A Sting in the Tale (28 page)

CHAPTER SIXTEEN

A Charity Just for Bumblebees

If honey bees become extinct, human society will follow in four years.

Albert Einstein

Although this quote is oft-repeated, it is almost certain that Einstein did not actually say this. There is no record of when or where he said it, and I don't think he was prone to making sweeping statements on subjects in which he had no expertise. It is also almost certainly incorrect. It would undoubtedly be a disaster for some crops, and would put even more pressure on the global food supply which is steadily being stretched ever further by the growing human population. If the word ‘honey' was removed from this quote, it would be a little more plausible. In the UK, honeybees contribute at most one-third of all insect pollination, with much of the remainder provided by wild bees including bumblebees. If we were to lose all of our bees, then our diets would be much poorer, although most of us would survive. The major sources of carbohydrate that support the human population are cereals – rice, maize, wheat, barley, sorghum, millet and so on – and all of these are pollinated by the wind rather than by insects. On the other hand, almost every fruit or vegetable that is good to eat is pollinated by bees; imagine a diet without almonds, blueberries, raspberries, beans, apples, melons, cherries, cucumbers, pumpkins, and many more besides. Many vegetables such as potatoes or cabbage do not require pollination by bees to produce an edible crop, but nonetheless pollination is needed to produce the seed for next year. Even cows require pollination. You may think I'm getting a bit carried away here, but many fodder crops, such as clovers and alfalfa, require bees to pollinate them and so without bees we would have fewer livestock and hence less meat.

Bees aren't just important for the foodstuffs they provide to us. A myriad of other organisms depend on bees, including the wild plants that they pollinate, the animals that feed upon those plants, the worms and woodlice that help to decompose those plants, the bacteria and fungi in the soil around their roots, and so on. All of our natural ecosystems would be radically altered and much poorer without insect pollinators, and in the UK, the predominant pollinators are bumblebees.

I began studying bumblebees not because they are important pollinators but because they are fascinating, because they behave in interesting and mysterious ways, and because they are rather lovable. But as I became more familiar with what was known about them, it was made clear that they were in urgent need of help. I read Sladen's book
The Humble-bee
from 1912, and Alford's
Bumblebees
from 1975, which describe the biology of the UK's twenty-five bumblebee species,
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and it was soon apparent that many of the species that are described with familiarity in these books were now either extinct or had become exceedingly rare. The apple bumblebee,
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Cullem's bumblebee and the short-haired bumblebee had all gone extinct in Britain, and a further six species are on the UK ‘Biodiversity Action Plan' – often abbreviated to UK BAP – in recognition of their endangered status. Some of these are perilously close to extinction; the great yellow bumblebee, once found throughout the UK, is now found only in the far north and west of Scotland, while the shrill carder bumblebee, formerly widespread in the south of England and Wales, is now known from just seven populations. So it was that my interest shifted from focusing on understanding the foraging behaviour of bumblebees, to working on the ecology of the rare species, with a particular focus on understanding why they had declined and what we might do about it.

The first question that sprang to mind was why had some species gone extinct while others seemed to be surviving reasonably well? What was different about the great yellow bumblebee, or the short-haired bumblebee, compared to the buff-tailed or common carder? A common cause of rarity and susceptibility to environmental changes is specialism. Were the rare species more specialised, perhaps with regard to where they collected their food, compared to the common ones? Together with my students I spent a number of years studying the flowers used by different bumblebee species, both common and rare, across the UK. We spent a lot of time on Salisbury Plain because it was one of the few places where we could observe some of the rare species. We went to the Somerset Levels, to the marshes of north Kent, the sand dunes of south Wales, and the Western Isles of Scotland to find out what the rare bees that survived in these places were feeding upon.

To cut a long story short, the answer was clover. Most of the rare species seemed to be very fond of clover, particularly red clover, and other wild legumes such as tufted vetch and bird's-foot trefoil, probably because these plants provide pollen that is unusually rich in protein. Most legumes are meadow plants, the sorts of species that I am slowly encouraging in my field in France. Many also have deep flowers, matched by the long tongues that most rare bumblebee species possess. Three of the four longest-tongued species in the UK are extinct or nearly so: the great yellow, short-haired and ruderal bumblebees. Of the very long-tongued bees, only the garden bumblebee remains widespread. The rare species also tended to emerge later from hibernation; while buff-tails, white-tails and common carders emerge in March and April, the rare species tend not to emerge until June. Overall, it seems that the rare species are flower-rich meadow specialists, with long tongues to feed on deep meadow flowers and a predilection for protein-rich pollen from legumes. Their late emergence corresponds neatly with the onset of flowering of the first meadow plants, usually in June. In contrast, the common species tend to be short-tongued and unfussy as to what they feed on. They emerge early from hibernation and feed upon the spring flowers often found in deciduous woodland, and on the many flowers found in gardens. By doing so they are able to get a head start on the late-sleeping species. Once we had established that our rare bees were specialists on meadow flowers, it was immediately obvious why they had declined so badly; almost all of our flower-rich meadows have been destroyed by modern farming methods.

During our gathering of data on the ecology of the UK's rare bumblebees, another aspect of their decline became apparent. Intensification of farming had driven these species from the wider countryside, confining them to pockets of flower-rich habitat which survived, such as Salisbury Plain or the machair of the Hebrides. But then these isolated populations had often become extinct, even though the habitat within them remained largely unchanged. Wicken Fen in Cambridgeshire provides a nice example. Wicken Fen is a well-managed National Nature Reserve which in 1920 supported fourteen species of bumblebee (excluding cuckoos). By 1978 only seven remained. There is no great mystery as to why this happened. If you stand on the edge of Wicken Fen looking outwards, all you can see is flat, intensive arable land stretching monotonously to the horizon. The Fen itself still has flowers, but not enough to support viable populations of anything but the most resilient bumblebees.

