Category Archives: Drifting and robbing

A virus that changes bee behaviour

Particle physicists might not agree, but I think that evolution is the most powerful force in the universe. It is responsible for the fabulous diversity of life, for everything from the 6,000,000 kg Pando clonal colony of quaking aspen covering 43 hectares of the Fishlake National Forest in Utah, to the teeniest of tiniest of viruses.

As a microbiologist I’m acutely aware of the role evolution has played in the genetic arms race between hosts and pathogens. This is what is responsible for the multi-faceted immune system higher organisms carry – the antibodies, the lymphocytes, the complement and interferon responses, and everything else.

In turn, the fast replicating bacteria and viruses have evolved countermeasures to subvert these immune mechanisms, to switch them off entirely or to decoy them into targeting the wrong thing. This ‘arms race’ has gone on since well before the evolution of multicellular organisms (~600 million years ago) … and continues unabated.

Evolution is powerful for one simple reason; if a particular genetic combination 1 ‘works’ it will be passed on to the progeny. If a virus evolves a way to resist the immune response of the host, or to spread between hosts more efficiently, then the trait will be inherited.

Molecular mechanisms and behavioural changes

Some of changes work at the molecular level, invisible without exquisitely sensitive in vitro analysis; protein A binds to protein B and, in doing so, stops protein B from doing whatever it should have be doing. These are important but often very subtle.

Rabies: Slaying a mad dog, 1566 illustration from Wellcome Images

Other changes are far more obvious. Take rabies for example (or don’t, it’s not recommended as it has a near-100% case fatality rate) … the primary host of the rabies virus are carnivorous mammals. Infection causes gross behavioural changes that facilitate virus transmission. The animal becomes bolder and much more aggressive, resulting in virus transmission through biting.

Recent studies have elegantly demonstrated that this (also) is an example of protein A binding to protein B at the molecular level, it’s just that the phenotype 2 is very much more marked.

A protein on the surface of the virus resembles a snake venom toxin and has the ability to bind to nicotinic acetylcholine receptors present in the central nervous system of the mammalian host. These receptors ‘do what they say on the tin’ and bind the neurotransmitter acetylcholine. If the virus protein binds the receptor the response to acetylcholine is blunted and this, in turn, leads to hyperactivity, one of the key behavioural responses caused by rabies viruses.

That’s enough about mad dogs.

If virus-induced behavioural changes are so obvious, why haven’t lots of different examples already been identified and characterised?


Part of the problem is the blurring of distinctions between overt behavioural changes and the direct symptoms induced due to the virus replicating.

Human rhinovirus, the aetiological agent of the common cold, causes upper respiratory tract infections. You get a runny nose and you sneeze a lot.


Your behaviour changes.

However, it’s generally accepted that the sneezing and runny nose are a result of the physiological response to infection, rather than a virus-induced behavioural response to facilitate transmission.

It’s worth noting that all that “stuff” that comes out of your nose contains infectious virus, so it’s perhaps an artificial distinction between the general symptoms of sickness and evolutionarily-selected host behavioural changes caused by the virus.

Which in a roundabout way …

… allows me to finally introduce the topic of bee viruses that cause host behavioural changes involved in their transmission.

Or, rather, one bee virus that does this … though I’m certain that there will be more.

Israeli Acute Paralysis Virus (IAPV) is an RNA virus transmitted horizontally by direct contact between bees, or while feeding on developing pupae, by the parasitic mite Varroa destructor. It was implicated as a causative agent of Colony Collapse Disorder (CCD), though really compelling evidence supporting it as the primary cause never materialised.

It’s a virus UK beekeepers should be aware of, but unworried by, as it is extremely rare in the UK.

A recent paper has shown two behavioural changes in response to IAPV infection in honey bees. One of them – that facilitates horizontal transmission between colonies – is also partially explained at the molecular level.

The paper was published a couple of months ago:

Geffre et al., (2020) Honey bee virus causes context-dependent changes in host social behavior. Proc. Natl. Acad. Sci. USA 117:10406-10413. 3

I’m going to focus on the results, rather than the methods, though the methods are rather cool. They used barcoded bees to allow the automated image analysis of every bee in a colony for some of the studies where they had introduced known IAPV infected individuals.

Responses of nestmates to IAPV infected bees

Imagine watching a few hundred waggle dances and being able to recount the position, distance and response of every bee ‘watching’ 4 the dance, and then being able to summarise the results.

Over five days.


Including nights (and yes, bees do still waggle dance at night – a subject for the future).

The scientists orally infected groups of 30 bees with a sub-lethal dose of IAPV, marked them and released them into an observation hive. They then recorded their movements around the hive and their interactions with other bees in the colony. In particular, they focussed on trophallaxis interactions where one bee ‘feeds’ another.

Trophallaxis is also considered to be a method of communication in the hive and has been implicated in disease transmission.

The authors love their whisker plots and statistical analysis.

Who doesn’t? 😉

However, they generally make for rather underwhelming images in a bee blog for entertaining reading. Here .. see what I mean …

Number of trophallaxis interactions per hour.

Suffice to say that the results obtained were statistically significant.

They showed that the infected bees in the colony actually moved about the colony more than their nestmates. Conversely, they were engaged in fewer trophallaxis interactions i.e. it appeared as though they were being ‘ignored’ by their nestmates.

Were they really being ignored altogether or did their nestmates approach them, detect something was amiss and move away?


Antennation is the mechanism by which bees recognise nestmates. They use the sensitive chemoreceptors on their antenna to detect cuticular hydrocarbons (CHC) which are distinctive between bees from different hives.

Antennation is a precursor to trophallaxis.

After all, bees do not want to feed a foreigner, or exchange chemicals involved in communications, or even potentially risk being exposed to a new pathogen.

Good as the barcoding and camera system is, it’s not good enough to record antennation within the observation hive. To do this they manually 5 recorded antennation events between IAPV-infected bees and nestmates in cages in the laboratory 6.

In these studies IAPV-infected bees were engaged in the same number of antennation events as control bees. This strongly suggests that the nestmate could detect there was something ‘wrong’ with the IAPV-infected individuals. In support of this conclusion, the authors also demonstrated that bees inoculated with a double stranded RNA (dsRNA) stimulator of the honey bee immune response were also also antennated equally, but engaged in less trophallaxis interactions.

Therefore, these studies appear to show that nestmates exhibit a behavioural response to IAPV-infected bees (and bees with elevated immune responses, recapitulating their response to pathogen infection) that is likely to be protective, reducing the transmission of horizontally acquired viruses.

It’s worth noting two things here.

  1. There were no virus transmission studies conducted. It’s assumed that the lack of trophallaxis reduces virus transmission. That still needs to be demonstrated.
  2. This response is not induced by the virus on the host. It’s a response by nestmates of the host to virus infected individuals (or individuals that present as ‘sick’). As such it’s not the same as the rabies example I started this post with.

Virus-induced behavioural responses

But do the IAPV-infected bees behave differently when they come into contact with other bees who are not their nestmates?

After all, IAPV is a pathogenic virus and its continuing presence within a population (not just a single hive) depends upon it being spread from hive to hive.

For a highly pathogenic virus this is very important. If you spread from bee to bee within a hive and kill the lot you also go extinct … this partly explains the mechanism by which highly virulent viruses become less virulent over time.

But back to IAPV. What happens when IAPV-inoculated bees interact with bees from a different hive?

For example, what would happen if they drifted from one hive to another in a densely populated apiary? Drifting is a significant contributor to the spread of bees between adjacent colonies – studies show that 1% of marked bees drift to adjacent hives over a 3 day window. This partially accounts for the genetic mix of workers (up to 40% are unrelated to the queen that heads the colony) in a hive, a fact generally unappreciated by beekeepers.

The authors first showed that IAPV-infected bees could apparently leave and return to the hive with a similar frequency as uninfected foragers. Their flying was not compromised.

They then resorted again to recording interactions in the laboratory between IAPV-infected bees or control dsRNA-inoculated bees and workers from a different hive.

This was where it gets particularly interesting.

Hello stranger

The dsRNA-immunostimulated bees (remember, these induce a generalised immune response characteristic of a ‘sick’ bee) were treated aggressively by unmatched workers from a different hive.

In contrast, the IAPV-infected bees (which were ‘sick’ and would have been undergoing immunestimulation caused by the IAPV infection) experienced significantly less aggression than both uninoculated workers (which induced an intermediate response) and the dsRNA-inoculated.

This strongly suggests that IAPV is somehow able to modulate the appearance or behaviour (and one often determines the other) of the host to make it more acceptable to an unmatched worker.

They extended this study to conduct “field-based assays at the entrances of three normally managed honey bee colonies”, monitoring whether IAPV-infected bees were more likely to be accepted by the guard bees at the entrance of the hive.

They were. The IAPV-infected bees received a less aggressive reception and/or entered the hives much more easily than the controls.

But what about proteins A and B?

Good question.

