifera does.

The cavity nesting bees, A. cerana, A. mellifera, A. koschevnikovi, and A. nigrocinta produce the most developed form of the dance.

The dances of A. mellifera and A. cerana are sufficiently similar that they can follow and decode the dance of the other.

The complexity of the nest site and the waggle dance reflects the evolution of these bee species. The earliest to evolve (i.e. the most primitive), A. andreniformis and florea, have the simplest nests and the most basic waggle dance. In contrast, the cavity nesting species evolved most recently, form the most complex brood nests and have the most derived waggle dance.

When and why did the waggle dance evolve?

Assuming that the waggle dance did not independently evolve (there’s no evidence it did, and ample evidence due to its similarity between species that it evolved only once) it must have first appeared at least 20 million years ago, when extant honey bee species diverged during the early Miocene.

The ‘why’ it evolved is a bit more difficult to address.

Behavioural changes often arise in response to the environment in which a species evolves.

Bipedalism in non-human primates (like the australopithecines) is hypothesised to have evolved in part due to a reduction in forest cover and the increase in savannah. Apes had to walk further between clumps of trees and bipedalism offered greater travel efficiency.

Perhaps the waggle dance evolved to exploit a particular type or distribution of food reserves?

In this regard it is interesting that the ‘benefit’ of waggle dance communication varies through the season.

If you turn a hive on its side the combs are horizontal 8. Under these conditions the dancing bees can communicate the presence and quality of a food source. However, they cannot communicate its location (either direction or distance).

No directional or distance information is now available

In landmark studies Sherman and Visscher 9 showed that, at certain periods during the season, the absence of this positional information did not affect the weight gain by the hive i.e. the foraging efficiency of the colony.

They concluded that during these periods forage must be sufficiently abundant that simply stimulating foraging was sufficient. Remember those alkanes and alkenes produced by dancing bees that do exactly that?

Tropical habitats

This observation, and some elegant experimental and modelling studies, suggest that dancing is beneficial when food resources are: 

  • sparsely distributed – therefore difficult (and energetically unfavourable) to find by individual scouting
  • clustered or short-lived resources – when it’s gone, it’s gone
  • distributed with high species richness – if there’s a huge range of flowers, which are the most energetically rewarding (sugar-rich) to collect nectar from?

One of the experimental studies that contributed to these conclusions (though there’s still controversy in this area) was the demonstration that waggle dancing was beneficial in a tropical habitat, but not in two temperate habitats. This makes sense, as food resources have different spatiotemporal distribution in these habitats. Tropical habitats are characterised by clustered and short-lived resources.

Therefore the suggestion is that the waggle dance of Apis species evolved, presumable early in the speciation of the genus, in a tropical region where food resources were patchily distributed, available for only limited period and present alongside a wide variety of other (less good) choices.

For example, like individual trees flowering in a forest …

Finally, it’s worth noting that there is evidence that bees that dance are able to successfully exploit food resources further away than would otherwise be expected from their body size.

This also makes sense.

It’s much less risky flying off over the horizon if you know there’s something to collect once you get there 10.


Notes

If you arrived here from my Twitter feed (@The_Apiarist) you’ll have seen the tweet started with the words “Dance like nobody’s watching”, words that are often attributed to Mark Twain. 

The full quote is something like “Dance like nobody’s watching; love like you’ve never been hurt. Sing like nobody’s listening; live like it’s heaven on earth”.

Pretty sound advice.

But it’s not by Mark Twain. It’s actually from a country music song by Susanna Clark and Richard Leigh. This was first released on the Don Williams album Traces in 1987. So only about 90 years out 😉 

Smell the fear

With Halloween just around the corner it seemed appropriate to have a fear-themed post.

How do frightened – or even apprehensive – people respond to bees?

And how do bees respond to them?

Melissophobia is the fear of bees. Like the synonym apiphobia, the word is not in the dictionary 1 but is a straightforward compounding of the Greek μέλισσα or Latin apis (both meaning honey bee) and phobos for fear.

Melissophobia is a real psychiatric diagnosis. Although people who start beekeeping are probably not melissophobic, they are often very apprehensive when they first open a colony.

If things go well this apprehension disappears, immediately or over time as their experience increases.

If things go badly they might develop melissophobia and stop beekeeping altogether.

Even relatively experienced beekeepers may be apprehensive when inspecting a very defensive colony. As I have discussed elsewhere, there are certain times during the season when colonies can become defensive. These include when queenless, during lousy weather or when a strong nectar flow ends.

In addition, some colonies are naturally more defensive than others.

Some could even be considered aggressive, making unprovoked attacks as you approach the hive.

A defensive response is understandable if the colony is being threatened. Evolution over eons will have led to acquisition of appropriate responses to dissuade natural predators such as bears and honey badgers.

I’m always careful (and possibly a little bit apprehensive) when looking closely at a completely unknown colony – such as these hives discovered when walking in the Andalucian hills.

If Carlsberg did apiaries ...

