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Do free-living honey bee colonies actually outnumber managed hives by 3:1? How was this decided, what assumptions have been made and why don’t I see occupied timber after I’m out strolling?
Introduction
Why are the copses, coppices and thickets of the UK (or for that matter Europe or a lot of North America) not full of massive numbers of free-living honey bee nests?
As a biologist who has labored on Varroa and the devastating penalties of mite infestation my reply can be that the introduction of this ectoparasite to a honey bee inhabitants – whether or not managed or free-living – gives the reason.
The place are all of the bees?
The reported annual losses by beekeepers – recurrently ~20% and sometimes exceeding 30% in large-scale surveys – often cite Varroa as a reason behind the losses and so helps the view that Varroa has a devastating affect on honey bees populations.
I stay sceptical of the strategies utilized in these annual surveys, their accuracy and the conclusions that may be drawn from them (however I don’t disagree concerning the significance of Varroa) .
Does a discount in losses (bear in mind these are self-reported and unverified) from 27% to 22% symbolize a marked enchancment in beekeeping?
After all not … it’s simply ‘noise’.
However, the frequency with which Varroa or the viruses it transmits – predominantly deformed wing virus (DWV) – is talked about as the reason for the losses incurred clearly (albeit comparatively unscientifically) helps the view that Varroa is unhealthy information for bee populations.
After all, at a person stage, many beekeepers be taught this lesson the arduous method after they lose their colonies overwinter.
Santa Cruz Island
After which there was using Varroa to eradicate honey bees on Santa Cruz Island. Honey bees had been launched to the island within the mid-19th Century; inevitably swarms have been misplaced and have become established as free-living colonies.
As half of a bigger programme of non-native plant and animal eradication on Santa Cruz Island plans have been drawn up within the late 1980’s to remove honey bees.
Aerial view of Santa Cruz Island
Bodily destruction of colonies and nest websites over a 5 12 months interval diminished the honey bee numbers by ~75%. Nonetheless, the stragglers – most likely 50+ colonies – have been in inaccessible places.
Slightly than open-feeding utilizing poison-laced baits (which could have devastated native insect inhabitants as properly) Varroa was launched. For two-3 years honey bees remained current however then, in 1997, they successfully disappeared from the island.
This timing suits with the identified affect on Varroa the place, if unchecked, mite quantity construct as much as devastating ranges over a few seasons.
After 1997 just one colony was discovered (and destroyed) and no honey bees have been detected on the island since 2004.
So … the introduction of Varroa prompted the eradication of your complete honey bee inhabitants.
Nicely … not fairly.
- Firstly, 75% of the colonies had already been ‘manually’ destroyed.
- Secondly, all colonies have been derived from a small variety of founding colonies so inbreeding – and the ensuing lack of colony health – was most likely a contributing issue (and sure would develop into extra vital as colony numbers diminished).
- Lastly, being an island, the inhabitants was ‘closed’ with no probability of the introduction of some revitalising novel genetics.
Rebounding colony numbers
Though Varroa most likely helped ‘end off’ the Santa Cruz honey bees there are different examples the place free-living colony numbers, though most likely initially diminished (maybe massively) after Varroa introduction, subsequently rebound.
Free-living colonies within the Arnot forest
Thomas Seeley has studied honey bees within the Arnot forest in western New York State for a few years. These research included surveying colony numbers and distribution in 1978, 2002 and 2011, a 33 12 months interval spanning the introduction of Varroa (Seeley, 2007).
Notably, colony density remained broadly unchanged (at ~1/km2) after the introduction of Varroa, with the caveat that I’m unsure exactly when the mite arrived within the forest (it arrived in New York State in 1987). A precipitous drop in colony numbers might have occurred however been adopted by a restoration interval by which numbers of the now mite-infested colonies elevated to pre–Varroa ranges.
In a method this doesn’t matter … the purpose is that there stays a free-living inhabitants of honey bees at comparable densities to these earlier than the mite was launched.
The absolute density – with colonies spaced ~1 km aside – probably displays the supply of nest websites (which I’ll focus on subsequent week) or the forage availability within the surroundings.
Blenheim bees
The Arnot forest bees are most likely a number of the greatest studied when it comes to numbers, distribution, pathogen ranges and potential mechanisms of tolerance or resistance to Varroa, however they’re not at all the one free-living, mite-infested inhabitants of honey bees .
