Synopsis : With so many swarms lost by beekeepers, why are there relatively few feral colonies? Do they die from starvation, depredation or disease? What kills feral colonies?
Introduction
It can take a long time to understand complex natural phenomena. When you take into account geographic and seasonal variation you often end up with an explanation littered with more caveats than actual answers.
For example … do honey bees compete to the detriment of native solitary bees?
During May in an environment with limitless yellow acres of oil seed rape … probably not, but during early spring in an arable area with limited hedgerows … almost certainly.
OSR and threatening clouds
Sometimes the explanation may seem obvious, but isn’t. Bumble bees restrict themselves to field margins whereas honey bees venture hundred of metres into the middle of a field of OSR. Not only are there huge amounts of pollen and nectar available, but the different species exploit it in different areas of the field.
By many accounts, it’s been a very ‘swarmy’ season. The BBKA’s swarm line was swamped 2. Many beekeepers ran out of equipment (and no doubt patience) hiving swarms lost by beelosers with poor swarm control.
With ~250,000 colonies in the UK I wouldn’t be surprised if there were 50-100,000 lost swarms and casts.
That being the case, why aren’t there more feral honey bees?
Synopsis : Swarmtastic! The first swarms of the season and a timely lesson on why swarm control is important and how clipping the queen really helps.
Introduction
Temperatures have finally achieved a ‘typical’ mid-May average of low teens (°C), and on most days the bees are out foraging well. If anything this is making the discrepancy between the strongest hives and the also-rans even more marked. I’ve just put my fourth supers on some, whereas a few hives are struggling to do anything much with the first one.
The oil seed rape in Fife is going over in a few fields, but most still has 10-14 days to go 1 … and the forecast is fantastic, so I’m hoping to still have time to snatch beekeeping victory (or what masquerades as victory for a beekeeper which is full buckets of honey) from the jaws of defeat.
It’s not going to be a bumper spring crop, but it might just about manage average.
Of course, the combination of a good nectar flow and overcrowded colonies means that the bees are now busying themselves with swarm preparations. The post today is all about swarms, lost and found, the benefits of clipped queens and the importance of observation.
Or, to put it another way, more tales of slapstick beekeeping 😉 .
Synopsis : How far do swarms move? Can estimates of environmental apiary and hive densities help determine whether “isolated, lost or ancient” bees are anything of the sort?
Introduction
A little more on feral colonies this week. It’s an interesting topic to think about as the temperature drops, the wind picks up and the trees change into their autumn finery.
A riot of autumn colour
If there are any colonies in the local woods, how did they get there and what are their chances of survival?
I discussed some answers to this last week, using the specific example of old-growth forests in Germany (Kohl et al., 2022). In those cases the reality was that the majority of colonies perished within a year – the average time they survived was only ~32 weeks.
The most likely explanation for their presence in the forest was ‘spillover’ of lost swarms from managed colonies in neighbouring farmland. My assumption – though this wasn’t covered in the paper – was that the colonies perished from either disease or starvation.
This week I want to consider the isolation – or otherwise – of ‘remote’ forests and the distance swarms travel from their origin. Inevitably this will involve some back of an envelope calculations and even outright guesstimates1, so I’ll finish on a more familiar topic (to me) by briefly considering the pathogen loads of feral colonies.
Are these feral healthy and thriving, or riddled with disease?
Beekeepers and hives …
There are about 50,000 beekeepers in the UK and they manage about 250,000 hives.
That’s two ’abouts’ in one sentence, so the guesstimates have started already. The National Bee Unit reports there are 272,000 hives in the UK (2021 figures). They call this an ‘experimental statistic’ because ’several assumptions formed part of the calculations’2. This number is up from 247,000 in 2017.
I suspect some of these assumptions include extrapolating from the numbers of beekeepers/apiaries and hives registered on the National Bee Unit’s BeeBase. In 2013 this was 29,000 beekeepers managing 126,000 colonies.
That extrapolation is needed as not all beekeepers are registered on BeeBase 3, in the same way that not all beekeepers belong to a national or local association.
I’m going to ignore our commercial cousins, the bee farmers. There are only about 400 of them and only one or two of them manage more than 1,000 colonies.
The 2013 BeeBase numbers suggest that registered beekeepers manage 126,000/29,000 = 4.3 hives each. My opening sentence to this section would indicate that the average is perhaps about 5 hives. However, if the experimental statistic is correct but beekeeper numbers are still around 50k, then it’s a little over 5.4 hives per beekeeper.
Let’s keep the maths simple … on average, beekeepers manage 5 colonies 😉 .
… and apiaries
Unfortunately, I’m not aware of any publicly available statistics on hive density, but there is at least partial information available on apiary density.
If you are registered on BeeBase, two of the things you record are the apiary location and the number of hives in each apiary. Once an apiary is registered you can determine the ‘Apiary density within 10 km’ 4.
Beebase shows the ‘density’ of apiaries within 10 km
A radius of 10 km from your registered apiary encompasses 314 km2, so it is perhaps not surprising that there can be a large number of other apiaries in the neighbourhood.
When I lived in Warwickshire my two apiaries – separated by ~5 km – had 255 and 267 apiaries within a 10 km radius. This is a busy beekeeping area, with a very active local association (my alma mater, WLBK).
Hives in the corner of a Warwickshire field (almost every field!)
I don’t know how many hives there were in the surrounding environment, but it seemed as though almost every field margin or spinney contained a little row of hives balanced on old pallets.
Convenient assumptions
On the basis that I don’t have any other information, and in the interest of getting on with the article, I’m going to assume that each apiary contains an average of 5 hives. I think this is reasonable, though I’d be interested if anyone has any real figures.
With ~260 apiaries within 10 km, each containing an average of 5 hives, it suggests the hive density was 4.1 km2.
Coincidentally 5 this is almost exactly the same figure quoted in Kohl et al., (2022) last week.
And each year a significant proportion of these hives will attempt to swarm.
Swarms
With exemplary swarm control it is possible to avoid losing any swarms.
