Synopsis: Historic and veteran bushes embrace many sufficiently big to accommodate a colony of free-living honey bees. Right here is a few science and hypothesis on the bushes, the bees and what to search for.

Introduction

Why are the copses, coppices and thickets of the UK (or for that matter Europe or a lot of North America) not stuffed with massive numbers of free-living honey bee nests?

Deja vu? …

Don’t fear, you’re not shedding your thoughts. That was precisely the identical sentence I began the publish with final week.

It’s a sound query.

In the event you settle for the numbers I offered final week – remembering it was a meta-analysis of a comparatively small variety of experimental research yadda yadda – then there are massive numbers of free-living honey bee colonies someplace on the market within the atmosphere.

Throughout us.

It’s a pleasant thought isn’t it?

What number of?

Properly, it relies upon a bit on the way you calculate it.

Calculators out!

The density of free-living colonies in Europe was 0.26/km² and managed colonies outnumbered them about 4:1. Calculated from the world (~243,000 km²) this works out at 63,000 free-living colonies within the UK. The estimated hive quantity right here is 288,000; utilizing that as the premise for the calculation offers a solution of 72,000 free-living colonies scattered round this little island.

Let’s break up the distinction and name it ~67,000.

And for North America (the place the free-living colony density was 1.4/km²)? Utilizing the identical form of calculations issues aren’t in fairly such good settlement. The North American continent has an space of ~24.7 million km² and comprises ~3.4 million managed colonies. Based mostly upon space, it’s predicted that North America comprises ~34.6 million free-living colonies. From managed colony numbers (that are outnumbered 7:1) the quantity could be ~24 million.

Once more, let’s break up the distinction and assume it’s 29 million free-living colonies.

Keep in mind, there are all kinds of assumptions made within the preparation of those numbers however, no matter method you have a look at them, it’s a heck of lots of bees.

So, the place are they?

Northern climes and opposed environments

Latest proof recommend that Apis mellifera developed in Europe and unfold to southeast Europe and Asia Minor (Carr, 2023), splitting into the assorted sub-species like carnica, ligustica and others. The honey bee is native to Europe, however was launched to North America (in 1622; Carpenter and Harpur, 2021).

Regardless of originating in a northern local weather, honey bees can’t naturally survive in a number of the most northerly areas of those two continents – the winters are too lengthy and/or the forage obtainable is inadequate.

As well as, there are hotter areas in each continents which might be largely or utterly unsuitable for honey bees; for instance, they’re too dry, have too little forage all through the season or lack any pure nest websites.

Due to this fact, the pure distribution of honey bees can be ‘patchy’, greater the place situations are beneficial, low or absent elsewhere. Within the diagram above, some areas have excessive concentrations of nest websites (blue), others, not a lot (inexperienced) and a few, none in any respect (pink).

All that is additional sophisticated by the presence of managed colonies that share the identical atmosphere. Misplaced swarms from these managed colonies turn into established in pure nest websites, most will perish however some might survive (evolving from managed to feral to free-living, or at the very least being outlined as akin to time passes).

All of which is a convoluted method of claiming that the colony densities of 0.26/km² or 1.4/km² will turn into much less and fewer correct as you have a look at smaller areas … like throughout a stroll by the countryside on a summer season afternoon.

However which areas are most probably to have free-living colonies?

Bosky groves

The honey bee developed to nest in cavities. Due to this fact, until all these free-living colonies are in caves or man-made buildings (e.g. previous church buildings) they’re most probably to be occupying cavities in bushes.

James Joyce used the time period ‘bosky grove’ in Ulysses …

“of bosky grove and undulating plain and luscious pastureland of vernal inexperienced”

Bosky means ‘filled with thickets or brush’, and I intentionally used ‘thickets’ in my opening sentence. I didn’t use bosky as I needed you to proceed studying the publish 😉

Bosky groves, in addition to “copses, coppices and thickets” (and specifically the final two), suggest immature woodland, missing many or probably any substantial bushes outlined by way of their top or – extra importantly so far as bees are involved – their girth.

Why girth?

As a result of a honey bee nest is sort of a big construction and a small tree, or perhaps a medium sized tree, is unlikely to have ample girth to accommodate it. And the one method the tree can have acquired ample girth is by rising for a very long time.

Therefore the ‘large previous bushes’ within the title of this publish.

And it’s these these large, and due to this fact previous, bushes that I wish to talk about for the rest of this publish following the publication of an attention-grabbing paper on the subject by Oliver Visick and Francis Ratnieks from the LASI group on the College of Sussex.

Preferences

Each observational and experimental research have proven that the honey bee preferentially chooses voids of ~40 litres with a small (~10 cm²), south-facing, entrance situated over ~5 metres above floor.