‘Blenheim bees’ article within the Grauniad, 7-11-21
Nearer to residence, I’ve beforehand mentioned ‘historical’ populations of honey bees dwelling – unmanaged – in woodland close to Oxford, UK. Whether or not they’re historical or not (and I think not, each for causes defined in a observe up put up and since I’ve seen nothing extra concerning the DNA evaluation of their genetic ‘uniqueness’) doesn’t alter the truth that there are bees in some woods … which brings me again to the opening sentence of the introduction.
Definitions
I used to be cautious in my selection of phrases for the opening sentence of the primary paragraph.
Why are the copses, coppices and thickets of the UK (or for that matter Europe or a lot of North America) not full of massive numbers of free-living honey bee nests?
That is the primary of two associated posts on feral bees within the surroundings and with writing effectivity in thoughts I’m utilizing the identical opening sentence for each.
Slightly than dwell on the identified affect of Varroa and the viruses it transmits, I as an alternative wish to focus on the numbers and placement of free-living honey bee colonies.
I additionally wish to keep away from the thorny subject of whether or not the bees that are current within the woods are latest escapees or have been free-living for many years (or centuries as is usually claimed, regardless of the actual fact there could also be no supporting proof ).
Nonetheless, a few of these distinctions are essential.
Wild vs. feral
Are the any ‘wild’ honey bees in continents the place massive numbers of managed colonies exist? Varroa can decimate honey bee populations, the mite has a near-global distribution and beekeepers recurrently lose swarms.
Since there are managed colonies in all continents besides Antarctica the opening query of this part may very well be simplified to ’Do wild honey bees (Apis mellifera) nonetheless exist?
I don’t wish to get slowed down within the distinction between ‘wild’ colonies and those who have escaped administration – by swarming – and will maybe subsequently be thought-about ‘feral’, outlined by the OED as:
Of an animal: Wild, untamed. Now usually utilized to animals or vegetation which have lapsed right into a wild from a domesticated situation.
Besides in fact, bees aren’t actually domesticated (once more, OED’s definition, my daring textual content):
Of an animal: that has been tailored to reside in shut affiliation with and for the advantage of people, esp. by means of selective breeding over time to alter its behaviour, look, and many others.; tamed, not wild; stored as livestock or as a pet.
What a minefield!
Free-living
In a method that is all semantics. When does a misplaced swarm (whether or not initially thought-about feral or not) develop into wild?
As soon as it reproduces (swarms), presumably the next 12 months?
Or after dwelling unmanaged for 3 generations, or 30, or 300?
For that reason astute readers will be aware that I’ve used the time period ‘free-living’ for almost all of this put up.
The time period encapsulates two essential ideas;
- free i.e. not managed or maintained.
- dwelling i.e. not dying … a elementary distinction, essential each to the bees and in our understanding of their standing. Many research present that just lately escaped swarms often die inside a 12 months or so. For instance, contemplate the colonies populating black woodpeckers nests in German beech forests (Kohl and Rutschmann, 2018). A free-living inhabitants must be self-sustaining and never reliant on the annual inflow of swarms misplaced from (mis)managed hives.
So, that’s what I’ll attempt to follow.
That is maybe a pity because the paper I wish to focus on for the rest of the put up is titled:
Density of untamed honey bee, Apis mellifera, colonies worldwide.
Oops.
This research (Visick and Ratnieks, 2023) is a meta-analysis of wild free-living honey bee colony densities around the globe.
A meta-analysis entails the ‘statistical integration of proof from a number of research that deal with a standard analysis query’ . When attempting to attract broad conclusions it’s thought-about extra highly effective than single case and even well-controlled experiments.
For instance might you draw any conclusions concerning the numbers of free-living honey bee colonies in North America if the solely information you had are from the 8-10 colonies current within the small area of the Arnot forest that Thomas Seeley studied?
Nicely, you may draw conclusions, however they most likely wouldn’t be very informative … or correct.
However for those who had a dozen research from consultant and dispersed areas of North America, ideally performed by scientists utilizing comparable strategies and with the identical rigour, then issues begin to get a bit extra significant.
Or, higher nonetheless, 200 research.
The mix of enormous numbers of research and using comparable and quantified strategies can produce actually compelling proof. That is the best way some drug trials are analysed and validated, in research costing tens of thousands and thousands of {dollars} .