Of course, we do our beekeeping in the real world, and the reality is that we all lose swarms sometimes.
Hopefully not many and perhaps not even every year, but swarms are lost.
When I lived in Warwickshire I never failed to attract swarms to my bait hives each season. When I lived in Fife – where there were only ~45 apiaries within 10 km 6 – I caught four swarms in a bait hive in my back garden one season, and (again) never failed to attract swarms in the time I lived there.
Although I’d like to think this reflects the care I take in preparing my bait hives, I suspect it really means that – during the swarming season – a lot of queen cells are missed and swarms are lost.
Bivouacs and scout bees
Generally, though there are exceptions, the swarming process goes something like this:
the colony starts producing queen cells
on the first good day (warm, dry, fine etc.) after the first queen cells are sealed the colony swarms
the swarm bivouacs nearby, perhaps only 10-20 metres away
scout bees survey the environment for likely new nest sites, ‘dancing’ on the surface of the bivouac to persuade other scout bees to check out promising looking locations
a quorum decision is reached by the scout bees on the ‘best’ new nest site and they lead the swarm there 7
The scout bees survey at least a 2-3 km radius around the original hive; they probably start this process before the colony swarms, continuing it once the swarm has bivouacked. Since we can interpret the waggle dance, it is possible to observe the scout bees and infer from them the approximate distance and direction to the selected nest site.
By doing this, scientists have determined how far swarms usually travel (a relatively short distance) and how far they sometimes go (a long way).
Swarming distances
Most swarms relocate just a few hundred metres from their origin. Martin Lindauer did some of the first studies on swarming distances in the mid-50’s and Thomas Seeley and Roger Morse produced strikingly similar data in 1977 (Seeley and Morse, 1977).
Most swarms only travel a short distance to a new nest site
There are a number of related studies from the early 1980’s which demonstrate that, although scout bees may survey the environment from ~300 m to over 4 km away, at least 50% of swarms move no more than 1 km from their origin.
However, they can travel much further.
In recent studies José Villa studied swarming of bees in Louisiana (Villa, 2004). He studied swarm size (weight), nest volume preference and the timing of swarming. In addition, by interpreting scout bee waggle dancing, he recorded the distance 16 swarms travelled from their origin.
In this study a marked preference for relatively ‘local’ nest sites was not seen. Four swarms travelled less than 1 km, six from 1 to 4 km, five between 4 and 7 km and one ~10 km.
With three of the swarms, two that moved <500 m from the origin and one 2.2 km away, he confirmed their location by finding the uniquely tagged queen present in the original swarm.
Although I said ’they can travel much further’ it’s worth remembering that the distance travelled was inferred from the duration of the waggle run by scout bees on the surface of the bivouacked swarm (and specifically, the predominant dances being conducted 30 minutes before the swarm left the bivouac).
That’s not quite the same as proving that swarms may travel 5-10 km, but it is certainly suggestive that they do.
Isolated woodland in a bee-filled environment
Let’s do a bit more arm waving …
Assume there’s two to three thousand hectares of old native woodland, oak, beech, sycamore etc., rather than conifers. In the absence of black woodpeckers (see last week) some of these trees will still contain hollow cavities. They will have lost boughs or been hit by lightning, the rain will have rotted the exposed heartwood and a cavity will eventually form.
Voilà … a potential nest site for bees 🙂
A wood of 2500 hectares (or is that a forest?), if circular, fills a circle of 5.6 km diameter. Of course, it’s very unlikely to be circular, but it makes the maths easier so bear with me.
Assume this wood is in the middle of good quality mixed farmland, with early season oil seed rape, hedgerows filled with hawthorn and blackberry, and ample clover polka-dotted pasture.
In other words, a good environment for honey bees.
So the local beekeepers plonk a few hives in the corners of fields, or along field margins.
Eventually, the density of these hives reaches 4 km2 (as justified above).
Cartoon of woodland (green) and surrounding farmland (blue and red)
In the diagram above the inner (green) circle is the native woodland. The surrounding blue and red rings represent the surrounding farmland, in each case the area covered by an additional 1 km radius respectively from the centre.
The woodland contains no managed colonies and is 24.6 km2. The blue ring (excluding the central wooded area) has an area of 20.7 km2 and so contains – based upon all those assumptions above – 83 managed hives. Likewise, the red ring has an area of 27 km2 and contains 108 hives.
Define ‘isolated’
As shown above, 50% of swarms move no more than a kilometre to a new nest site, but some move further … and a few may move much further.
Any of the managed hives in the blue ring might produce a swarm that could reach the forest boundary. In addition, assuming the blue ring contained few suitable nest sites – and I’ll return to this point shortly – swarms issuing from hives in the red ring might well travel further and reach the forest.
In fact, if you overlay the roundel diagram with the swarm dispersal diagram – at the same scale – from the paper by Villa (2004) you can see that swarms from a very wide area are ‘in range’ of the hollow tree-filled forest.
Woodland (green) and surrounding farmland with – at the same scale – swarming distances from Villa (2004)
The swarm dispersal diagram shows the swarms starting from a central point, so you just need to imagine the arrows are reversed.
In fact, if you assume that swarms can travel up to 7 km (only one swarm studied by Villa may have gone further, but one third travelled 4-7 km) there could be as many as 517 potentially swarming colonies ‘in range’ 8.
Therefore, as far as migrating swarms are concerned, it’s quite possible that none of the forest is ‘isolated’.
Nest sites in farmland and forests
In the Kohl et al., (2022) paper I discussed last week, the majority of the woodpecker holes used by bees were in large beech trees. The average diameter of the trees was 55 cm when measured 1.5 m above ground.
These were substantial trees.
Trees of that size are common in old growth forest … but they’re rare in farmland.
Hedging, if it hasn’t been grubbed up, contains predominantly small trees. Many small copses and spinneys have also disappeared, all to make way for combine harvesters and subsidies.