The behavioural alterations described above must be explainable in terms of the molecular changes that IAPV induces in the bees. By that I mean that the virus must make, or induce the making of, a chemical or protein or other molecule, the presence of which explains their acceptance by the foreign guard bees.

And the obvious candidates are the cuticular hydrocarbons (CHC) that are recognized during antennation, which I introduced earlier.

And here the story leaves us with some tantalising clues, but no definitive answer.

The scientists demonstrate that there were marked differences between the CHC profile of IAPV-infected and control bees. Again, they used their favoured whisker plots to show this, but collated all of the CHC data into an even more difficult to explain scatter plot of linear discriminant analysis.

CHC profiles (relative abundance) shown using linear discriminant analysis.

The key take home message here is that for each of the CHC’s analysed there were differences in both the quality and relative abundance between the control bees, bees immunestimulated with dsRNA and the IAPV-infected bees.

These differences were so marked that you can see distinct clustering of points in the analysis above … these bees ‘look’ 7 different to the guard bees that antennate them.

This is a great story.

It’s as yet incomplete. To complete the understanding we will need to know which of those CHC’s, or which combination, when suppressed (or overrepresented) induce the guard bees to say “Welcome, step this way … “.

We’ll then of course need to find out how IAPV induces the change in CHC profile, which takes us right back to protein A and protein B again.

Ever the pedant

Much as I like this science I’d perhap argue that, again, the virus isn’t directly inducing a behavioural change in the host.

What it’s doing is inducing a behavioural change in the response to the infected host (by the guard bee). So perhaps this again isn’t quite the same as the rabies example we kicked off with.

A behavioural change in the host might include IAPV-infected bees drifting more, or drifting further. Alternatively, perhaps a colony with widespread IAPV infection could more easily indulge in robbing neighbouring colonies as they would experience less aggression from guard bees.

Smaller is better ...

Reduced entrance to prevent robbing …

I can see immediate evolutionary benefits to a virus that induced these types of behavioural changes. It’s not an original idea … the late Ingemar Fries suggested it in a paper two decades ago 8.

I’m also certain that researchers are looking for evidence supporting these types of directly-induced behavioural changes caused by viral pathogens in honey bees.

All religion, my friend, is simply evolved out of fraud, fear, greed, imagination, and poetry

Edgar Allen Poe may or may not have said this.

However, while we’re on the thorny subject of pathogen-induced behavioural changes in the host, it might be worth mentioning a couple of more controversial areas in which it has been proposed.

In the snappily titled paper “Assortative sociality, limited dispersal, infectious disease and the genesis of the global pattern of religion diversity” Fincher and Thornhill argue 9 that the wide diversity of religions in the tropics (compared to temperate regions) is driven by infectious disease selecting for three anti-contagion behaviours; in-group assortative sociality; out-group avoidance; and limited dispersal. It’s an interesting idea and I’m pleased I don’t have to test it experimentally. Their argument is that these three behavioural changes select for fractionation, isolation and diversification of the original culture … and hence the evolution of religions.

Conversely, perhaps microorganisms induce religious behaviours (rather than religion per se) that facilitate their transmission. This is exemplified in the entertainingly titled paper “Midichlorians – the biomeme hypothesis: is there a microbial component to religious rituals?” by Panchin et al., (2014). They argue that microbes – and they are really thinking about the gut microbiota here – might be able to influence their hosts (humans) to gather for religious rituals at which both ideas (memes) and infections are more easily transmitted.

Perhaps something to think about when mindlessly spinning out all that summer honey in the next few weeks?

Party, party

I think it’s fair to say that both the papers in the section above have some way to go until they achieve mainstream acceptance … if they ever do.

Furthermore, the general area in which parasites, bacteria and viruses, induce changes in the behaviour of their hosts’ is really in its infancy. We are aware of a lot of behavioural changes, but few are understood at the molecular level 10. As such, we often don’t know whether the association is correlative or causative.

Evolution is certainly a powerful enough selective force to ensure that even extremely subtle benefits to the pathogen may become a genetically-fixed feature of the complex interaction it has with the host.

Respiratory viruses, such as the common cold, Covid-19 and influenza infect millions of people globally and are readily transmitted by direct or indirect contact.

That’s why most of the readers of this post have a face mask nearby and a bottle of hand sanitizer ‘at the ready’. Or should.

Direct transmission benefits the virus as it does not have to survive on a door handle, milk bottle or petrol filling pump.

But direct transmission requires that people meet and are in close contact.

And a paper 10 years ago demonstrated that infection with influenza virus resulted in increased social interactions in the 48 hours post-exposure, compared with the same period pre-exposure 11.

It’s amazing what viruses can do … or might do … or (just look around you) are doing.


Darwinian beekeeping

A fortnight ago I reviewed the first ten chapters of Thomas Seeley’s recent book The Lives of Bees. This is an excellent account of how honey bees survive in ‘the wild’ i.e. without help or intervention from beekeepers.

Seeley demonstrates an all-too-rare rare combination of good experimental science with exemplary communication skills.

It’s a book non-beekeepers could appreciate and in which beekeepers will find a wealth of entertaining and informative observations about their bees.

The final chapter, ‘Darwinian beekeeping’, includes an outline of practical beekeeping advice based around what Seeley (and others) understand about how colonies survive in the wild.


The chapter starts with a very brief review of about twenty differences between wild-living and managed colonies. These differences have already been introduced in the preceding chapters and so are just reiterated here to set the scene for what follows.

The differences defined by Seeley as distinguishing ‘wild’ and ‘beekeepers’ colonies cover everything from placement in the wider landscape (forage, insecticides), the immediate environment of the nest (volume, insulation), the management of the colony (none, invasive) and the parasites and pathogens to which the bees are exposed.

Some of the differences identified are somewhat contrived. For example, ‘wild’ colonies are defined fixed in a single location, whereas managed colonies may be moved to exploit alternative forage.

In reality I suspect the majority of beekeepers do not move their colonies. Whether this is right or not, Seeley presents moving colonies as a negative. He qualifies this with studies which showed reduced nectar gathering by colonies that are moved, presumably due to the bees having to learn about their new location.

However, the main reason beekeepers move colonies is to exploit abundant sources of nectar. Likewise, a static ‘wild’ colony may have to find alternative forage when a particularly good local source dries up.

If moving colonies to exploit a rich nectar source did not usually lead to increased nectar gathering it would be a pretty futile exercise.

Real differences

Of course, some of the differences are very real.

Beekeepers site colonies close together to facilitate their management. In contrast, wild colonies are naturally hundreds of metres apart 1. I’ve previously discussed the influence of colony separation and pathogen transmission 2; it’s clear that widely spaced colonies are less susceptible to drifting and robbing from adjacent hives, both processes being associated with mite and virus acquisition 3.

Abelo poly hives

50 metres? … I thought you said 50 centimetres. Can we use the next field as well?

The other very obvious difference is that wild colonies are not treated with miticides but managed colonies (generally) are. As a consequence – Seeley contends – beekeepers have interfered with the ‘arms race’ between the host and its parasites and pathogens. Effectively beekeepers have ‘weaken[ed] the natural selection for disease resistance’.

Whilst I don’t necessarily disagree with this general statement, I am not convinced that simply letting natural selection run its (usually rather brutal) course is a rational strategy.

But I’m getting ahead of myself … what is Darwinian beekeeping?

Darwinian beekeeping

Evolution is probably the most powerful force in nature. It has created all of the fantastic wealth of life forms on earth – from the tiniest viroid to to the largest living thing, Armillaria ostoyae 4. The general principles of Darwinian evolution are exquisitely simple – individuals of a species are not identical; traits are passed from generation to generation; more offspring are born than can survive; and only the survivors of the competition for resources will reproduce.

I emphasised ‘survivors of the competition’ as it’s particularly relevant to what is to follow. In terms of hosts and pathogens, you could extend this competition to include whether the host survives the pathogen (and so reproduces) or whether the pathogen replicates and spreads, but in doing so kills the host.

Remember that evolution is unpredictable and essentially directionless … we don’t know what it is likely to produce next.

Seeley doesn’t provide a precise definition of Darwinian beekeeping (which he also terms natural, apicentric or beefriendly beekeeping). However, it’s basically the management of colonies in a manner that more closely resembles how colonies live in the wild.

This is presumably unnnatural beekeeping

In doing so, he claims that colonies will have ‘less stressful and therefore more healthful’ lives.

I’ll come back to this point at the end. It’s an important one. But first, what does Darwinian mean in terms of practical beekeeping?