The observational research concerned discovering bushes containing bees (‘bee bushes’) and bodily measuring the traits of the hollowed out trunk or department.

The experimental research concerned providing swarms the selection between massive or small voids, or massive or small entrances or north or south going through (OK, you get it) … and figuring out which they like.

For instance, they select 40 litre voids as opposed to 10 or 100 litres. These experiments are mentioned in Honeybee Democracy by Thomas Seeley who performed the vast majority of these research.

Whether or not they’d want a 75 litre void 7.5 metres above floor with a 12.5 cm² entrance over one going through north of 37 litres, 2 metres up, with a a lot bigger entrance was not examined.

Bees can’t be too picky

Nest website selection is an inexact science.

It needs to be.

Nest website preferences in honey bees developed earlier than hives existed, or for that matter church towers, or our ancestors.

By which I imply Homo erectus, over 2 million years in the past, not your grandparents.

Pure voids both exist in caves or in bushes, and there are much more bushes than there are caves. Moreover, bushes are available all styles and sizes. Due to this fact there have to be flexibility within the selection that the bees make.

One factor the bees don’t care about is the form of the void.

Spherical, cylindrical, cuboid, pyramidal … no matter.

This once more is sensible. The void (or hole) within the tree outcomes from pure harm, akin to a department breaking off following by water ingress, or a woodpecker or a wide range of different causes that don’t create areas of a specific geometric form.

How large are bee bushes?

So how large does a tree must be to accommodate a honey bee nest?

Let’s make some assumptions .

Let’s assume that the void is a sphere . As well as, let’s additionally assume that the trunk of the tree must be at the very least 10 cm thick throughout the hole to create sufficient structural rigidity that the tree survives winter storms.

As an apart, do the bees select higher insulated cavities with thicker partitions? I’m undecided whether or not the scout bees might assess this (they usually’re those making the selection) however it will be attention-grabbing in the event that they did. Somebody wants to use for a analysis grant …

You after all know (and I Googled) that the diameter of a sphere might be calculated from it’s quantity utilizing the next equation:

ø = ∛(6 · V / π)

Due to this fact a 40 litre spherical void has a diameter of 42 cm.

Add 10 cm on either side (as described above) and you find yourself with a diameter a bit over 60 cm. A tree of this diameter would have a circumference of ~1.8 metres.

Ideally that’s at 5 metres above floor stage.

I’m a bit over 1.85 metres tall and my attain is sort of precisely the identical as my top. If my assumptions are appropriate, I’d simply be capable of attain across the trunk of a tree massive sufficient to accommodate this theoretical or modelled honey bee nest website.

That’s, if I might attain thrice my top above the bottom. At chest top (a lot simpler to measure) it will be larger nonetheless.

My assumptions most likely aren’t appropriate .

Cylinders not spheres

You’ll be able to consider the sphere as a modelled honey bee nest website. The biochemist Erwin Chargaff as soon as stated:

One of the insidious and nefarious properties of scientific fashions is their tendency to take over, and typically supplant, actuality.

And, as a result of I don’t need you to assume that honey bee nests are spherical, let’s evaluation our ideas of the popular form and measurement of voids in bushes, and the bushes that home them, utilizing some actual knowledge i.e. ‘actuality’.

Firstly, tree trunks – at a primary approximation – are cylinders. Due to this fact it’s most likely cheap to imagine that they might accommodate a cylindrical void extra simply than a spherical one. This could provide the benefit that, assuming the quantity of the void was ample (by being longer), the flanking wall thickness might be larger, offering extra structural rigidity.

That’s not actuality … that’s largely arm waving.

OK … is that this higher?

Thomas Seeley and Roger Morse (Seeley and Morse, 1978) measured 21 pure nest websites in bushes. The bulk have been in oaks (Quercus sp.). Listed here are a few related quotes from the paper:

All nest cavities have been vertically elongate and roughly cylindrical .

… and …

The imply cavity diameter, top and (top/diameter) ratio have been 22.7 cm, 156 cm and seven.2, respectively,

And, only for completeness, utilizing V = πr2h, a cavity with these dimensions would have a quantity of ~63 litres.

Wall thickness and trunk diameter

Sadly, concerning the solely factor that Seeley and Morse seem not to have recorded is the thickness of the partitions of the tree trunk surrounding the void, or the diameter of the trunk .

A relatively cursory late evening search of the literature turned up a Bee Tradition article on thermal effectivity which said that

… honey bees have thick walled (common 150mm) tree nests.

If you already know of a greater supply please add a remark beneath.

So, the place are we? The typical diameter of the void occupied by free-living honey bees within the Seeley and Morse research was ~23 cm, and we would anticipate that will be surrounded by partitions that have been ~15 cm thick.