Lots of forage but not a lot of mature trees
Of course, there are large trees in farmland, they’re just a whole lot less common than they are in old native woodland.
Therefore swarms issuing from managed hives on farmland – assuming they don’t end up in one of my bait hives – are more likely to gravitate to the forest as there will be more nest sites there.
Blenheim bees
I don’t know much about the widely-publicised ‘Blenheim bees’ that I briefly introduced last week.
However, I do know that the Blenheim Estate near Oxford has about 2500 hectares of woodland, and that there are a lot of beekeepers in Oxfordshire.
That 2500 hectares, if circular (which it isn’t) and centred on Blenheim Palace, would span from Combe to Oxford Airport, and completely covers the small market town of Woodstock 9.
This is a popular area for beekeeping. The National Bee Unit’s ‘BeeBase’ informs me that there are ~200 apiaries within 10 km of Blenheim Palace. Combe to the west has ~190 apiaries within 10 km.
If these apiaries have the expected number of hives in (i.e. 4 km2, and I see no compelling reason why not … for example, the countryside is similar to Warwickshire) then there are a very large number of colonies capable of producing swarms that are well within range of the forested area.
But let’s just revisit that figure of ~200 apiaries within 10 km.
How accurate it is?
Certainly some of the apiaries will have been ‘forgotten’ and are now vacant. I bet there’s a lot of redundant data on BeeBase.
Perhaps ~200 apiaries is not a very accurate figure?
I think it is probably inaccurate … but I strongly suspect it’s an underestimate rather than an overestimate of apiary numbers in the area.
Many beekeepers are not registered on BeeBase. Only the National Bee Unit knows 10 the proportion of beekeepers/apiaries/hives missing, but I’d be amazed if it was less than 25% and not at all surprised if it was 40%.
This is probably part of the ’fiddle factor’ used to extrapolate from BeeBase registrations and hive numbers to that ’experimental statistic’ of 272,000 hives in the UK.
Occam’s razor, the law of parsimony, and ‘isolated’ feral/wild bees
Are there self-sustaining populations of honey bees in the UK?
By self-sustaining I mean not dependent upon an annual influx of swarms from nearby managed colonies. These swarms compensate for the very high winter attrition rate seen in the Kohl et al., (2022) study which is likely due to pathogens and starvation (I’m going to deal with pathogens – briefly – next).
Well, are there?
I don’t know.
Based upon registered and predicted apiary and hive numbers, and the known distances swarms migrate, I think the simplest – and therefore most likely – explanation for feral colonies in ‘isolated’ locations are recent (< 1 year) swarms from nearby managed colonies.
Even assuming the National Bee Unit’s predicted 272,000 hives are evenly distributed over the entire UK (242,000 km2) that’s still >1 hive / km2. They’re obviously not evenly distributed; many areas are unsuitable or, at best, borderline for beekeeping.
I’d like to have been able to discuss the area of old growth forests in the UK and how isolated or otherwise it is. Unfortunately, I don’t have the data … or the GIS mapping skills to interrogate it.
Therefore I’ll close instead with something I know a little more about …
Feral colonies, pathogens and genetics
How healthy are feral colonies in the UK?
There aren’t a lot of published studies. Catherine Thompson and colleagues showed that the pathogen load – including Deformed wing virus (DWV), Black queen cell virus (BQCV) and Nosema (both apis and ceranae) – were similar or higher in feral colonies than in managed colonies (Thompson et al., 2014).
Pathogen levels in feral (F) and managed (M) colonies
Levels of DWV in feral colonies were significantly higher than in managed colonies, but they were similar to the levels seen in beekeeper’s hives not treated to control Varroa infestation.
We know – though many are still bitterly reminded every year – that colonies in which mite levels are high and uncontrolled usually perish overwinter.
Catherine Thompson also studied the genetic characteristics of feral colonies and compared them to managed colonies (Thompson, C. PhD. thesis, University of Leeds, 2010). Her results show that the feral colonies she studied were very similar – and effectively indistinguishable – to managed colonies when the overall level of genetic heterozygosity was analysed. This means that these feral colonies are not a distinct genetic race of bees.
That’s not the same as showing they were genetically related to (and so originated from) nearby managed colonies … those experiments still need to be done.
Are these wild bees self-sustaining, unique and ancient?
If a colony or two of bees (or even a hundred) are found in the woods I’d suggest the following tests need to be applied to convincingly demonstrate they are a unique and self-sustaining population.
how isolated are they really? Are there managed colonies within 5-10 km that could act as a source of swarms? Geographic isolation may be due to factors other than distance, for example an island population, or an isolated valley surrounded with mountains.
is the population truly self-sustaining? Do colonies regularly survive for sufficient time to reproduce? To be self-sustaining, annual colony losses must be less than or equal to new colonies established from the same feral bees.
are the bees genetically distinct from managed colonies within 10 km or so? If they are a well-established population you would expect this.
If the population is truly isolated, reproduces sufficiently to replace annual losses and is genetically distinct, then it may well be self-sustaining.
However, if it doesn’t meet any one of these three criteria then I suspect the population is dependent upon ‘spillover’ losses of swarms from neighbouring managed colonies.
Interesting perhaps, but not surprising, not unique and certainly not ancient.
Unsurprisingly, I’m sceptical about many of the claims made for long lost and unique strains of bees living in the woods (or anywhere else for that matter).
A glimmer of hope (?) … the Arnot Forest bees
The Arnot Forest is not dissimilar in size to Blenheim estate (17 km2vs. 24 km2).
However, it is surrounded by lots more old growth forest (100+ years) and so is effectively more isolated. There are some managed colonies in the surrounding forests, but – when tested – they were genetically distinct from the Arnot Forest bees (Seeley et al., 2015). Finally, the colony survival characteristics (~1.5 years) and annual swarming of the Arnot Forest bees indicates that the population is self-sustaining. These Arnot Forest bees have adapted to live with Varroa through behavioural changes – frequent swarming, small colonies etc.