Practical Darwinian beekeeping

Having highlighted the differences between wild and managed colonies you won’t be surprised to learn that Darwinian beekeeping means some 5 or all of the following: 6

  • Keep locally adapted bees – eminently sensible and for which there is increasing evidence of the benefits.
  • Space colonies widely (30-50+ metres) – which presumably causes urban beekeepers significant problems.
  • Site colonies in an area with good natural forage that is not chemically treated – see above.
  • Use small hives with just one brood box and one super – although not explained, this will encourage swarming.
  • Consider locating hives high off the ground – in fairness Seeley doesn’t push this one strongly, but I could imagine beekeepers being considered for a Darwin Award if sufficient care wasn’t taken.
  • Allow lots of drone brood – this occurs naturally when using foundationless frames.
  • Use splits and the emergency queen response for queen rearing i.e. allow the colony to choose larvae for the preparation of new queens – I’ve discussed splits several times and have recently posted on the interesting observation that colonies choose very rare patrilines for queens.
  • Refrain from treating with miticides – this is the biggy. Do not treat colonies. Instead kill any colonies with very high mite levels to prevent them infesting other nearby colonies as they collapse and are robbed out.

Good and not so good advice

A lot of what Seeley recommends is very sound advice. Again, I’m not going to paraphrase his hard work – you should buy the book and make your own mind up.

Sourcing local bees, using splits to make increase, housing bees in well insulated hives etc. all works very well.

High altitude bait hive …

Some of the advice is probably impractical, like the siting of hives 50 metres apart. A full round of inspections in my research apiary already takes a long time without having to walk a kilometre to the furthest hive.

The prospect of inspecting hives situated at altitude is also not appealing. Negotiating stairs with heavy supers is bad enough. In my travels I’ve met beekeepers keeping hives on shed roofs, accessed by a wobbly step ladder. An accident waiting to happen?

And finally, I think the advice to use small hives and to cull mite-infested colonies is poor. I understand the logic behind both suggestions but, for different reasons, think they are likely to be to the significant detriment of bees, bee health and beekeeping.

Let’s deal with them individually.

Small hives – one brood and one super

When colonies run out of space for the queen to lay they are likely to swarm. The Darwinian beekeeping proposed by Seeley appears to exclude any form of swarm prevention strategy. Hive manipulation is minimal and queens are not clipped.

They’ll run out of space and swarm.

Even my darkest, least prolific colonies need more space than the ~60 litres offered by a brood and super.

Seeley doesn’t actually say ‘allow them to swarm’, but it’s an inevitability of the management and space available. Of course, the reason he encourages it is (partly – there are other reasons) to shed the 35% of mites and to give an enforced brood break to the original colony as it requeens.

These are untreated colonies. At least when starting the selection strategy implicit in Darwinian beekeeping these are likely to have a very significant level of mite infestation.

These mites, when the colony swarms, disappear over the fence with the swarm. If the swarm survives long enough to establish a new nest it will potentially act as a source of mites far and wide (through drifting and robbing, and possibly – though it’s unlikely as it will probably die – when it subsequently swarms).

A small swarm

A small swarm … possibly riddled with mites

Thanks a lot!

Lost swarms – and the assumption is that many are ‘lost’ – choose all sorts of awkward locations to establish a new nest site. Sure, some may end up in hollow trees, but many cause a nuisance to non-beekeepers and additional work for the beekeepers asked to recover them.

In my view allowing uncontrolled swarming of untreated colonies is irresponsible. It is to the detriment of the health of bees locally and to beekeepers and beekeeping.

Kill heavily mite infested colonies

How many beekeepers reading this have deliberately killed an entire colony? Probably not many. It’s a distressing thing to have to do for anyone who cares about bees.

The logic behind the suggestion goes like this. The colony is heavily mite infested because it has not developed resistance (or tolerance). If it is allowed to collapse it will be robbed out by neighbouring colonies, spreading the mites far and wide. Therefore, tough love is needed. Time for the petrol, soapy water, insecticide or whatever your choice of colony culling treatment.

In fairness to Seeley he also suggests that you could requeen with known mite-resistant/tolerant stock.

But most beekeepers tempted by Darwinian ‘treatment free’ natural beekeeping will not have a queen bank stuffed with known mite-resistant mated queens ‘ready to go’.

But they also won’t have the ‘courage’ to kill the colony.

They’ll procrastinate, they’ll prevaricate.

Eventually they’ll either decide that shaking the colony out is OK and a ‘kinder thing to do’ … or the colony will get robbed out before they act and carpet bomb every strong colony for a mile around.

Killing the colony, shaking it out or letting it get robbed out have the same overall impact on the mite-infested colony, but only slaying them prevents the mites from being spread far and wide.

And, believe me, killing a colony is a distressing thing to do if you care about bees.

In my view beefriendly beekeeping should not involve slaughtering the colony.

Less stress and better health

This is the goal of Darwinian beekeeping. It is a direct quote from final chapter of the book (pp286).

The suggestion is that unnatural beekeeping – swarm prevention and control, mite management, harvesting honey (or beekeeping as some people call it 😉 ) – stresses the bees.

And that this stress is detrimental for the health of the bees.

I’m not sure there’s any evidence that this is the case.

How do we measure stress in bees? Actually, there are suggested ways to measure stress in bees, but I’m not sure anyone has systematically developed these experimentally and compared the stress levels of wild-living and managed colonies.

I’ll explore this topic a bit more in the future.

I do know how to measure bee health … at least in terms of the parasites and pathogens they carry. I also know that there have been comparative studies of managed and feral colonies.

Unsurprisingly for an unapologetic unnatural beekeeper like me ( 😉 ), the feral colonies had higher levels of parasites and pathogens (Catherine Thompson’s PhD thesis [PDF] and Thompson et al., 2014 Parasite Pressures on Feral Honey Bees). By any measurable definition these feral colonies were less healthy.

Less stress and better health sounds good, but I’m not actually sure it’s particularly meaningful.

I’ll wrap up with two closing thoughts.

One of the characteristics of a healthy and unstressed population is that it is numerous, productive and reproduces well. These are all characteristics of strong and well-managed colonies.

Finally, persistently elevated levels of pathogens are detrimental to the individual and the population. It’s one of the reasons we vaccinate … which will be a big part of the post next week.


Midseason mite management

The Varroa mite and the potpourri of viruses it transmits are probably the greatest threat to our bees. The number of mites in the colony increases during the spring and summer, feeding and breeding on sealed brood.

Pupa (blue) and mite (red) numbers

In early/mid autumn mite levels reach their peak as the laying rate of the queen decreases. Consequently the number of mites per pupa increases significantly. The bees that are reared at this time of year are the overwintering workers, physiologically-adapted to get the colony through the winter.

The protection of these developing overwintering bees is critical and explains why an early autumn application of a suitable miticide is recommended … or usually essential.

And, although this might appear illogical, if you treat early enough to protect the winter bees you should also treat during a broodless period in midwinter. This is necessary because mite replication goes on into the autumn (while the colony continues to rear brood). If you omit the winter treatment the colony starts with a higher mite load the following season.

And you know what mites mean

Mites in midseason

Under certain circumstances mite levels can increase to dangerous levels 1 much earlier in the season than shown in the graph above.

What circumstances?

I can think of two major reasons 2. Firstly, if the colony starts the season with higher than desirable mite levels (this is why you treat midwinter). Secondly, if the mites are acquired by the colony from other colonies i.e. by infested bees drifting between colonies or by your bees robbing a mite infested colony.

Don’t underestimate the impact these events can have on mite levels. A strong colony robbing out a weak, heavily infested, collapsing colony can acquire dozens of mites a day.

The robbed colony may not be in your apiary. It could be a mile away across the fields in an apiary owned by a treatment-free 3 aficionado or from a pathogen-rich feral colony in the church tower.

How do you identify midseason mite problems?

You need to monitor mite levels, actively and/or passively. The latter includes periodic counts of mites that fall through an open mesh floor onto a Varroa board. The National Bee Unit has a handy – though not necessarily accurate – calculator to determine the total mite levels in the colony based on the Varroa drop.

Out, damn'd mite ...

Out, damn’d mite …

Don’t rely on the NBU calculator. A host of factors are likely to influence the natural Varroa drop. For example, if the laying rate of the queen is decreasing because there’s no nectar coming in there will be fewer larvae at the right stage to parasitise … consequently the natural drop (which originates from phoretic mites) will increase.

And vice versa.

Active monitoring includes uncapping drone brood or doing a sugar roll or alcohol wash to dislodge phoretic mites.

Overt disease

But in addition to looking for mites you should also keep a close eye on workers during routine inspections. If you see bees showing obvious signs of deformed wing virus (DWV) symptoms then you need to intervene to reduce mite levels.

High levels of DWV

High levels of DWV …

During our studies of DWV we have placed mite-free 4 colonies into a communal apiary. Infested drone cells were identified during routine uncapping within 2 weeks of our colony being introduced. Even more striking, symptomatic workers could be seen in the colony within 11 weeks.

Treatment options

Midseason mite management is more problematic than the late summer/early autumn and midwinter treatments.

Firstly, the colony will (or should) have good levels of sealed brood.

Secondly, there might be a nectar flow on and the colony is hopefully laden with supers.

The combination of these two factors is the issue.

If there is brood in the colony the majority (up to 90%) of mites will be hiding under the protective cappings feasting on sealed pupae.