However we don’t reside in an excellent world and honey bee analysis entails tens of {dollars}, not tens of thousands and thousands , so we have now to deal with smaller numbers of research performed by completely different scientists utilizing a wide range of strategies.
Visick and Ratnieks (2023) reviewed 40 research on colony density from 41 places around the globe. These varied research have been revealed in ~55 papers over a 50 12 months interval.
Estimates of free-living honey bee populations
Colony density was decided utilizing direct (commentary, bee-lining, native data) or oblique (primarily genetic evaluation of employees or of drones from drone congregation areas) strategies and associated to the area by which the survey was performed, the space surveyed, the native local weather and managed colony numbers
Free-living and managed colony densities
Imply regional densities have been extremely variable, from 0.26/km2 in Europe to six.8/km2 in Africa. In North America the imply density was 1.4/km2.
Survey space
Density was inversely associated to space surveyed (beneath above) which can mirror survey bias; for instance, smaller bee-rich areas might have been chosen, or the hassle wanted to find colonies in massive areas was not expended.
Free dwelling colony densities: affect of temperature (left) and survey space (proper)
Evaluate the 2 diagrams beneath. On the left a ‘biased’ survey focusing solely on the world with the pink border – which is 1/16th the world of the blue sq. – would grossly overestimate colony density throughout the blue border. Conversely (on the precise) since discovering simply one colony is time consuming, massive survey areas threat lacking nests, resulting in an underestimate of colony density.
Biased surveys (left) and incomplete surveys (proper)
Survey areas of <1 km2 have been excluded as some had wildly unrealistically excessive colony densities.
However what’s the ‘survey space’ in research which ‘not directly’ measured colony density by trapping employees or drones and analysing their genetic variety? For these the world was assumed to be 4.5 km2 for employees or 2.5 km2 for drones. These figures have been derived from common queen or drone mating distances of 1600 m or ~900 m respectively .
Regional temperatures
Colony densities have been associated to temperature (see graph above), peaking at a imply annual temperature of 23°C.
Temperature influences each the flexibility of bees to forage and the supply of forage in the course of the 12 months. Sub-tropical areas are more likely to have extra forage obtainable for longer durations of the 12 months and have temperatures higher fitted to foraging (which different research have proven is ~20°C).
Nonetheless, in actually sizzling areas colony density was diminished, presumably because of different elements like drought or the cooling effort wanted to forestall comb collapse.
What’s the imply temperature within the UK?
I’ve assumed that Visick and Ratnieks are utilizing the arithmetic imply of the temperature, somewhat than another type of imply and/or peak daytime temperature. A part of the rationale I’ve assumed that is I’ve figures for UK common temperatures:
Met Workplace imply annual temperature information
It varies from 12 months to 12 months by a level or so, it varies geographically and (although not proven on this determine) it’s inexorably rising. 2003 was fairly typical for the final 20 years, 2013 was unusually chilly and 2023 hotter than regular (not less than for the South and Midlands).
At 11-12°C our imply annual temperatures are properly beneath optimum for honey bees. One cause the temperature is so low is due to our protracted cool/chilly winters.
Beekeepers know – and sure some might be reminded of that is the following few weeks – that these winters can considerably scale back colony survival (subsequently additionally lowering free-living colony densities).
Assumptions (once more) and conclusions
Inevitably, in a research contemplating world free-living honey bee densities, based mostly upon work spanning not less than 50 years from a number of authors utilizing a wide range of survey strategies, there are a lot of assumptions made.
For instance, virtually half of the European research have been performed in massive geographic areas the place colony numbers have been most likely underestimated.
However, if the regional colony densities are relevant throughout every area, this meta-analysis means that whole free-living colony numbers could also be two to 3 occasions greater than world managed hive numbers (which at present exceed 102 million).
That sounds surprisingly excessive … however then I reside in one of many largely blue areas within the maps above, so have a tendency to not see too many colonies surviving outdoors a poly hive.
The UK has an space of ~250,000 km2. Assuming the free-living colony density is 0.26/km2 that will imply the ‘copses, coppices and thickets’ of this nation harbour about 65,000 colonies. For comparability, present numbers of managed colonies exceed ~288,000 (i.e. a density of ~1.2/km2).