Clearly, self-sustaining populations of feral colonies can exist 11, but this is not the same as claiming that all feral populations are self-sustaining, unique or ancient.
Finally, it’s worth noting that the mechanisms that self-sustaining populations of bees have evolved to become Varroa tolerant (they are unlikely to be resistance) – small, swarmy, colonies – may make them unsuited for either beekeeping or pollination.
References
Kohl, P.L., Rutschmann, B. and Steffan-Dewenter, I. (no date) ‘Population demography of feral honeybee colonies in central European forests’, Royal Society Open Science, 9(8), p. 220565. Available at: https://doi.org/10.1098/rsos.220565.
Seeley, T.D. et al. (2015) ‘A survivor population of wild colonies of European honeybees in the northeastern United States: investigating its genetic structure’, Apidologie, 46(5), pp. 654–666. Available at: https://doi.org/10.1007/s13592-015-0355-0.
Seeley, T.D. (2017) ‘Life-history traits of wild honey bee colonies living in forests around Ithaca, NY, USA’, Apidologie, 48(6), pp. 743–754. Available at: https://doi.org/10.1007/s13592-017-0519-1.
Seeley, T.D. and Morse, R.A. (1977) ‘Dispersal Behavior of Honey Bee Swarms’, Psyche: A Journal of Entomology, 84, pp. 199–209. Available at: https://doi.org/10.1155/1977/37918.
Thompson, C. (2010) The health and status of the feral honeybee (Apis mellifera sp) and Apis mellifera mellifera population of the UK. phd. University of Leeds. Available at: https://etheses.whiterose.ac.uk/5211/ (Accessed: 19 October 2022).
Thompson, C.E. et al. (2014) ‘Parasite Pressures on Feral Honey Bees (Apis mellifera sp.)’, PLOS ONE, 9(8), p. e105164. Available at: https://doi.org/10.1371/journal.pone.0105164.
Synopsis : Honey bees were eradicated on Santa Cruz Island following the introduction of Varroa. This provides some useful lessons for beekeepers on the importance of controlling Varroa.
Introduction
Honey bees are not native to North America. They were first introduced in March 1622 at Jamestown, Virginia. The bees did well and spread west, following the settlers. They finally arrived on the west coast, in Santa Clara, California, 231 years later in 1853. Of a dozen hives ordered by Christopher Shelton, a Santa Clara botanist and rancher, only one survived the journey from New York via Panama.
Shelton barely had a chance to enjoy his bees 1 as he was unfortunately killed when the steamboat Jenny Lind exploded in mid-April 1853.
Explosion on the steamboat Jenny Lind near San Francisco, California
His bees survived 2 and three hives derived from the original stock were auctioned for $110 each. This was over 20 times the price of hives on the east coast at that time and equivalent to over $4200 today 3.
Californian Channel Islands map
Bees were in demand and they continued to spread – both as feral swarms and as farmers established apiaries to help pollination and for honey production. Having reached the California coast they were then spread to the nearby islands. Bees were transported to Santa Cruz, the largest of the eight Channel Islands near Los Angeles, in the 1880’s. They flourished, but did not spread to the other Channel Islands.
Field station, nature reserves, pigs and bees
Santa Cruz Island is 250 square kilometres in area and lies ~35 km south of Santa Barbara. It is one of the four Northern Channel islands. There is a long central valley lying approximately east-west and the rocky mountainous land reaches 740 m. It has a marine temperate climate; the average low and high temperatures are 9°C and 21°C respectively and it receives about 0.5 m of rain a year. It is a good environment for bees.
From the 1880’s to 1960’s Santa Cruz Island was farmed – primarily for wine and wool, and from the 1940’s for cattle – but, after period of university geology field trips and the establishment of a field station on the island, in 1973 it became part of the University of California’s Natural Reserve System (UC NRS).
In the late 1970’s the Stanton family sold their ranching business on the island to The Nature Conservancy who subsequently bought additional land on the eastern end of the island.
Santa Cruz Island is now jointly owned by The Nature Conservancy, National Parks Service, UC NRS and the Santa Cruz Island Foundation and much of the island is used for scientific research and education.
But what about the bees?
Good question.
As a nature reserve and research station, the presence of non-native species causes a potential problem. Why go to all the expense of managing a remote island research centre if all the same species are present as on the mainland?
The Nature Conservancy therefore initiated a programme of eradicating non-native species. It took 14 months to eliminate the feral pigs, using a combination of trapping, helicopter-based shooting and the release of sterilised radio-tagged pigs to locate the stragglers 4.
But getting rid of the bees took a bit longer …
Save the bees, or not
Why get rid of the bees? Surely they weren’t doing any harm?
The introduction of any non-native species upsets the balance (if there’s ever balance) in the ecosystem. The introduced species competes directly or indirectly with those native to the area and can lead to local extinctions.
Jonathan Rosen has described5 how honey bee swarms, through occupying tree cavities previously used for nesting, probably played a major role in the extinction of the Carolina parakeet.
Pining for the fjords … a stuffed Carolina parakeet (nailed to its perch)
Competition between honey bees and native pollinators has been well studied. It is not always detrimental, but it certainly can be. Furthermore, it is probably more likely to be detrimental in a small, isolated, island ecosystem. For example, studies showed that the presence of honey bees dramatically reduced visitation of native pollinator to manzanita blossoms on Santa Cruz Island.
As part of the larger programme of non-native plant and animal eradication on Santa Cruz Island plans were drawn up in the late 1980’s to eliminate European honey bees. The expected benefits were to:
eliminate competition with native bee species (and presumably other non-bee pollinators, though these rarely get a mention 🙁 )
reduce pollination of weed species (some of which were also non-native to Santa Cruz Island)
facilitate recovery of native plant species that were reliant on native bee pollination
provide a ‘field laboratory’ free from ‘exotic’ honey bees in which comparative studies of native pollinators would be possible
Killer bees
After the plans to eradicate Apis mellifera were approved an additional potential benefit became apparent.