Of course, exactly the same situation prevails in late summer/early autumn. This is why the majority of approved treatments – Apistan (don’t), Apivar, Apiguard etc. – need to be used for at least 4-6 weeks. This covers multiple brood cycles, so ensuring that the capped Varroa are released and (hopefully) slaughtered.

Which brings us to the second problem. All of those named treatments should not be used when there is a flow on or when there are supers on the hive. This is to avoid tainting (contaminating) the honey.

And, if you think about it, there’s unlikely to be a 4-6 week window between early May and late August during which there is not a nectar flow.


The only high-efficacy miticide approved for use when supers are present is MAQS 5.

The active ingredient in MAQS is formic acid which is the only miticide capable of penetrating the cappings to kill Varroa in sealed brood 6. Because MAQS penetrates the cappings the treatment window is only 7 days long.

I have not used MAQS and so cannot comment on its use. The reason I’ve not used it is because of the problems many beekeepers have reported with queen losses or increased bee mortality. The Veterinary Medicines Directorate MAQS Summary of the product characteristics provides advice on how to avoid these problems.

Kill and cure isn’t the option I choose 😉 7

Of course, many beekeepers have used MAQS without problems.

So, what other strategies are available?

Oxalic acid Api-Bioxal

Many beekeepers these days – if you read the online forums – would recommend oxalic acid 8.

I’ve already discussed the oxalic acid-containing treatments extensively.

Importantly, these treatments only target phoretic mites, not those within capped cells.

Trickled oxalic acid is toxic to unsealed brood and so is a poor choice for a brood-rearing colony.

Varroa counts

In contrast, sublimated (vaporised) oxalic acid is tolerated well by the colony and does not harm open brood. Thomas Radetzki demonstrated it continued to be effective for about a week after administration, presumably due to its deposition on all internal surfaces of the hive. My daily mite counts of treated colonies support this conclusion.

Consequently beekeepers have empirically developed methods to treat brooding colonies multiple times with vaporised oxalic acid Api-Bioxal to kill mites released from capped cells.

The first method I’m aware of published for this was by Hivemaker on the Beekeeping Forum. There may well be earlier reports. Hivemaker recommended three or four doses at five day intervals if there is brood present.

This works well 9 but is it compatible with supers on the hive and a honey flow?

What do you mean by compatible?

The VMD Api-Bioxal Summary of product characteristics 10 specifically states “Don’t treat hives with super in position or during honey flow”.

That is about as definitive as possible.

Another one for the extractor ...

Another one for the extractor …

Some vapoholics (correctly) would argue that honey naturally contains oxalic acid. Untreated honey contains variable amounts of oxalic acid; 8-119 mg/kg in one study 11 or up to 400 mg/kg in a large sample of Italian honeys according to Franco Mutinelli 12.

It should be noted that these levels are significantly less than many vegetables.

In addition, Thomas Radetzki demonstrated that oxalic acid levels in spring honey from OA vaporised colonies (the previous autumn) were not different from those in untreated colonies. 

Therefore surely it’s OK to treat when the supers are present?

Absence of evidence is not evidence of absence

There are a few additional studies that have shown no marked rise in OA concentrations in honey post treatment. One of the problems with these studies is that the delay between treatment and honey testing is not clear and is often not stated 13.

Consider what the minimum potential delay between treatment and honey harvesting would be if it were allowed or recommended.

One day 14.

No one has (yet) tested OA concentrations in honey immediately following treatment, or the (presumable) decline in OA levels in the days, weeks and months after treatment. Is it linear over time? Does it flatline and then drop precipitously or does it drop precipitously and then remain at a very low (background) level?

Oxalic acid levels over time post treatment … it’s anyones guess

How does temperature influence this? What about colony strength and activity?

Frankly, without this information we’re just guessing.

Why risk it?

I try and produce the very best quality honey possible for friends, family and customers.

The last thing I would want to risk is inadvertently producing OA-contaminated honey.

Do I know what this tastes like? 15

No, and I’d prefer not to find out.

Formic acid and thymol have been shown to taint honey and my contention is that thorough studies to properly test this have yet to be conducted for oxalic acid.

Until they are – and unless they are statistically compelling – I will not treat colonies with supers present … and I think those that recommend you do are unwise.

What are the options?

Other than MAQS there are no treatments suitable for use when the honey supers are on. If there’s a good nectar flow and a mite-infested colony you have to make a judgement call.

Will the colony be seriously damaged if you delay treatment further?

Quite possibly.

Which is more valuable 16, the honey or the bees?

One option is to treat, hopefully save the colony and feed the honey back to the bees for winter (nothing wrong with this approach … make sure you label the supers clearly!).

Another approach might be to clear then remove the supers to another colony, then treat the original one.

However, if you choose to delay treatment consider the other colonies in your own or neighbouring apiaries. They are at risk as well.

Finally, prevention is better than cure. Timely application of an effective treatment in late summer and midwinter should be sufficient, particularly if all colonies in a geographic area are coordinately treated to minimise the impact of robbing and drifting.

I’ve got two more articles planned on midseason mite management for when the colony is broodless, or can be engineered to be broodless 17.


A tale of two swarms

Or … why it’s good practice to clip the wing of the queen.

After a cool start to May it’s now (s)warmed up nicely. Colonies are piling in nectar, mainly from the OSR, and building up really strongly.

It’s at times like these that vigilance is needed. A skipped inspection, a missed queen cell, and the season can go from boom to bust as 75% of your workforce departs in a swarm.

Not the entire season … but certainly the first half of it.

All beekeepers lose swarms … but should try not to

Natural comb

Natural comb …

All beekeepers lose swarms.

At least, all honest ones do 😉

However, I can think of at least four reasons why it’s pretty shoddy beekeeping practice to repeatedly lose swarms 1.

  1. Beekeepers like bees, but some of the general public do not. Some are frightened of bees and a few risk a severe (or even fatal) anaphylactic reaction if stung. Beekeepers have a responsibility not to frighten or possibly endanger non-beekeepers.
  2. Most swarms do not survive. Studies of ‘wild’ bees have shown that swarming is an inherently risky business 2. The swarm needs to find a suitable new home and then collect sufficient nectar to draw enough comb to build up the colony and store food for the  winter. The vagaries of the weather, forage availability and disease ensure that most swarms do not overwinter successfully.
  3. Swarms have a high Varroa load. The mites transfer a heady mix of unpleasant viruses within the colony, shortening the lives of the overwintering bees. With high virus and mite loads the swarm colony is likely to be robbed by nearby strong colonies. This effectively transfers the mites and viruses to nearby managed colonies, so risking their survival.
  4. The swarmed colony is left with a new virgin queen. She has to mate successfully to ensure the continued survival of the colony. Again, the vagaries of the weather mean that this isn’t certain.

And you get less honey 🙁

Regular inspections help prevent the loss of swarms. But it’s good to get all the help you can.

Here’s a brief account of two recent events that illustrate the differences between swarms from colonies with clipped queens or unclipped queens.

Swarm in an out apiary

I have an out apiary in a reasonably remote spot containing half a dozen colonies. I keep my poorly behaved bees there 🙂 There are other apiaries in the area as the forage is good.

I went to inspect the hives at the end of April. This was only the second inspection of the year. On arriving I found most colonies were very active, but one was suspiciously quiet.

Thirty metres away there was a swirling mass of bees settling in the low branches of a conifer.

My three initial thoughts were “Aren’t swarms a great sight?”“Dammit, they shouldn’t have swarmed!” and “Perfect timing, where’s the skep?”.

Skep and swarm

Skep and swarm

The skep was in the car. It usually lives there during the swarming season. The bees were spread over two or three branches, all drooping under the weight. After a bit of gardening I managed to drop the majority of the bees into the upturned skep 3.

I inverted the skep over a white sheet laid out on the grass and propped one side up using a bit of wood.

The air was full of bees. While I busied myself inspecting the lively (in more ways than one 😉 ) colonies, the swarm gradually started to settle into the skep.

Skep and swarm

Skep and swarm

There were lots of bees exposing the Nasonov’s gland at the end of the abdomen, fanning frantically at the entrance to the upturned skep. This is a pretty certain indication that I’d managed to get the queen into the skep.

Fanning bees

Fanning bees

An hour later I’d finished all but one inspection – the quiet colony – it was beginning to get cool and the light was fading.

I could no longer see eggs, not because there weren’t any but because I’m not an owl.

The swarm still needed to be hived so I left the quiet colony until the following day, wrapped the skep in the sheet and took it to another apiary.


And then the temperature plummeted. For the following week the daytime highs barely reached double figures. Nighttime temperatures were low single digit Centigrade.

The swarm would likely have perished and had a virgin queen emerged in the ‘quiet hive’ she’d have not got out to mate.

I didn’t look in another hive until the 7th, but when I did I got a surprise.