Due to this fact, the diameter of the trunk could be ~53 cm, giving a girth (2πr) of 1.67 metres.

Right here endeth the geometry lesson .

Large bushes are previous bushes

Timber taper. They’re wider nearer the bottom. Due to this fact a tree with a girth of ~1.7 m on the top of the honey bee nest website would have a bigger circumference at chest top … which is the conventional top above floor that bushes are usually measured at .

It seems that there are forester’s calculations for how a lot larger the diameter is, associated to the Girard kind class and expressed by way of tree taper, however let’s assume an additional 30 cm.

Timber develop comparatively slowly. An oak with a girth of ~2 metres at chest top is most likely about 80 years previous (PDF).

And that’s a comparatively small and younger tree … for an oak.

The fantastically named Large Stomach Oak within the Savernake Forest has a girth of 11 metres and is considered ~1000 years previous. There are equally aged bushes – not simply oaks – a few of that are even bigger. The Monumental Timber web site catalogues a few of these behemoths.

Tree-huggers and citizen science

Bosky groves, coppices, copses, thickets and spinneys are unlikely to comprise bushes sufficiently old (or, extra particularly, large sufficient) to accommodate a free-living honey bee nest.

Greater is best.

Greater bushes imply probably bigger cavities or – way more vital – extra alternatives for cavities of the suitable measurement. A really previous, very massive tree can have misplaced extra limbs, been nested in by extra woodpeckers, attacked by extra fungi and so on. and so is more likely to provide extra potential nest websites for a homeless swarm.

The Monumental Timber web site is a citizen science venture. You’ll be able to register and add notable bushes. There are ~60,000 already listed (worldwide, I can’t discover a breakdown by nation) .

Nevertheless, a lot extra attention-grabbing is one other citizen science venture, the Historic Tree Stock (ATI; Nolan et al., 2020), as a result of:

• it lists ~190,000 notable – usually massive and/or previous – bushes within the UK
• a cautious survey of 1052 of those notable bushes confirmed that over 4% of those who had cavities have been occupied by bees (Visick and Ratnieks, 2023)

The ATI web site is hosted by the Woodland Belief. I couldn’t get the maps to show correctly on my typical browser (Vivaldi), but it surely labored wonderful with Safari. If at first you don’t succeed … .

Mighty oaks from little acorns develop

Most of the mightiest oaks have been most likely felled within the 18^th and 19^th Centuries throughout the increase in shipbuilding wanted to construct the Royal Navy and for the enlargement of the British Empire. The lack of these bushes was additionally dangerous information for barbastelle bats. Replacements planted will solely now be rising into substantial bushes.

Most of the bushes that survived the ravages of the shipbuilders have been within the decorative gardens of stately houses or deer parks. Consequently there’s a greater density of those ‘bushes of particular curiosity’ (TSI) within the ATI database in these landed estates. TSI’s are outlined as:

… previous bushes that normally exhibit veteran traits, akin to a hollowing trunk, crown retrenchment and the presence of saproxylic fungi

The ATI defines bushes as historical or veteran relying upon the quantity of those traits which might be current.

Visick and Ratnieks (2023) surveyed 1052 TSI’s within the south-east of England earlier than the onset of swarming recording proof of cavities and the presence of honey bees.

By surveying websites early within the 12 months there was much less leaf-cover, making the surveys a bit simpler, and it was probably that any bees had been in residence overwinter.

Of the 1052 surveyed, 481 (45%) had seen cavities and 21 contained honey bees (i.e. 2% of the full bushes, or 4.4% of these with cavities). Throughout the survey a further 15 ‘bee-containing bushes’ have been situated that have been not listed within the ATI. Two bushes contained two colonies.

Traits of the bushes … and the bees

Bees have been present in oak (Quercus), candy chestnut (Castanea), beech (Fagus), ash (Fraxinus), pine (Pinus) and lime (Tilia). Solely the candy chestnut contained extra colonies than anticipated (7% vs 2% general), presumably as a result of these bushes have been a number of the largest surveyed and ~75% of them contained cavities.

Of the 1052 bushes surveyed, 65% have been oak, 8% candy chestnut and seven% beech.

The TSI ‘bee bushes’ have been bigger (1.7 m diameter, so a girth of ~5.3 m and due to this fact most likely about 350 years previous ) than these not containing bees (~1.3 m diameter).

The clue was within the title of the publish … these are ‘large previous bushes’. 

The median cavity entrance top was 6.8 m (vary 0 to >18 m) however entrance compass orientation was apparently random.

The south east of England is densely populated and there are lots of beekeepers within the space. The landed property with the best density of TSI’s, and the most important quantity surveyed, was Hatchlands Park, a Nationwide Belief property close to Guilford in Surrey.