There were increasing concerns about the spread of Africanised honey bees which had recently reached Santa Barbara County. Although there was reasonably compelling evidence that swarms could not cross from the mainland (e.g. none of the other Northern Channel Islands had been colonised by bees) there were concerns that the Santa Ana winds might help blow drones from the mainland.
Had these drones arrived they might mate with the non-native but nevertheless local queens resulting in the spread of the dominant genes for defensiveness and absconding. The resulting swarmy, aggressive Africanised bees would cause problems for visitors and scientists working on the island (as they have for visitors to Joshua Tree National Park).
Aerial view of Santa Cruz Island
Although the introgression of African honey bee genes was used as further justification for the eradication it’s not clear whether drones could actually cross 30-40 km of open sea 6.
As an aside, there’s a current project – the amusingly named ’Game of Drones’ – running on the Isles of Scilly investigating whether drones can cross the sea between St Agnes, Tresco, Bryher, St Mary’s and St Martin’s. These are, at most, 11 km apart (northern most tip of St Martin’s to most southerly point of St Agnes) but the individual islands are only separated by 1-2 km. I would be surprised if drones could not cross that distance (at least with a strong following wind).
Killing bees
Adrian Wenner and colleagues set about exterminating the honey bees on Santa Cruz Island (Wenner et al., 2009). The process started in 1988 and ended in 2007, and was divided into four phases:
1988-1993 – location and elimination of feral colonies
2005-2007 – confirmation of the absence of honey bees
None of this is ’beekeeping’ – actually it’s the exact opposite – so I don’t intend to dwell in much detail on the work that was conducted. However, the ’94-’97 phase includes some sobering lessons for beekeepers which are worth discussing.
By the end of phase 1 the team had identified the existence (if not the location) of at least 200 colonies and eliminated 153 of them.
Remember, none of these were managed colonies in hives. They were all feral colonies occupying natural cavities in trees or rocks etc. Each colony was found using painstaking bee lining techniques similar to those described in Thomas Seeley’s book Following the Wild Bees.
Once located, nests were destroyed with methyl chloroform and the cavity sealed to prevent it being reoccupied.
Some colonies could not be accessed; in these cases acephate-laced sucrose-honey syrup baits were used. This organophosphate has delayed toxicity for bees, allowing foragers to return to the colony which in due course dies. This approach had been partially successful in eliminating Africanised bees on the mainland (Williams et al., 1989), but baits needed to be be monitored to avoid killing the other insects they attracted.
The scientists also deployed swarm traps (aka bait hives) and destroyed any swarms that moved in.
Together these interventions reduced honey bee numbers significantly – as monitored by regular observations at pollen- or nectar-rich plants – but did not eradicate them.
Let there be mite
Heavy rains in January ’93 washed out roads on Santa Cruz Island, thereby severely limiting travel around the island. In addition, the previous removal of cattle had resulted in the near-uncontrolled growth of fennel which now formed dense, impenetrable thickets.
Bee lining became impossible and the scientists had to invent more devious strategies to eliminate the residual feral colonies.
The approach they chose involved the introduction of Varroa.
Varroa was first detected in the USA in 1987 (in Florida) and became widespread over the next 5-8 years. Up until 1994 the honey bees on Santa Cruz Island were free of the ectoparasitic mite.
It was likely that they would have remained that way … there was no beekeeping on Santa Cruz Island and the location was too remote for bees to cross from the mainland (see above).
Varroa was already known to have a devastating impact on the health of honey bee colonies (Kraus and Page, 1995). It was also known that, other than its native host Apis cerana (the Eastern honey bee), Varroa did not parasitise other bee or wasp species (Kevan et al., 1991).
These two facts – host specificity and damage inflicted – suggested that Varroa could be used for biological control (‘biocontrol’) on Santa Cruz Island.
Biological control
Biological control or biocontrol is a method of controlling pests using natural mechanisms such as predation or parasitism.
The pest could be any living thing – from animals to bacterial plant diseases – present where it’s unwanted.
On Santa Cruz Island the pest was the honey bee.
In other studies (covered in a previous post entitled More from the fungi7 ) biocontrol ofVarroa has been investigated.
Control of the pest involves the introduction or application of a biological control agent. The key requirements of the latter have already been highlighted – specificity and damage.
Biological control works well when the specificity is high and the damage is therefore tightly targeted. It can be an abject failure – or worse, it can damage the ecosystem – if the specificity is low and/or the damage is widespread.
The cane toad was introduced to Australia to control infestations of greenback cane beetle (a pest of sugar cane). Cane toads were introduced in 1935 and rapidly spread. Unfortunately, cane toads can’t jump very high and so singularly failed to control the greenback cane beetle which tends to 8 stay high up the cane stems.
Female cane toad (not jumping)
But it gets worse; cane toads have a very catholic diet and so outcompeted other amphibians. They introduced foreign diseases to the native frogs and toads and – because of the poisons secreted from their skin – harmed or killed predators that attempted to eat them.
Oops.
Vertebrates are usually poor biological control agents as they tend to be generalist feeders i.e. no specificity.
But Varroa is specific and so the damage it causes is focused. The likelihood of ecosystem damage was considered low and so the mite was introduced to the island.
Introduction of Varroa
In late 1993 Adrian Wenner caught 85 foraging bees and, to each one, added a singleVarroa mite. The bees were then released and presumably flew back to their colonies … taking the hitchhiking mite with them.
Adult mites – the dark red ones you see littering the Varroa tray after you treat with Apivar – are mated females.
Due to their incestuous lifestyle a single mite is sufficient to initiate a new infestation.
The mated adult female mite parasitises a honey bee pupa and produces a series of young; the first is male, the remainder are female. You’re probably reading this before the 9 pm watershed so I’ll leave it to your lurid imagination to work out what happens next (or you can read all the sordid details in Know your enemy).
The presence of honey bees – determined by successful swarm trapping or field observation at likely sites – was then regularly monitored over the next four years.
Swarm numbers remained largely unchanged until 1996 and then dramatically decreased.