The ‘quiet hive’ contained a marked laying queen. I’d requeened this colony late in 2018 and my notes were a little, er, shambolic 🙁

I’d not recorded whether the queen was clipped and marked (the usual situation), marked only (not entirely unusual) or clipped only (not unknown!).

Whatever, they hadn’t swarmed after all 🙂

They were quiet because they had a high Varroa load with overt signs of DWV infection. Mite and virus levels in late September had been checked and confirmed to be very low. Presumably the mites had been acquired by drifting or robbing late in the season 4.

The hived swarm contained an unmarked laying queen and are lovely calm bees 🙂

A swarm in my home apiary

Fewer photos for this one as I didn’t have a camera with me …

I arrange my hives with the frames oriented ‘warm way’ 5 and inspect them standing behind the hive to avoid returning foragers.

Number 29, your time is up.

Number 29, your time is up.

Earlier this week I noticed a few bees flying under the DIY open mesh floor (OMF) from behind one hive. It’s not unusual to have bees at knee height during inspections but since all I was doing was dropping a nuc off in the apiary I didn’t give it much more thought.

Later in the week I returned to do the weekly inspection.

There were more bees going underneath the hive.

With a bit of effort I peered under the floor to find a 5cm deep slab of bees almost entirely filling the space under the OMF.

Better notes means you know what to expect

My notes were much more comprehensive this time 😉

I knew that the colony had a 2018 white marked and clipped queen.

I removed the supers (which were reassuringly heavy) and quickly inspected the brood box.

Lots of bees, lots of sealed brood, some late-stage larvae but no eggs.

In addition I could see two queen cells … one sealed and one about 3-4 days old, unsealed and with a fat larva sitting in a thick bed of Royal Jelly.

Don’t panic

It was pretty obvious what had happened.

The colony had swarmed 6 but the clipped queen, being unable to fly, had crashed to the ground in a very unregal manner, climbed back up the hive stand and sheltered under the OMF. The swarm had then clustered around her.

They had probably been there for a few days.

Another swarm hived

I placed a new floor and brood box next to the swarmed colony, with the entrance facing the ‘back’. I removed the swarmed brood box and, with a sharp shake, dumped the entire slab of swarmed bees from underneath the OMF into the new hive.

Before adding back all the brood frames I peered into the box as a tsunami of bees started moving from the floor up the side walls.

There! A white marked clipped queen 🙂

White clipped and marked queen returning to the colony

You’ll now have a better chance of finding and keeping her if they swarm.

It’s always reassuring to know where the queen is … and to have good enough notes to know what to look for 😉

I assembled and closed up the new hive and put the swarmed hive back in its place. I then carefully went through every frame checking for queen cells again.

There were only two. I destroyed the sealed cell. I didn’t know how old it was and couldn’t be certain it contained a developing queen.

In contrast, I could ‘age’ the unsealed cell (3-4 days) and knew it contained a larva and copious amounts of food.

I prefer to know when a queen emerges rather than save a few days by leaving the sealed cell. I only generally leave one cell to prevent casts being lost.

There were very young larvae in the colony. It is therefore possible the bees could generate more queen cells in the next day or so. Since I know when the queen will emerge I can check the colony before then and destroy any further cells they generate.

Two swarms, the same outcome … lessons learned

As far as this beekeeper (and I hope the bees 7) is concerned both swarms had a satisfactory outcome.

A number of lessons can be learned from events like these:

  • All beekeepers ‘lose’ swarms. Weather, work, emergencies and life generally can conspire to interrupt the 7 day inspection cycle. Sod’s Law dictates that when it does, the colony will swarm. I’m reasonably conscientious about inspections but I completely missed the signs the home apiary colony was about to swarm.
  • The weather can change suddenly. The swarm in the conifer would have probably perished from the cold in early May. If the weather had stayed warm the scout bees would have found a welcoming church tower or roof space to occupy in a day or so. In both cases the swarm would have been truly lost.
  • It’s always good to carry equipment to capture a swarm. A sheet and a skep, or a large nuc box. Secateurs make ‘gardening’ easier (mine are no longer AWOL). Spare equipment (hives) is essential during the swarm season.
  • An obviously smaller-than-expected colony and a nearby swarm may well be completely unrelated. Check why the colony is weak and take remedial action if needed (mine has Apivar strips in now).
  • Colonies near my out apiary appear to have high mite levels. Since that’s where the conifer swarm came from this also now has Apivar strips in.
  • When is a lost swarm not lost? When the queen is clipped. The queen cannot go far so neither can the swarm. If she returns to the hive stand or the underside of the floor, so will the swarm. If she perishes for some reason the swarm usually returns to the original hive.
  • You can keep bees without knowing where the queen is, but it’s easier if you do. Marking her helps find her, clipping her wing helps keep her there 8.
  • Similarly, knowing when the queen will emerge allows you to predict when she will be mated and start laying. You can avoid interrupting her returning from her mating flight and – before then – you can remove other queen cells to prevent the loss of a cast from a strong colony.
  • Good notes help. Keep them 😉

It’s relatively easy to find unmarked queens in smallish colonies early in the season. It’s a lot harder to find them in a strong colony in mid-May.

Mid-May ... 45,000 bees, 17 frames of brood, one queen ... now marked

Mid-May … 45,000 bees, 17 frames of brood, one queen … now marked and clipped

But it’s worth finding her, marking her and clipping one wing.

If you don’t the swarm you lose might really be lost 😉






Another apiculture-flavoured tale of daylight robbery, literally, to follow the post on hive and bee thefts last week.

However, this time it’s not dodgy bee-suited perps with badly inked prison tats offering cheap nucs down the Dog and Duck.

Like other offenders, the robbers this week wear striped apparel, but this time it’s dark brown and tan, or brown and yellow or black and yellow.

I am of course referring to honey bees and wasps (Vespa vulgaris and V. germanica), both of which can cause major problems at this time of year by robbing weak colonies.

Carb loading

The season here – other than for those who have taken colonies to the heather – is drawing to a close. The main nectar sources have more or less dried up in the last fortnight. There’s a bit of rosebay willow herb and bramble in the hedgerows and some himalayan balsam in the river valleys, but that’s about it.

Colonies are strong, or should be. With the dearth of nectar in the fields, the foragers turn their attention to other colonies as a potential source of carbohydrates. Colonies need large amounts of stores to get through the winter and evolution has selected a behavioural strategy – robbing of weaker colonies – to get as much carbohydrate from the easiest possible sources.

Like the nucs you carefully prepared for overwintering 🙁

At the same time, wasps are also wanting to pile in the carbs before winter 1. In the last fortnight the wasp numbers in my apiaries and equipment stores have increased significantly.

Jekyll and Hyde

Within a few days in late summer/early autumn the mood and attitude of colonies in the apiary changes completely.

During a strong nectar flow the bees single-mindedly pile in the stores. They alight, tail-heavy, on the landing board, enter the hive, unload and set out again. There’s a glut and they ignore almost anything other than bingeing on it. Inspections are easy. Most bees are out foraging and they are – or should be – well-tempered and forgiving. 

Laden foragers returning ...

Laden foragers returning …

But then the nectar flow, almost overnight, stops.

Colonies become markedly more defensive. They are packed with bees and they’re tetchy. There’s nothing to distract them, they resent the intrusion and they want to protect their hard-won stores 2.

At the same time, they quickly become more inquisitive, investigating any potential new source of sugar. If you shake the bees off a frame and leave it standing against the leg of the hive stand there will be dozens of foragers – many from nearby colonies – gorging themselves on the nectar.

If you spill unripened nectar from a frame they’re all over it, quickly forming a frenzied mass – probably from several different hives – scrabbling to ‘fill their boots’.

They also closely investigate anything that smells of nectar or honey. Stacks of equipment, empty supers, hive tools, the smoker bellows … anything.


And it’s this behaviour that can quickly turn into robbing.

The foragers investigate a small, dark entrance that smells of honey … like a nuc in the corner of the apiary. They enter unchallenged or after a little argy-bargy 3, find the stores, stuff themselves, go back to their colony and then return mob-handed.

Before long, the nuc entrance had a writhing mass of bees trying to get in, any guards present are soon overwhelmed and, in just a few hours, it’s robbed out and probably doomed.

This is the most obvious – and rather distressing – form of robbing. Wasps can do almost exactly the same thing, with similarly devastating consequences.

Prevention is better than cure

Once started (and obvious), robbing is difficult to stop. About the only option is to seal the target hive and remove it to another apiary a good distance away.

Far better to prevent it happening in the first place.

The best way of preventing robbing is to maintain large, strong and healthy colonies. With ample bees there are ample guards and the colony will be able to defend itself from both bees and wasps. Strong colonies are much more likely to be the robbers than the robbed.

For smaller colonies in a full-sized hive, or nucleus colonies or – and these are the most difficult of all to defend – mini-nucs used for queen mating, it’s imperative to make the hive easy to defend and minimise attracting robbers to the apiary in the first place.