Strolling within the woods
Though I’ve not often intentionally looked for free-living colonies, I’ve walked many, many miles in Scotland and the Midlands over the past couple of many years … and I’m fairly observant.
The Midlands significantly are densely populated with managed hives (~275 apiaries inside 10 km of mine, implying a managed hive density of over 4/km2) and the beekeepers there inevitably lose massive numbers of swarms . Regardless of this, I solely not often discovered free-living colonies, and their density would most likely have been a lot lower than 0.26/km2.
The few I’ve discovered have virtually all been in man-made constructions; church towers, college halls of residence, a struggle memorial and many others., with none that I can bear in mind in ‘copses, coppices and thickets’.
Maybe I’m wanting within the fallacious place?
I’ll return to that subject subsequent week.
North America
Free-living colonies in North America have been predicted to outnumber managed hives 7:1, with the densities being 1.4 and 0.2/km2 respectively.
It’s honest to say that there was appreciable scepticism about a few of these estimates on Bee-L, a dialogue board largely populated by naturally aporetic scientific-leaning beekeepers based mostly largely within the US.
Fairfax, South Dakota.
Southern California may include massive numbers of free-living colonies, however absolutely not the Pacific Northwest, the Dakota’s, Minnesota and Michigan (consider the winters!), or the damp North Atlantic seaboard?
Inevitably the Bee-L dialogue degenerated ended up debating the definition of ‘wild’, ‘feral’ and ‘free-living’.
Africa
Africa had an analogous free-living to managed colony ratio to North America, however there are extra of each.
The biology of the honey bee (Apis mellifera scutellata) in Africa is attention-grabbing. The excessive temperatures imply that brood rearing and comb constructing can happen year-round … if there’s enough forage and/or water obtainable.
When there’s, the colonies increase however then are likely to swarm earlier than they get very massive.
Nonetheless, when forage or water are limiting – for instance because of an area drought – the colony migrates. It absconds, flying 10’s of kilometres to areas with higher situations.
The ‘swarminess’ of scutellata most likely accounts for the massive variety of free-living colonies. It additionally explains why beekeepers can hang around log hives with an expectation they are going to be occupied.
Higher honeyguide
Lastly, suppose again to my put up two years in the past on honeyguides . It’s possible that this mutualistic relationship couldn’t have developed with out massive numbers of free-living honey bee colonies.
The place are all these free-living colonies?
How do these calculations of free-living honey bee colonies assist?
If correct, or not less than broadly consultant, they are going to assist in figuring out their contribution to ecosystem companies i.e. human advantages from the pure surroundings/ecosystem. For instance, crop pollination.
Equally, they might assist perceive the affect of local weather change, pathogen introduction and unfold, or pure choice for illness resistance.
Nonetheless, if they’re wildly inaccurate they’re more likely to result in incorrect conclusions about these or different issues. Comply with-up surveys are wanted to validate each the outcomes that this meta-analysis are based mostly on, and to find out how usually relevant the outcomes are.
Some readers might discover that, paradoxically contemplating my remark about extrapolating North American numbers from the Arnot forest information, they’re about the identical!
Even and uneven distributions
The regional averages I’ve quoted are a bit deceptive. A determine of 0.26/km2 in Europe does not imply it’s best to look forward to finding one free dwelling colony in each 4 km2 searched (left, above). As an alternative, the distribution might be uneven, with native concentrations interspersed by massive empty areas (proper, above).
Which of these ‘copses, coppices and thickets’ are occupied?
Within the put up subsequent week I’ll focus on a method of probably discovering these ‘native concentrations’, with out having to go looking all of the empty areas.
References
Kohl, P.L., and Rutschmann, B. (2018) The uncared for bee timber: European beech forests as a house for feral honey bee colonies. PeerJ 6: e4602 https://peerj.com/articles/4602.
Seeley, T.D. (2007) Honey bees of the Arnot Forest: a inhabitants of feral colonies persisting with Varroa destructor within the northeastern United States. Apidologie 38: 19–29 https://doi.org/10.1051/apido:2006055.
Visick, O.D., and Ratnieks, F.L.W. (2023) Density of untamed honey bee, Apis mellifera, colonies worldwide. Ecology and Evolution 13: e10609 https://onlinelibrary.wiley.com/doi/abs/10.1002/ece3.10609.
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