Bumblebees are at a distinct disadvantage compared to most other creatures when it comes to surviving on small nature reserves. Most bumblebees are sterile – they are workers – with only the queens and males producing offspring. The number of breeding females is equal to the number of nests, and each nest requires quite a bit of good habitat to support it. As an illustration, suppose a successful nest requires 1 hectare of high-quality habitat – I haven't yet managed to work out the exact figure, which is probably much larger, but this will do for the sake of argument. In contrast, 1 hectare of meadow could easily support 1,000 meadow brown butterflies, with 500 breeding females. You may be wondering why this is important. The answer is that population size is critical for long-term survival. You may read that there are only 720 mountain gorillas surviving in the wild, or sixty Javan rhinos, and that they are therefore critically endangered. As a ball-park figure, conservationists agree that a population of less than fifty is probably beyond reprieve, doomed no matter what is done to help it. There are two reasons for this: firstly, a small population might go extinct through simple bad luck – a predator could eat them all, poachers might shoot them, or a disease or flood could wipe them out. Secondly, small populations suffer from inbreeding, whereby after a few generations all individuals become genetically related. I mentioned in Chapter 9 that most of us carry dud copies of some genes, but that we have two copies of each and so long as we have one good copy we are usually fine. Mating with relatives – who are likely to have the same duff genes as ourselves – risks having offspring with two dud copies of the same gene, and that is a recipe for disaster.
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This drop in offspring health is known as inbreeding depression, and can help to nudge an already vulnerable population towards extinction. Now most UK nature reserves are tiny, often only a few hectares, and so they are unlikely to be able to support more than a handful of nests of a rare bumblebee species, and a handful of nests does not constitute a viable population in the long term.

The pattern of extinction of the short-haired bumblebee illustrates this point. They were once widespread in southern England, but rapidly disappeared from most areas in the 1950s and 1960s as their habitat was swept away. By the 1970s only a half-dozen small populations remained, and one by one they went extinct. Dungeness National Nature Reserve was their last stronghold, but despite protection of the habitat at Dungeness, this last population faded away. It seems likely that such small, isolated populations were not big enough to be viable. If this is so, then are the remaining populations of the shrill carder and great yellow also heading steadily towards extinction, and if so, what can we do about it? It seems to me that we really need to get a handle on how small these populations are, and how much habitat is needed to support a viable population in the long term. It would also be really useful to know how far bees can travel between populations, for movement between populations helps to counter the negative effects of inbreeding by bringing in fresh blood at regular intervals.

To try to get answers to these questions, I started a programme of genetic studies of populations of rare and common bumblebees which continues to this day. We focused initially on two BAP species, the moss carder and shrill carder, and one scarce but widespread species, the heath bumblebee. Funded by the Leverhulme Trust, Ben Darvill headed north to Scotland and the Hebrides to collect samples whilst a new student named Jon Ellis travelled the length and breadth of England and Wales. Their basic aim was to sample DNA from bees and use genetic markers to identify how many nests were in each surviving population, whether populations were suffering from inbreeding, and over what distances bees moved between populations. The Hebrides served as a really neat island system in which it was very easy to quantify how isolated each population was, since bees don't live in the sea. I won't bore you with all the details, but three years later we had some fascinating insights into the population biology of these species. Most worryingly, estimates of the surviving population sizes were very low. Jon sampled all the seven known populations of shrill carder and estimated the number of nests in each population to vary from twenty-two to twenty-nine. There were no doubt some nests that he failed to detect, but nonetheless this suggested that these populations were teetering on the edge of extinction. Moreover, the rare species had very low genetic diversity, a sign of inbreeding, and they seemed to have poor dispersal abilities. The surviving populations of shrill carder had little or no gene flow between them, suggesting that they were too far apart for any bees to fly from one to another. In Scotland, Ben's studies showed that moss carders also had low mobility, rarely flying as far as 5 miles between islands, while in contrast the more widespread heath bumblebee seemed to be able to traverse 20 or more miles of open sea on a regular basis. It seems likely that one factor that makes a species susceptible to decline is a poor dispersal ability, for this renders populations more likely to become isolated from one another.

All of this work is ongoing; we continue to gather information on the ecology of bumblebees, all of which helps us to understand what needs to be done to help support strong, healthy populations in the long term. It is clear that we urgently need to create more suitable habitat in and around surviving populations of rare species such as the shrill carder, so that these populations can expand rather than drift to extinction. Ideally we need to try to link these populations by providing habitat stepping-stones. We know what habitats are needed, what flowers they should contain, and we have a pretty good idea how to create them. However, there is a problem. Knowing what to do is all very well, but knowledge does not in itself conserve any bees. Most scientific papers are read only by other scientists, and not by the politicians, farmers, gardeners or nature reserve wardens who might be able to do something with the knowledge that researchers unearth. After a long day in the field, a farmer does not come home, have his dinner, then put his feet up in front of the fire to read the latest edition of the
Journal of Animal Ecology
. It is hard to imagine him calling out to his wife, ‘Arrr, my luvver, avee zeen this article on dumbledores? Oyed better be zowin zum clover tomorrow.'
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Scientific articles are written to be understood by other scien-tists, and even then they often fail, for there are many papers that I struggle to make sense of. New methods of genetic analysis and statistics are constantly invented so it is very hard to keep up, and in any case over a million scientific articles are published every year, on average more than 150 on bumblebees alone. Even if a farmer or policy-maker had the time and background to make sense of these papers, he would be hard pushed to get hold of more than a small fraction of them, since most journals charge very substantial fees for access to their publications – even though the articles are written, reviewed and edited for free by scientists.