The underfloor entrances on kewl floors are much easier to defend than a standard entrance and small entrances are easier to defend than large ones. ‘Small’ might mean as little as one bee-width … i.e. only traversable by a single bee at a time.

Smaller is better ...

Smaller is better …

You can even combine the two; insert a 9mm thick piece of stripwood into the Kewl floor entrance to reduce the space to be defended to a centimetre or two. If – as happened tonight when returning wet supers to the hives – I don’t have a suitable piece of stripwood in the apiary I use a strip of gaffer tape to reduce the entrance 4.

Gaffer tape is also essential to maintain the integrity of the hive if some of the supers are a bit warped. Wasps can squeeze through smaller holes than bees and the quick application of a half metre along the junction between boxes can save the day 5.

The poly nucs I favour have a ridiculously large entrance which I reduce by 90% using foam blocks, dried grass, gaffer tape, wire mesh or Correx.

Correx, the beekeepers friend ...

Correx, the beekeepers friend …

Don’t tempt them

Finally, reduce the inducement robbers – whether bees or wasps – have to investigate everything in the apiary by not leaving open sources of nectar, not spilling honey or syrup, clearing up brace comb and ensuring any stored equipment is ‘bee proof’.

You don’t need to inspect as frequently at this time of the season. The queen will have reduced her laying rate and colonies are no longer expanding. With no nectar coming in they should have sufficient space in the brood nest. There’s little chance they will swarm.

If you don’t need to inspect, then don’t. The ability to judge this comes with experience.

If you do have to inspect (to find, mark and clip a late-season mated queen for example 6 do not leave the colony open for longer than necessary. Any supers that are temporarily removed should be secured so bees and wasps cannot access them.

Wet supers

If you’re returning wet supers after extraction, do it with the minimum disruption late in the evening. These supers absolutely reek of honey and attract robbers from far and wide. Keep the supers covered – top and bottom – gently lift the crownboard, give them a tiny puff of smoke, place the supers on top, replace the roof and leave them be.

Returning wet supers

Returning wet supers …

In my experience wet supers are the most likely thing to trigger a robbing frenzy. I usually reduce the entrance at the same time I put the wet supers back and try to add wet supers to all the colonies in the apiary on the same evening 7.

I generally don’t inspect colonies until the supers are cleaned out and ready for storage.


Sphere of influence

How far do honey bees fly? An easy enough question, but one that is not straightforward to answer.

The flight range of the honeybee ...

The flight range of the honeybee …

Does the question mean any honey bee i.e. workers, drones or the queen? As individuals, or as a swarm?

Is the question how far can they fly? Or how far do they usually fly?

Why does any of this matter anyway?

Ladies first …


The first definitive experiments were done by John Eckert in the 1930’s. He located apiaries in the Wyoming badlands at increasing distances from natural or artificial forage 1. Essentially the bees were forced to fly over a moonscape of rocks, sand, sagebrush and cacti to reach an irrigated area with good forage. He then recorded weight gain or loss of the hives located at various distances from the forage.

Wyoming badlands

Wyoming badlands …

The original paper can be found online here (PDF). The experiments are thorough, explained well and make entertaining reading. They involved multiple colonies and were conducted in three successive years.

Surprisingly, Eckert showed that bees would forage up to 8.5 miles from the colony. This means they’d be making a round trip of at least 17 miles – and probably significantly more – to collect pollen and nectar.

However, although colonies situated within 2 miles of the nectar source gained weight, those situated more than 5 miles away lost weight during the experiments.

Gain or loss in hive weight ...

Gain or loss in hive weight …

Therefore, bees can forage over surprisingly long distances, but in doing so they use more resources than they gain.

John Eckert was the co-author (with Harry Laidlaw) of one of the classic books on queen rearing 2. His studies were probably the first thorough analysis of the abilities of worker bees to forage over long distances. Much more recently, Beekman and Ratnieks interpreted the waggle dance (PDF) of bees to calculate foraging distances to heather. In these studies, only 10% of the bees foraged ~6 miles from the hive, although over 50% travelled over 3.5 miles.


Queens don’t get to do a lot of flying. They go on one or two matings flights, perhaps preceded by shorter orientation flights, and they might swarm.

Heading for a DCA near you ...

Heading for a DCA near you …

I’ll deal with swarms separately. I’ll also assume that the orientation flights are no greater than those of workers (I don’t think there’s any data on queen orientation flight distance or duration) at no more than ~300 metres 3.

On mating flights the queen flies to a drone congregation area (DCA), mates with multiple drones and returns to the colony. DCA’s justify a complete post of their own, but are geographically-defined features, often used year after year.

There are a number of studies on queen mating range using genetically-distinguishable virgin queens and drones in isolated or semi-isolated locations. They ‘do what they say on the tin’, drone congregate there and wait for a virgin queen

In the 1930’s Klatt conducted studies using colonies on an isolated peninsula and observed successful mating at distances up to 6.3 miles

Studies in the 1950’s by Peer demonstrated that matings could occur between queens and drones originally separated by 10.1 miles 4. These studies showed an inverse relationship between distance and successful mating.

More recently, Jensen et al., produced data that was in agreement with this, with drone and queen colonies separated by 9.3 miles still successfully mating 5.

However, this more recent study also demonstrated that more than 50% of matings occurred within 1.5 miles and 90% occurring within 4.6 miles.

Just because they can, doesn’t mean they do 🙂

Drones … it takes 17 to tango …

Seventeen of course, because that’s one queen and an average of 16 drones 😉

There’s a problem with the queen mating flight distances listed above. Did the queen fly 9 miles and the drone fly just a short distance to the DCA?

Or vice versa?

10 miles ... you must be joking!

10 miles … you must be joking!

Or do they meet in the middle?

Do queens choose 6 to fly shorter distances because it minimises the risk of predation and because they are less muscle-bound and presumably less strong flyers than drones?

Alternatively, perhaps drones have evolved to visit local DCAs to maximise the time they have aloft without exhausting themselves flying miles first?

Or getting eaten.

It turns out that – at least in these long-distance liaisons – it’s the queen that probably flies further. Drones do prefer local DCAs 7 and most DCAs are located less than 3 miles from the ‘drone’ apiary 8.


I’ve discussed the relocation of swarms recently. Perhaps surprisingly (at least in terms of forage competition), swarms prefer to relocate relatively near the originating hive. Metres rather than miles.

The sphere of influence

Effective foraging – in terms of honey production (or, for that matter, brood rearing) – occurs within 2-3 miles of the hive. This distance is also the furthest that drones usually fly to occupy DCAs for mating.

Queens can fly further, but it’s the law of diminishing returns. Literally. The vast majority of matings occur within 5 miles of the hive.

In fact, other than under exceptional circumstances, a radius of 5 miles from a colony probably represents its ‘sphere of influence’ … either things that can influence the colony, or that the colony can influence.

Why does this matter?

Worker flight distances are relevant if you want to know the nectar sources your bees are able to exploit, or the pollination services they can provide. In both cases, closer is better. It used to also be relevant in trying to track down the source of pesticide kills, though fortunately these are very much rarer these days.

Closer is better ...

Closer is better …

Workers not only fly to forage on plants and trees. They also fly to rob other colonies. I don’t think there are any studies on the distances over which robbing can occur, but I’ve followed bees the best part of a mile across fields from my apiary to find the source of the robbing 9.

All of these movements can also transport diseases about, either in the form of phoretic Varroa mites piggybacking and carrying a toxic viral payload, or as spores from the foulbroods.

Drone and queen flight distances are important if you’re interested in establishing isolated mating sites to maintain particular strains of bees. My friends in the Scottish Native Honey Bee Society have recently described their efforts to establish an isolated queen mating site in the Ochil Hills.

And I’m interested as I now have access to a site over 6 miles from the nearest honey bees in an area largely free of Varroa.

It’s not the Wyoming badlands, but it’s very remote 🙂


If Carlsberg did apiaries …

How about this for an apiary in a truly stunning location?

If Carlsberg did apiaries ...

If Carlsberg did apiaries …

I discovered this apiary while out walking in the Andalucian hills in Southern Spain in mid-May. It was at the end of a forest track, miles from anywhere, with breathtaking views over the cork oak woods South towards the Strait of Gibraltar. It was a bit hazy that afternoon, but on a good day you can clearly see across the Strait to the Rif mountains in Morocco (~100 miles distant), with the faintest trace of the Middle Atlas beyond them.

Not just a pretty view

The photo doesn’t really do justice to the location of the apiary. Yes, the view was great, but what was at least as impressive was the amount of wildflowers around. It’s not an arable area. Most of the farmland was olive trees or lemons, with large areas of wildflower meadow and mixed deciduous woodland. Much of this was cork oak, but it was interspersed with Corsican pines and a variety of other things I couldn’t name.

Wildflower meadow Andalucia

Wildflower meadow Andalucia

I’d be surprised if any of it ever sees a spray of any kind, and the only grazing is by horses, a few feral goats and the elusive wild boar 1. The scene on the right is typical and the road verges were the same, with acres and acres of these beautiful “weeds” everywhere.