Inside 10 km of this location the Nationwide Bee Unit’s BeeBase data 412 different apiaries . My back-of-an-envelope calculations recommend that the managed hive density within the space is 4-6 hives / km².

These free-living bees are not an remoted inhabitants. Whether or not they’re really self-sustaining or – just like the Central European inhabitants studied by Patrick Kohl et al., (2022) – dependent upon an annual inflow of misplaced swarms, stays to be decided.

I’ve not checked the opposite areas surveyed however suspect – like different free-living populations – they’re all in areas containing quite a few managed colonies.

21 down … 66,979 to go

If in case you have a superb reminiscence you’ll do not forget that about 3,000 phrases in the past I estimated there is likely to be 67,000 free-living honey bee colonies within the UK.

Visick and Ratnieks have discovered 21 of them. Extra importantly, they’ve proven {that a} database of venerable previous bushes supplies a route by which important numbers of such colonies might be situated.

Assuming that 2% of the recognized TSI’s throughout the UK are ‘bee bushes’ then they might dwelling as many as 3,300 free-living colonies.

Nevertheless, the ATI database ‘solely’ lists 190,000 bushes whereas geospatial knowledge suggests there are about 3 billion bushes within the UK, although most are wholly unsuitable for bees.

We don’t know what number of TSI’s there are within the UK, although Nolan et al., (2022) means that the ATI database might solely record ~10% of the full in England. Assuming 2% occupancy by bees this may be ~40,000 free-living colonies.

There are tons extra historical and veteran bushes on the market to be discovered and recorded … and looked for bees.

Lastly, for these of us dwelling within the distant, colder, wetter extra northern areas within the UK (and by extrapolation comparable areas in Europe and North America) don’t assume that each one these ‘bee bushes’ are within the balmy south. Ann Chilcott (of the superb www.beelistener.co.uk) and Thomas Seeley (PDF) discovered free-living colonies in Cawdor Wooden in Scotland.

In the event you go down within the woods at the moment … you might be in for a pleasing shock.

In fact, at the moment there can be no bees about because it’s too rattling chilly.

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Notes

Going again briefly to my guesstimates of minimal ‘bee tree’ diameters … it’s value noting that solely 5% of the TSI’s that have been occupied by bees (see the graph above) had a diameter much less than 1 m. Nevertheless, these bushes are notable – being massive/previous – and so maybe not consultant. I’m certain that smaller bushes might be occupied by bees, however that enormous (and due to this fact previous) bushes are more likely to be ‘bee bushes’. It’s additionally value noting that the chances of darkish gray bars within the graph add as much as 105% !

There are different efforts being made to catalogue free-living colonies e.g. HoneyBeeWatch, that are actually exterior the scope of this publish. I needed to introduce the idea of historical and veteran bushes as potential houses for honey bees, to debate the current scientific proof and, hopefully, encourage you to seek out comparable bushes (and bees).

References

Carpenter, M.H., and Harpur, B.A. (2021) Genetic previous, current, and way forward for the honey bee (Apis mellifera) in america of America. Apidologie 52: 63–79 https://doi.org/10.1007/s13592-020-00836-4.

Carr, S.M. (2023) A number of mitogenomes point out Issues Fall Aside with Out of Africa or Asia hypotheses for the phylogeographic evolution of Honey Bees (Apis mellifera). Sci Rep 13: 9386 https://www.nature.com/articles/s41598-023-35937-4.

Kohl, P.L., Rutschmann, B., and Steffan-Dewenter, I. Inhabitants demography of feral honeybee colonies in central European forests. Royal Society Open Science 9: 220565 https://royalsocietypublishing.org/doi/10.1098/rsos.220565.

Nolan, V., Reader, T., Gilbert, F., and Atkinson, N. (2020) The Historic Tree Stock: a abstract of the outcomes of a 15 12 months citizen science venture recording historical, veteran and notable bushes throughout the UK. Biodivers Conserv 29: 3103–3129 https://doi.org/10.1007/s10531-020-02033-2.

Nolan, V., Gilbert, F., Reed, T., and Reader, T. (2022) Distribution fashions calibrated with impartial discipline knowledge predict two million historical and veteran bushes in England. Ecological Purposes 32: e2695 https://onlinelibrary.wiley.com/doi/abs/10.1002/eap.2695.

Seeley, T.D., and Morse, R.A. (1978) Nest website choice by the honey bee,Apis mellifera. Ins Soc 25: 323–337 https://doi.org/10.1007/BF02224297.

Visick, O.D., and Ratnieks, F.L.W. (2023) Historic, veteran and different listed bushes as nest websites for wild-living honey bee, Apis mellifera, colonies. J Insect Conserv https://doi.org/10.1007/s10841-023-00530-7.