Numbers of new swarms on Santa Cruz Island 1991 – 2005. Varroa introduction indicated.
It’s worth noting that during ’94-’96 over 70 swarms were found in natural sites or bait hives. There must have been a significant number of established colonies in 1993 to produce this number of swarms.
But, from 1997 it all stopped … only a single swarm was subsequently found, in a natural cavity in 2002.
Monitoring and confirmation of eradication
From 1998 to 2004 the scientists continued to actively monitor the island for honey bees, focusing on 19 areas rich in natural forage. Although honey bees were found – in decreasing numbers – there were too few to attempt bee lining to locate their colonies.
At the sites being monitored, bees were detected 9, 7, 4, 2 and 1 times respectively in the 5 years from 2000 to 2004. After that, despite continued monitoring, no more honey bees were detected.
The final phase of the project (’05-’07) confirmed the absence of honey bees on Santa Cruz Island.
Whilst, as a scientist, I’m a firm believer that ’absence of evidence does not mean evidence of absence’, as a beekeeper I’m well aware that if there are no scout bees, no swarms and no foragers (when I search in likely places) then there are no honey bee colonies.
Lessons for beekeepers
I wouldn’t have recounted this sorry tale – at least from a beekeeping perspective – unless I thought there were some useful lessons for beekeepers.
There are (at least) three.
The first relates to Varroa resistance, the second to Varroa transmission in the environment and the last to ‘safe’ levels of Varroa. All require some ‘arm waving guesstimates’9, but have a good grounding in other scientific studies.
Varroa resistance
There wasn’t any.
At a very conservative estimate there were at least 20 colonies remaining on Santa Cruz Island in 1995. I say ‘conservative’ because that assumes each colony generated two swarms that season (see graph above). In studies of other natural colonies only about 75% swarm annually, meaning the actual number of colonies could have been over 50.
The numbers – 20 or 50 – matter as they’re both much higher than the number of colonies most beekeepers manage (which, based upon BBKA quoted statistics, is about 5).
Whether it was 20 or 50, they were all eliminated following the introduction of 85 mites. Colonies did not become resistant to Varroa.
This all took a few years, but – inferring from the swarm numbers above – the vast majority of colonies were killed in just two years, 1994 and 1995. This timing would fit with numerous other studies of colony demise due to mites.
Wenner estimates that only 3 colonies survived until 2001.
Leaving small numbers of colonies 10 untreated with an expectation that resistance – or even tolerance (which is both more likely and not necessarily beneficial) – will arise is a futile exercise.
I’ve discussed this before … it’s a numbers game, and a handful of colonies isn’t enough.
Varroa spread
Wenner doesn’t elaborate on where the foragers were captured before he added the mites. If I was going to attempt this I’d have chosen several sites around the island to ensure as many feral colonies as possible acquired mites … let us assume that’s what he did.
However, with 85 mites piggybacking on returning workers, and somewhere between (my guesstimated) 20 to 50 colonies, I think it’s highly likely that at least some colonies received none of this ’founding’ mite population.
Yet almost all the colonies died within two years, and those that did not subsequently died with no further intervention from the scientists. We don’t know what killed off the last surviving colonies but — and I know I’m sticking my neck out here – I bet it was the mites.
This is compelling evidence for the spread of Varroa throughout the island environment, a process that occurs due to the activities of drifting and robbing.
If a neighbouring apiary to yours has mites some will end up in your hives … unless you are separated by several kilometres 11.
The transmission of mites in the environment is a very good reason to practice coordinated Varroa control.
One mite is all it takes
But, just as I’ve argued that some colonies may have received none of the founding mites, I’m equally sure that others will have acquired very small numbers of mites, perhaps just one.
And one mite is all it takes.
Without exceptional beekeeping skills, resistance in the bee population or rational Varroa control12 there is no safe level of mites in a colony.
The more you prevent mites entering the colony in the first place, and the more of those that are present you eradicate, the better it is for your bees.
Here endeth the lesson 😉
Note
It’s worth noting that island populations do offer opportunities for the development of Varroa resistant (or tolerant) traits … if you start with enough colonies. Fries et al., (2006) describes the characteristics of the 13 surviving colonies on Gotland after leaving about 180 colonies untreated for several years. I’ve mentioned this previously and will return to it again to cover some related recent studies.
References
Fries, I., Imdorf, A. and Rosenkranz, P. (2006) ‘Survival of mite infested (Varroa destructor) honey bee (Apis mellifera) colonies in a Nordic climate’, Apidologie, 37(5), pp. 564–570. Available at: https://doi.org/10.1051/apido:2006031.
Kevan, P.G., Laverty, T.M. and Denmark, H.A. (1990) ‘Association of Varroa Jacobsoni with Organisms other than Honeybees and Implications for its Dispersal’, Bee World, 71(3), pp. 119–121. Available at: https://doi.org/10.1080/0005772X.1990.11099048.
Kraus, B. and Page, R.E. (1995) ‘Effect of Varroa jacobsoni (Mesostigmata: Varroidae) on feral Apis mellifera (Hymenoptera: Apidae) in California’, Environmental Entomology, 24(6), pp. 1473–1480. Available at: https://doi.org/10.1093/ee/24.6.1473.
Wenner, A.M., Thorp, R.W., and Barthell, J.F. (2009) ‘Biological control and eradication of feral honey bee colonies on Santa Cruz Island, California: A summary’, Proceedings of the 7th California Islands Symposium, pp. 327–335. Available as a PDF.
Williams, J.L., Danka, R.G. and Rinderer, T.E. (1989) ‘Baiting system for selective abatement of undesirable honey bees’, Apidologie, 20(2), pp. 175–179. Available at: https://doi.org/10.1051/apido:19890208.
Synopsis : The features of a successful bait hive are well known. However, they are not absolutes. The more desirable features your bait hives offer the more successful they should be, but both the bees and the beekeeper can make compromises through necessity or preference.