Unsurprisingly, the other thing missing from these pictures is the noise.

Everywhere I walked – even on days when I barely left the fringes of the village – I was accompanied by the incessant drone of insects. There were bees everywhere and – again unsurprisingly – the local mixed floral honey was fantastic.

From a beekeeping point of view it really did seem idyllic. Perhaps the only issue would be the temperature. In Spring the midday temperatures were in the mid-20’s (°C) and – going by my experience of working colonies in the bee shed – that can get pretty hot and tiring in a bee suit.


There were about 20 hives in the apiary, lined up on pallets all in full sun. Unlike other apiaries in the area there was no registration number displayed, so it might have been a temporary site from which the hives would be moved in high summer.

Andalucian apiary

Andalucian apiary

To a beekeeper familiar with the stackable boxes of a National or Langstroth, the hives were unusual. The majority were single boxes, with hinged lids and one or two entrances low down at the front.

Layens hive

Layens hive

These are Layens hives, a single large, deep box containing 15 or more frames. Each frame is about the same width as a British National brood frame, but is almost twice as deep. Georges de Layens, who invented the hive in the 19th Century, designed it for minimal management beekeeping.

No weekly inspections, no overt swarm control, simply give the bees sufficient room in a well-insulated hive and return to harvest the honey at the end of the season.

Can it really be that simple?

Well, it certainly could be that simple.

However, Layens developed the hive long before Varroa appeared on the scene, and monitoring and managing disease in a hive with no removable or open mesh floor – particularly with only a couple of inspections a season – seems an unlikely recipe for success to me 2.

It’s reported that there are still more than a million Layens hives in use in Spain and the hive design has some strong supporters in the US 3. The hive design also lends itself to migratory beekeeping as there are no teetering stacks to be strapped together for transport.

Spanish readers of this site represent less than 0.5% of the annual visitors … if you are one of them please add a comment on the practicalities of beekeeping using the Layens hive.

But it’s not all sunshine and roses

Derelict Spanish apiary

Derelict Spanish apiary

I’ve visited this area of Andalucia for several years. Near the village is an apiary that has – year by year – slowly been falling into disrepair. There were originally ~20 hives in lightly shaded woodland surrounded by wildflower meadows. It was a lovely spot, just off a little-used track, protected from the midday sun, secure yet accessible … though the view wasn’t a patch on the one at the top of the page.

Five years ago most hives – all Layens again – were busy with bees and I remember being surprised by the number of hornets hawking around. The apiary carried a registration number and the hives were scruffy, but functional.

Year by year the number of hives on their side, open, damaged or otherwise clearly defunct has gradually increased. Corners of the apiary filled with broken and discarded frames or other rubbish.

By this Spring it was all over. There were still about 20 hives in the apiary, but none of them were upright and functional. The few that were upright were non-functional and the only one containing bees was badly damaged and on its side, with the bees gaining access from a split in the corner.

It appeared as though the apiary had been abandoned by just about everything other than the Jabalí … and they’d had a field day ransacking the hives.

Ransacked Layens hive ...

Ransacked Layens hive …

Abandoned hives, robbing and mites

Of course, I don’t know the back story … an ageing beekeeper unable to cope any longer, hives inherited by someone without sufficient interest or beekeeping skills, or simply an unproductive apiary that was forgotten.

Bees entering an abandoned Layens hive

Bees entering an abandoned Layens hive

The hives were largely stripped out, but at one point must have posed a disease risk for neighbouring colonies. Unless mite levels were controlled the colonies would eventually succumb to Varroa-transmitted viruses. As the colony weakens it is likely to get robbed-out by strong colonies from nearby apiaries.

The robbers returning to their colonies carry honey and hitchhiking phoretic mites. This is what the Americans call a “mite bomb”.

There’s good evidence that this route of mite transmission peaks late in the season during a dearth of nectar. This is one of the reasons that justifies coordinated mite treatments at the correct time of the year to protect the winter bees.


I have no imagination … I’ve used the “If Carlsberg did …” prefix a couple of times already, when discussing smokers and vaporisers. I’ll try and think of something a little more original for the future. In my defence I have spent 50% of the last four weeks abroad, successfully controlled swarming (by vertical splits or Pagdens’) in over half of the ~25 colonies I’m currently managing, run out of supers, brood boxes and frames (D’oh!) and been involved in some exciting new plans for going Varroa-free in the future. Watch this space.

Keep your distance

A recent paper by Nolan and Delaplane (Apidologie 10.1007/s13592-016-0443-9) provides further evidence that drifting/robbing between colonies is an important contributor to Varroa transmission. In the study they established multiple pairs of essentially Varroa-free colonies 0, 10 or 100 metres apart and then spiked one of the pair with a known number of Varroa. They then monitored mite build-up in the paired colonies over several months. By comparison of the relative mite increases in colonies separated by different distances they showed that the more closely spaced, the more likely they were to acquire more Varroa, presumably through robbing or drifting.

This isn’t rocket science. However, it’s a nicely-conducted study and emphasises the importance of colony spacing on the transmission of phoretic mites between infested and uninfested colonies – through the normal colony activities such as robbing and drifting – as a primary cause of deformed wing virus (DWV) disease spread in the honey bee population. The paper only studies mite levels, but the association with DWV transmission is well established and unequivocal.

Related studies on the influence of colony/apiary separation

The introduction to the paper provides a good overview of the prior literature on the impact of drifting on disease and Varroa transmission, some of which has already been discussed here. However, some of these studies have not previously been mentioned and deserve an airing, for example:

  • Sakofski et al., (1990) showed that there was no difference in mite migration between colonies in closely-spaced rows from those located up to 10m apart.
  • Frey and Rosenkranz (2014) showed that high-density colonies (>300 within flight range [2.5 km] of the sentinel colonies) experienced approaching 4-fold greater inbound mite migration than when located in areas containing a low-density of treated colonies. Over a 3.5 month period the difference was 462 +/- 74 vs. 126 +/- 16 mites. This would have a very significant impact if allowed to subsequently replicate in the recipient colonies.
  • Frey et al., (2011) previously investigated mite transfer between colonies located 1m to 1500m apart. Strikingly, in this study (which was conducted during a dearth of nectar) mite transmission was effectively distance-independent, with the recipient colonies acquiring 85 – 444 mites over a 2 month period.
Frey and Rosenkranz (2014) Mite invasion ...

Frey and Rosenkranz (2014) Mite invasion …

What can we conclude from these studies?

  1. Closely-spaced colonies – for example, the sort of distances used to separate colonies in an apiary – should really be viewed as a single location as far as mite infestation is concerned. A single heavily-infested colony in an apiary will quickly act as a source of mites to all other colonies.
  2. High densities of beekeepers – assuming the usual range in both the timing and vigour with which Varroa control is practised – is probably detrimental to maintaining low mite levels in your own bees.
  3. Significant mite transmission occurs over distances of at least 1.5 km … not just between hives in a single apiary. How many colonies are there within 1.5 km of your own apiary? Even if you are careful about controlling mite levels, what about all the beekeepers around you?
  4. Colonies wth uncontrolled levels of mite infestation, abandoned colonies (or swarms that occupy abandoned hives) and feral colonies located at least 1.5 km away are potential sources from which your carefully-maintained hives get re-infested …

Recent experience with high and low density beekeeping

One mile radius ...

One mile radius …

I’ve moved in the last year from the Midlands to Fife. Beebase and my involvement with local beekeepers suggest that these represent areas of high and low colony-density respectively. For comparison, Beebase indicates that there were over 230 apiaries within 10 km of my home apiary in the Midlands and that there are currently 20 within a similar range in Fife. In the Midlands I was aware of at least 25 colonies (in several different apiaries) within a mile of one of my apiaries. Furthermore, apiaries might contain lots of hives … one of those previously within 10 km of my home apiary was our association apiary which held up to 30 colonies from ~15 beekeepers. In contrast, the closest beekeeper to my current home apiary is almost 3km away … though I acknowledge there may well be hives “under the radar” belonging to beekeepers that are not members of the local association or have not bothered to registered on Beebase (why not?). It’s far too early to be definitive but mite levels in my colonies have been reassuringly low this season. This includes uncapping hundreds of drone pupae – the preferred site for Varroa to replicate – without detecting a single mite. I’d like to think this was due to timely and effective Varroa control, but it is undoubtedly helped because my neighbours are further away … and perhaps better at controlling the mite levels in their own colonies.

This study provides further compelling evidence of the importance of either keeping colonies isolated (which may not be possible) and ensuring that all colonies in the same and adjacent apiaries are coordinately treated during efforts to control mite numbers.

Gaffer tape apiary

Gaffer tape apiary …

The Drifters cont.

The Drifters ...