Apiary in Andalucia

How do bees detect things – like beekeepers or bears – that they might need to mount a defensive response against?

Ignore the bear

Bees have four senses; sight, smell, touch and taste. Of these, I’ve briefly discussed sight previously and they clearly don’t touch or taste an approaching bear 2 … so I’ll focus on smell.

Could they use smell to detect the scent of an approaching human or bear that is apprehensive of being stung badly?

Let’s forget the grizzly bear 3 for now. At over 200 kg and standing 2+ metres tall I doubt they’re afraid of anything.

Let’s instead consider the apprehensive beekeeper.

Do bees respond to the smell of a frightened human (beekeeper or civilian)?

This might seem a simple question, but it raises some interesting additional questions.

  • Is there a scent of fear in humans?
  • Can bees detect this smell?
  • Have bees evolved to generate defensive responses to this or similar smells?

If two beekeepers inspect the same colony and one considers them aggressive and the other does not, is that due to the beekeepers ‘smelling’ different?

I don’t know the answers to some of these questions, but it’s an interesting topic to think about the stimuli that bees have evolved to respond to.

The scent of fear

This is the easy bit.

Is there a distinctive scent associated with fear in humans?

The Scream by Edvard Munch (1895 pastel version)

Using some rather unpleasant psychological testing researchers have determined that there is a smell produced in sweat secretions that is associated with fear. Interestingly, the smell alone appears not to be detectable. The female subjects tested 4 were unable to consciously discriminate the smell from a control neutral odour.

However, the ‘fear pheromone’ alone caused changes in facial expression associated with fright and markedly reinforced responses to visual stimuli that induced fear.

Females could respond to the fear pheromone produced by males (and vice versa) and earlier MRI studies (involving significantly less unpleasant experiments) had shown that this smell was alone able to induce changes in the amygdala, the region in the brain associated with emotional processing.

So, there is a scent of fear in humans. We can’t consciously detect it, but that doesn’t make it any less real.

Can bees detect it?

Can bees smell the scent of fear?

This is where things get a lot less certain.

I’m not aware that there have been any studies on whether bees can definitively identify the fear pheromone produced by humans.

To conduct this study in a scientifically-controlled manner you would need to know precisely what the pheromone was. It would then be tested in parallel with one or several irrelevant, neutral or related (but different) compounds. In each instance you would have to identify a response in the bee that indicated the fear pheromone had been detected.

All of which is not possible as we don’t definitely know what the fear pheromone is chemically.

We do know it’s present in the sweat of frightened humans … but that’s about it. This makes the experiment tricky. Comparisons would also have to be made with sweat secretions present in the same 5 human when not frightened.

And what response would you look for? Usually bees are trained to respond in a proboscis extension test. In this a bee extends its proboscis in response to a recognised smell or taste.

But, as none of this has been done, there’s little point in speculating further.

So let’s ask the question the other way round.

Would bees be expected to smell the scent of fear?

Smell is very significant to bees.

They have an extremely sensitive sense of smell, reflected in their ability to detect certain molecules as dilute as one or two parts per trillion. Since many people struggle with visualising what that means it’s like detecting a grain of salt in an Olympic swimming pool 6.

Part of the reason we know that smell is so important to bees is because evolution has provided them with a very large number of odorant receptors.

Odorant receptors are the proteins that detect smells. They bind to chemical molecules from the ‘smell’ and these trigger a cellular response of some kind 7. Different odorant receptors have different specificities, binding and responding to the molecules that are present in one or more odours.

Odorant receptor diversity and sensitivity

Bees have 170 odorant receptors, more than three times the number in fruit flies, and double that in mosquitoes. Smell is clearly very important to bees 8.

This is perhaps not surprising when you consider the role of odours within the hive. These include the queen and brood pheromones and the chemicals used for kin recognition 9.

In addition, bees are able to find and use a very wide range of plants as sources of pollen and nectar and smell is likely to contribute to this in many ways.

Finally, we know that bees can detect and respond to a wide range of other smells. Even those present at very low levels which they may not have been exposed to previously. For example Graham Turnbull and his research team in St Andrews, in collaborative studies with Croatian beekeepers, are training bees to detect landmines 10 from the faintest ‘whiff’ of TNT they produce. This deserves a post of its own.

So, while we don’t know that bees could detect a fear pheromone, there’s a good chance that they should be able to.

Evolution of defensive responses

We’re back to some rather vague arm waving here I’m afraid.

In a rather self-fulfilling manner we don’t know if bees have evolved a defensive response to the fear pheromone of humans as – for reasons elaborated above – we don’t actually know whether they do respond to the fear pheromone.

We could again ask this question in a slightly different way.

Might bees be expected to have evolved a defensive response to the fear pheromone?

Long before we developed the poly nuc or the fiendishly clever Flow Hive, humans have been attracted by honey and have exploited bees to harvest it.

The ancient Egyptians kept bees in managed hives over 5000 years ago.