Introduction
I gave a talk on bait hives to a friendly group of beekeepers from Westerham last week. Westerham is near Sevenoaks in Kent, a rich agricultural area with lots of fruit growing and hops for the brewing industry.
And, as you will see shortly, lots of beekeeping.
One of the messages I try and get across in my talk on bait hives is that it is a remarkably successful way to capture swarms … and a whole lot less work than teetering precariously on a step ladder holding a skep.
However, success involves two things:
understanding the needs of the swarm, and
overcoming the doubt that such a passive activity – essentially putting a box in a field – can be so successful.
But I’m getting ahead of myself.
Some readers may not know what a bait hive is.
Smelling faintly of propolis and unmet promises
The post this week is not intended to be a comprehensive account of how you should prepare and set out bait hives. I’ve covered this topicad nauseam before. Instead, I’m going to try and convince you that, although it is a passive activity, if you do things correctly you are very likely to succeed.
And then, in the second half of the post, I’ll discuss an interesting question (and my – possibly less interesting – answer) from one of the Westerham beekeepers that is a nice illustration of some of the compromises that beekeeping entails.
Bait hives and swarm traps
A bait hive is an artificial nest site placed somewhere suitable to attract a swarm.
In the US these are often called ‘swarm traps’.
I don’t think either name is perfect … a bait hive doesn’t involve ‘bait’ 1 and a swarm trap doesn’t really ‘trap’ the swarm as they are free to leave again.
That they (almost) never do is rather telling … I touch on this in my post on absconding.
A bait hive deployed in mid-April in good time for the swarm season ahead
A bait hive possesses the features that scout bees look for when searching the environment for a new nest site. Essentially these are the following:
a 40 litre void
smelling of bees
with a small entrance situated near the bottom of the void
facing south
shaded but clearly visible
and located at least 5 metres above the ground
The majority of these features were defined by studies of natural swarms and in experiments by Thomas Seeley described in his book Honeybee Democracy3.
Conveniently a beekeeper can meet these needs by assembling the following and placing it somewhere suitable:
a brood box with a roof, a solid floor and a small entrance
filled (completely or partially) with foundationless framesplus one old dark brood frame
a drop or two of lemongrass oil
Surely it can’t be that easy?
Yes it can … and it is.
But let’s first try and overcome the impression that something as simple and passive as a box in a field will even be found by scout bees, let alone selected by them as the new nest site for the swarm.
If you build it, they will come
In the 1989 file Field of Dreams an Iowan farmer, Ray Kinsella (played by Kevin Costner), follows his dream of creating a baseball field in his corn field. The oft misquoted ’If you build it, they will come’ from the movie really means that if you put your doubts aside you will succeed 4.
Kinsella was attracting disgraced baseball players from 50 years earlier … all your bait hive needs to do is attract a swarm from a nearby mismanaged 5 hive.
Which is a whole lot easier.
Nearby hives
So how many nearby hives are there? How many are likely to swarm? And how near is nearby?
Let’s return to the lovely blossom-filled orchards around Westerham in Kent for some specifics.
The National Bee Unit’s Beebase has information on the number of apiaries within 10 km of any of your own apiaries that are registered.
Within a 10 km radius of Westerham there are 247 other apiaries. That’s a lot 7, but I’ve no doubt it reflects the excellent forage in the area, and the unstinting efforts of Kent beekeeping associations to train more beekeepers.
How many hives do these apiaries contain? I have to start guessing here as mere mortals can’t mine that sort of information from Beebase.
Firstly, it’s a sensible minimum number of hives to co-locate in an apiary. Secondly, with about 250,000 managed colonies in the UK and about 50,000 beekeepers, if we assume that they are evenly distributed 9 it works out as a rather neat 5 hives per apiary.
Which means that in the 314 square kilometres within a 10 km radius of Westerham there are over 1200 hives, which equates to almost 4 hives per square kilometre (the precise number is 3.931, but you’ll appreciate I’m in arm waving mode here).
How far do scout bees, er, scout?
To answer this we can safely (but briefly) disengage arm waving mode.
Scout bees fly from and return to the bivouacked swarm. They then communicate with other scout bees by performing a waggle dance on the surface of the bivouac.
Thanks to Karl von Frisch we can decipher the waggle dance, which includes both directional and distance information.
And from doing exactly that we know that scout bees survey the landscape for at least 3 km from the swarm.
Hive density, swarms, scout bees and bait hives (see text for details)
In the diagram above a typical area investigated by scout bees is indicated by the pale yellow circle. The red dot indicates the bivouacked swarm. The grid in the background is 1 km squares.
The bait hive is in blue in the centre of a circle of radius 10 km. The smaller dotted circle represents the maximum distance from which a scout bee would travel to find the bait hive 10 .
Let’s put some numbers on that.
Assuming the average hive density at Westerham is about 4 per km2 and that apiaries and hives are evenly distributed, there will be 111 hives within the smaller dotted circle of radius 3 km 11 .
If any of those hives swarm, their scout bees could or should find the bait hive.
And, if they like the bait hive enough, they might persuade their fellow scouts to check it out and – in due course – together lead the swarm to the bait hive.
The final piece of the jigsaw necessitates re-engaging arm waving mode …
Ready?
What proportion of hives swarm each year?
Over the last several years I would say that the majority of my full-sized production colonies have tried to swarm each season. By ’tried’ I mean produced charged queen cells which necessitated me employing swarm control.
Queen cells …
The vast majority of these colonies did not swarm … because the swarm control was successful.
But I’ve certainly lost a few swarms over the years 🙁
About 80% of free-living colonies studied by Thomas Seeley in the Arnott Forest swarmed each season. There are reasons to think that this may be higher than normal 12, but possibly not much higher than large, healthy managed colonies.
So, if 80% of managed colonies around Westerham ‘try’ and swarm each season, the actual number of swarms is a reflection of how well trained the beekeepers of Kent are … and, for those who have kept bees for several seasons, how effective they are at swarm control.