The Drifters …

Not the legendary American doo-wap/R&B vocal group but instead a quick follow-up to a recent post on drifting in honey bees. I discovered an interesting article in a 2011 issue of American Bee Journal in which Wyatt Mangum (Mangum, W. [2011] Varroa immigration and resistant mites ABJ 151:475) quantified mites introduced with bees from other colonies. The experiment was straightforward and quite clever … a number of colonies were prepared with very low mite numbers, overwintered and then miticides (unspecified, but from the remainder of the article I’m assuming Apistan) were applied continuously for the rest of the season. This would kill all the mites present. With a Varroa tray in place it was therefore possible to count newly introduced mites throughout the season. These must arrive with drifting workers, drones (not sure if drones ‘drift’ as such … perhaps there’s a better term for their itinerant wandering?), bees that have abandoned other colonies or potentially robbers. The newly infesting mites would of course be killed by the miticide after introduction and before reproduction. They could therefore easily be counted on the Varroa tray under the open mesh floor.

The results were striking … in one year between mid-May and early October an average of 1415 and 1001 mites were introduced to each of the seven ‘recipient’ colonies in two separate apiaries. Mite arrivals weren’t evenly spread, but peaked during a late summer dearth of nectar … perhaps, as suggested by the author, as other colonies started to run out of stores. The source colonies were not identified, but were not within the test apiaries. Whatever the cause, this represents a very significant influx of up to 7-10 mites per day. In Mangum’s experiment these mites could not replicate (due to the miticide that was always present). Had they been able to do so the impact on the recipient colony, in terms of numbers of mites transmitting viruses within the hive, would have been much greater.

The impact of drifting and mite reinfestation

The impact of drifting and mite reinfestation

Using BEEHAVE this impact can be modelled. In untreated colonies (solid lines), primed with 20 mites at the beginning of the year (and default conditions as previously described), the average mite level at the year end is ~430 (n=3) having reached a maximum of ~600. Using the same infestation period as reported by Mangum¹, with a mite infestation rate of 7/day (the lowest he observed), the average mite levels at the year end were ~2700 (n=3), with maximum levels reaching ~3800 in late summer (dotted lines). In this simulation the introduced mites can reproduce. Therefore, within just a few months, phoretic mites carried on workers and drones from other colonies, have the potential to raise mite levels in the recipient colony to dangerously high levels – significantly higher than the maximum recommended level of 1000/colony. This is potentially of fundamental importance in strategies to effectively control Varroa.  It should be noted that in a repeat of his study this large scale infestation was not observed. This suggests that this type of infestation – from outwith the apiary – may only be a problem in certain years or under specific conditions. One possibility that comes immediately to mind would be a collapsing feral colony or abandoned (or potentially not abandoned, but just completely ignored and untreated … or ‘abandoned‘ as some might say 😉 ) hive within foraging distance.

Ample opportunity ...

Ample opportunity …

Interestingly, a recent study has looked at the influence of a number of honey bee pathogens on drifting (or inter-colonial transmission as they rather long-windedly call it) behaviour. Of the viruses, Varroa and Nosema tested, only the presence of high mite levels influenced drifting … but not in the direction that might be expected. Distance between colonies in an apiary was the major factor that influenced drifting and ~17% of tested workers had drifted (with a third to half of these being apparently unrelated to other colonies in the test apiary). Surprisingly, colonies with high Varroa levels were more likely to acquire drifting workers, though the mechanism for this was unclear. The increased mixing through drifting would ensure that these colonies would likely end up with a greater diversity of viral and other pathogens though whether these colonies could, later in the season, act as a source rather than a sink for mites was not tested.


Drone …

Finally, returning to the subject of drifting bees and the ABJ … in the February 2016 issue there’s an interview with Tom Seeley (of Honeybee democracy fame … Sharashkin, L [2016], ABJ 156:157) in which he states that, when quantified, 34% of drones in his apiary colonies were from other hives. This article – on Surviving without Treatments: Lessons from Wild Bees – also discusses the importance of colony separation to coping with Varroa. The feral colonies Seeley studies are located at least half a mile apart in woodland. When recovered and relocated together in apiaries (‘beeyards’ as they’re called in the US) they rapidly succumb to mite-transmitted viral diseases, whereas those maintained some distance apart (30+ metres) survive. Seeley makes the point that pathogens evolving in closely-spaced colonies are likely to be more virulent, whereas those that are in distantly spaced colonies should be less virulent (or they’ll kill the host colony before being transmitted). Seeley is referring to the virulence of Varroa but I think his comments apply better to the viral payload carried by the mite. This is a relatively minor distinction but these observations further emphasise that drifting in honey bees is clearly a major factor in mite, and consequently disease, transmission … and therefore needs to be considered in control.

STOP PRESS – A recent Bee-L post highlighted a further study on the influence of re-infestation. Greatti et al., (1992) showed that ~2-14 mites/day/colony were acquired in their test apiary during June-August, and that this number rose to up to 75 mites/day/colony in September and October². This type of re-infestation can occur by drifting as already discussed, or by workers in the sentinel colonies robbing out mite-infested collapsing nearby hives or feral colonies.

¹In the Mangum study the mites did not infest the sentinel colonies at an even rate of 7+/day. Instead there was a marked peak in mid-season. I’ve not attempted to model this. Clearly if mites don’t arrive earlier in the season the overall levels would be lower (as they wouldn’t have the chance to reproduce). However, an influx of mites in mid/late-season might just arrive at the wrong time to damage the all-important winter bees … the topic of a future post.

²Greatti, M., Milani, N. and Nazzi, F., (1992). Reinfestation of an acaricide-treated apiary by Varroa jacobsoni Oud. Exp. Appl. Acarol., 16: 279-286

Drifting in honeybees

During previous research on deformed wing virus (DWV) biology and its transmission by Varroa I’ve moved known Varroa-free colonies (sourced from a region of the UK which the mite has yet to reach and maintained totally mite-free) into apiaries in the countryside. Within 2-3 weeks Varroa was detectable in sealed brood, showing that mite infestation occurs very readily. I know other researchers who have made very similar observations. Where do these mites come from?

They’re not all ‘your’ bees

The obvious source would be the phoretic mites transported on workers ‘drifting’ from nearby infested colonies, or on drones which are known to travel quite long distances and may be accepted by almost any colony. If you want to see how frequent this is try marking a few dozen drones with a dab of paint. To avoid confusion use the colour used to mark queens next year. There are unlikely to be 4+ year old queens in the apiary and the drones will all perish before the end of the current season. Over the next few days and weeks the drones will appear in adjacent colonies, and some will likely leave the apiary and be accepted in your neighbours colonies.

How to encourage drifting ...

How to encourage drifting …

Beekeepers are usually aware that colonies at the ends of rows often ‘accumulate’ bees that have drifted when returning to the hive. In shared association apiaries some crafty beekeepers will site their colonies at the ends of rows to take advantage of the ‘generosity’ of other colonies. However, many beekeepers probably do not appreciate the extent to which drifting occurs. Pfeiffer and Crailsheim (1998) report that 13-42% of the population of a colony are ‘alien’ i.e. have drifted from adjacent hives, depending upon the time of season. Remember that drifting occurs in both directions simultaneously, so the overall numbers of bees in a colony may not be adversely affected (or boosted). In other studies Sekulja and colleagues (2014) showed that ~1% of marked bees drifted between colonies over a three day observation window. Interestingly, American foulbrood (AFB) infected bees drifted slightly more than uninfected bees. Spread of foulbroods during drifting is one reason the bee inspectors check nearby apiaries when there is an outbreak. These studies were all on workers where drifting primarily occurs during orientation flights before the bees become foragers. Drones drift two to three times more than workers (Free, 1958).

The likelihood of drifting must be closely related to the separation of hives and apiaries. Although workers will forage up to 2-3 miles from the hive I suspect the proportion of bees that drift this distance is extremely small. However, unless you’re very isolated I expect there are other apiaries within a mile or so of your own. Drones are known to fly up to about five miles to reach drone congregation areas for queen mating and are accepted by all colonies. I’ve regularly found drones appearing in (relatively) isolated mini-nucs. I’m not aware of studies that have formally tested drifting between apiaries (though it is reported in passing in the Sekulja et al., 2014 paper cited above).

Consequences of drifting

So, your hives probably contain workers and drones from other nearby colonies, and you can only really be sure that they’re all “your” bees if you live – as the sole beekeeper – on an isolated island. Not only does your neighbour generously exchange bees with you, he or she also kindly shares the phoretic mites those bees are carrying, the viral payload the bees and mites are infected with and – if you’re really unlucky – the Paenibacillus larvae spores responsible for causing AFB infection (and vice versa of course).

There are lessons here that should inform the way we conduct our integrated pest management to maintain healthy colonies. 

This post provides background information for an article (“Viruses and Varroa: Using our current controls more effectively” by David Evans, Fiona Highet and Alan Bowman) in the December 2015 issue of Scottish Beekeeper, the monthly magazine for members of the Scottish Beekeepers Association.

More later …