However, we can be reasonably certain that humans provided suitable nesting sites (which we’d now call bait hives) to attract swarms from wild colonies well before that.

But we’ve exploited bees for tens or hundreds of thousands of years more than that.

The ‘Woman(Man) of Bicorp” honey gathering (c. 8000 BC)

There are examples of Late Stone Age (or Upper Paleolithic c. 50,000 to 10,000 years ago) rock art depicting bees and honey from across the globe, with some of the most famous being in the Altamira (Spain) cave drawings from c. 25,000 years ago.

Survival of the fittest

And the key thing about many of these interactions with honey bees is that they are likely to have been rather one-sided. Honey hunting tends to be destructive and results in the demise of the colony – the tree is felled, the brood nest is ripped apart, the stores (and often the brood) are consumed.

None of this involves carefully caging the queen in advance 🙁

This is a strong selective pressure.

Colonies that responded earlier or more strongly to the smell of an apprehensive approaching hunter gatherer might be spared. These would survive to reproduce (swarm). Literally, the survival of the fittest.

All of this would argue that it might be expected that bees would evolve odorant receptors capable of detecting the fear pheromone of humans.

There’s no fire without smoke

There are (at least) two problems with this reasoning.

The first problem is that humans acquired the ability to use fire. And, as the idiom almost says, there’s no fire without smoke. Humans were regularly using fire 150-200,000 years ago, with further evidence stretching back at least one million years that pre-humans (Homo erectus) used fire.

And, if they were using fire you can be sure they would be using smoke to ‘calm’ the bees millenia before being depicted doing so in Egyptian hieroglyphs ~5,000 years ago.

It seems reasonable to expect that the use of smoke would mask the detection of fear pheromones, in much the same way that it masks the alarm pheromone when you give them a puff from your trusty Dadant.

The other problem is that it might be expected that the Mesolithic honey hunters had probably ‘got the job’ precisely because they weren’t afraid of bees. In extant hunter gatherer communities it’s known that there are specialists that have a particular aptitude for the role. Perhaps these beekeepersrobbers produce little of no fear pheromone in the first place?

What about other primates?

It’s well know that non-human primates (NHP’s), like chimpanzees and bonobo, love honey. They love it so much that they are responsible for an entire research area studying tool use by chimps.

Bonobo ‘fishing’ for termites using a tool (I couldn’t find a suitable one robbing honey)

Perhaps NHP’s produce a fear pheromone similar to that of humans? Since they haven’t learned to use fire (and they are very closely related to humans) bees may have evolved to respond to primate fear pheromone(s), and – by extension – to those of humans.

However, chimpanzees and related primates prefer to steal honey from stingless bees like Meliponula bocandei. The only information I could find suggested they avoided Apis mellifera, or “used longer sticks as tools“.

Perhaps not such a strong selective pressure after all …

More arm waving

A lot of the above is half-baked speculation interspersed with a smattering of evolutionary theory.

Bees clearly respond in different ways to different beekeepers. I’ve watched beekeepers retreat from a defensive colony which – later on the same training day – were beautifully calm when inspected by a different beekeeper.

Trainee beekeepers

Trainee beekeepers

Although this might have been due to differences in the production of fear pheromones, it’s clear that the bees are also using other senses to detect potential threats to the colony.

Look carefully at how outright beginners, intermediate and expert beekeepers move their hands when inspecting a colony.

The tyro goes slow and steady. Everything ‘by the book’. Not calm, but definitely very controlled.

The expert goes a lot faster. However, there’s no banging frames down, there are no sudden movements, the hands move beside the brood box rather than over it. Calm, controlled and confident.

In contrast, although the “knowing just enough to be dangerous” intermediate beekeeper is confident, they are also rushed and a bit clumsy. Hands move back and forwards over the box, movements are rapid, frames are jarred … or dropped. A bee sneaks inside the cuff and stings the unprotected wrist. Ouch!

“That’s an aggressive colony. Better treat it with care.”

You see what I mean about arm waving?

I strongly suspect movement and vibration trigger defensive responses to a much greater extent than the detection of fear pheromones in humans (if they’re detected at all).

Closing thoughts

You’ll sometimes read that bees respond badly to aftershave or perfumes. This makes sense to me only if the scent resembles one that the bees have evolved a defensive response against.

Don’t go dabbing Parfum de honey badger behind your ears before starting the weekly inspection.

Mellivora capensis – the honey badger. Believe me, you’re not worth it.

But why would they react aggressively to an otherwise unknown smell?

After all, they experience millions of different – and largely harmless – smells every day. Bees inhabit an environment that is constantly changing. One more unknown new scent does not immediately indicate danger. There would be an evolutionary cost to generating a defensive response to something that posed no danger.

And a final closing thought for you to dwell on …

Humans have probably been using fire to suppress honey bee colony aggression for hundreds of thousands of years.

Why haven’t bees evolved defensive responses to the smell of smoke? 11

Happy Halloween 🙂