And, whilst I’m sure the training is excellent and the swarm control is diligently applied, I’m equally sure that many swarms are lost 😉
A small swarm …
If we assume that only 10% of colonies swarm, that’s still 11 swarms a season within range of a bait hive placed anywhere within the larger 10 km radius circle.
And I’d wager my favourite hive tool 13 that it’s more than 10% 😉
Evolution of nest site preferences
The preferences shown by scout bees 14 have evolved because swarms that move into nest sites like these survive better.
If they survive, they are also more likely to reproduce (swarm), so passing on the genes that were instrumental in creating the bees that selected those particular features in a nest site.
This does not mean that the nest site features are absolutes.
For example, a 35 litre or 45 litre void is likely to be just as attractive.
In fact, the scout bees may not be able to discriminate between these anyway.
However, although a tiny 10 litre void or a cavernous 100 litre space is less attractive, it does not mean that a swarm won’t select a cavity of these volumes and move in.
Whether it does or not depends upon what other choices are available and upon the poorly understood (at least by me) ranking of the importance of the various features of the nest sites.
However, if the bees rank void volume as relatively unimportant, and your bait hive was perfect in all other regards, then perhaps they would choose to move in.
Compromises by bees
In reality, they probably would not move in to a 10 litre bijou bait hive, perfect in all other regards, as the volume available is the primary determinant of how big the colony can get, how much brood it can rear and how much pollen and nectar it can store.
Furthermore, the natural environment (in which I include your bait hive placed in the landscape) does not offer simple choices in which only individual features vary.
Almost everything varies … even two apparently similar bait hives are likely to occupy locations with more or less exposure, or greater or lesser shade, between which the scout bees will choose.
And natural cavities, in trees, church towers or compost bins 16 are likely to vary in many or all of the features judged by scout bees.
The scout bees make their decision based upon the sum of the overall desirability of a nest site, which is undoubtedly influenced by their ranking of which features are more or less important.
Perhaps they can cope with a west facing entrance that’s a bit larger than they would prefer if the shade is good, the space is the right size and it pongs nicely of bees.
It’s effectively a compromise.
But remember that your bait hive has to compete with the wealth (at least in some landscapes) of natural nest sites.
In this regard, you have an advantage. The more of the desirable features you offer, the more desirable the nest site should be.
Q&A
Which, by a typically long and circuitous route, brings me to the interesting question from a Westerham beekeeper 17 following my bait hive talk:
If scout bees prefer bait hives with solid floors does this mean that bees prefer solid floors over open mesh floors?
I can’t remember the exact wording of my answer but know it involved reference to the draughtiness of the space. I hope I also mentioned the amount of light inside the void, but can’t be sure.
A more complete answer would be that bees aren’t too worried about a draughty space, at least one with small holes, cracks or fissures, as these can be filled with propolis. However, they do prefer a dark space, and a bait hive with an open mesh floor would presumably be too well illuminated for the scout bees.
I think this reflects the evolution of nest site choice.
Bees have evolved to prefer (select) dark spaces as these – by definition – don’t have large holes that let light or more importantly bears, honey badgers and robbing bees, in.
Natural cavities don’t have mesh floors. Indeed, stainless steel mesh isn’t something that bees will have experienced for the first few million years of their evolution.
Therefore, it’s not that they prefer solid floors over mesh floors, it’s that they prefer dark, secure spaces over well lit voids that may well be difficult to defend.
Covered OMF … as bees prefer bait hives with solid floors
But, when setting out your bait hives there’s an easy fix … simply cover an open mesh floor with a piece of cardboard or Correx. You can always remove it again once the bees have arrived.
What do the bees want?
But do scout bee preferences tell us something about what the colony, once established, prefers?
Not necessarily, at least with regard to the closed or open nature of the floor.
Let’s accept that that scout bees (and therefore swarms) prefer a solid floor for the reasons given above. That is not the same as it being an indication that the established colony would prefer a solid floor over an open mesh floor.
If they did, what differences in the behaviour of the bees would you observe?
I think you’d see more colonies absconding from hives with open mesh floors than those with solid floors. I’m not aware of any data showing that colonies on solid floors abscond less. I don’t use solid floors and have never had a full colony abscond.
The bees would cover and seal the mesh with propolis. Again, I’ve never seen this in my own hives, though I regularly see them blocking gaps over the colony with propolis.
There are enough beekeepers still using solid floors, and even some reverting from mesh floors to solid floors. However, I don’t think I’ve ever heard a beekeeper moving (or moving back) to solid floors to reduce the number of colonies that abscond.
Have you?
Compromises by beekeepers
Finally, let’s return to that list of desirable features sought by the scout bees.
Remember that they are not absolute.
Just because a bait hive faces west doesn’t mean it will be ignored by scout bees. I’ve attracted two swarms in successive days to one west facing bait hive in my garden. The same bait hive caught a swarm two months earlier as well 18.
By facing the bait hive west I got a better view of the entrance … it was a compromise that suited me.
Under offer …
I regularly use two stacked supers (in place of a brood box) as a bait hive. These have been very effective, despite having about 25% greater volume 19.
Again, this is a compromise that suits me. It allows me to use some supers that I dislike because they have an overhang/rebate and are infuriatingly incompatible with my other equipment.
I also never site bait hives more than 5 metres above the ground.
In fact, I almost always site them at knee height.
Bees have probably evolved to choose high altitude nest sites to avoid predation by bears.
Global (current and historic) distribution of the brown bear
There are no bears in Scotland, at least not wild ones, though historically they were present. Their absence isn’t why I don’t bother to place my bait hives up trees.
I want to be able to observe scout bee activity easily. More importantly, I want to be able to safely move the hive late in the evening of the day the swarm arrives.
I can do both these things much better with the hive on a hive stand.
It probably makes the bait hives slightly less attractive to the scout bees, but it’s a compromise I’m willing to make as it improves my enjoyment of the bees and simplifies my beekeeping.
If I wanted to climb ladders I’d go out collecting bivouacked swarms in a skep 😉
