by Dave Goulson
Fully equipped, I would slice the bellies of the unfortunate animals open and carefully remove their innards, piece by piece. My mother had a copy of Gray’s Anatomy from her college days, and although it describes human anatomy, I used it to identify the various organs, many of which look surprisingly similar in small mammals and even in birds. I remember being struck by the fact that the kidneys of rats were exactly the size and colour of kidney beans. I would lay the organs out on the slabs of the garden path, and then puzzle over the pieces that I could not identify. I was never very good with spleens. I managed to get hold of some formaldehyde, and used it to pickle some of the more interesting body parts in jam jars, which I arranged on the shelves in my bedroom.
From dissection, it was a short but inevitable move to taxidermy. I have already mentioned that the Watkins & Doncaster catalogue contained a selection of tools and chemicals for taxidermy, including glass eyeballs of every possible size and colour. I now managed to get hold of a book which described how to do it – the wonderful Home Book of Taxidermy and Tanning by Gerald J. Grantz, which I still have to this day, the pages stained from various bits of animal innards. I saved up and bought the necessary chemicals and some taxidermy needles; curved along their length and of triangular cross section, they slide through the hide of an animal much more easily than a normal sewing needle.
Of course roadkills are rarely of much use for taxidermy: if the body is squashed, split and covered in tyre marks it is hard to reconstruct to a lifelike form. Getting hold of undamaged but dead creatures was something of an obstacle. My first specimen was a black-headed gull which I found on a day out to Ellesmere, a small and pretty town with a large lake and many waterfowl. Feeding bread to the ducks, I noticed one particular gull which was unable to fly and seemed quite sick, so I caught it, took it home and attempted to nurse it back to health. By dawn it was dead. Since it was unmarked, it seemed a perfect candidate for my first taxidermy attempt.
The principles of taxidermy are very simple. The body is sliced open in a neat line running from the bottom of the tail to the base of the neck. The skin is then peeled back and the carcass pulled out, turning the skin inside out. In a bird the wing bones and leg bones are chopped through, leaving the wings and feet attached to the skin. The neck has to be severed, leaving the bulk of the carcass free from the skin. The skin is then peeled forwards over the skull to the beak, carefully cutting around the eyes. The tissue, eyeballs, brains and other soft bits are then removed from the skull as best one can. In mammals, because there’s no beak attached, the skull can be completely removed and boiled in a pot – it is then much easier to get the brains out. The skin is treated with borax to preserve it, and left for a day or two. In the meantime, one has to construct a body out of wood wool (fine wood shavings) bound with lots of cotton thread. The animal’s carcass is used as a model, and as you might imagine it is important to get the shape as close to the original as possible. Three stiff wires (Mother’s cannibalised coat hangers) are then pushed through the body. One protrudes on either side, for attachment to the wing bones or forelegs. The second is sharply curved and pushed into the underside so that both ends point downwards, for attachment to the back legs. The final one is shorter, and is pushed into the top of the body where the neck would naturally attach; only one end is left protruding, on to which the skull is impaled. The skin is then rolled back over the skull, stretched over the new body, and the legs and wing bones attached to the appropriate wire with more cotton. The skin is sewn back up and voilà! One has a perfect replica of the original animal. Or at least that is the theory.
In practice, there were many problems. Professional taxidermists keep a range of eyeballs ready for use. I could not afford to do this, so I had to buy them after a suitable corpse had presented itself, and they often did not arrive until a few weeks later.6 Corpses don’t keep well (my mother wouldn’t let me put them in the freezer), so I had to stuff them without the eyes, then add the eyes some time afterwards. This is not ideal. Normally, the glass eyes should be placed in the skull before the skin is pulled back over it, but this was not possible, so I had to try push the eyes in through the eyelids from the outside once they arrived. By this time the skin had often hardened and shrunk a little, so the new eyes rarely sat comfortably; usually they were left protruding somewhat, giving my stuffed animals a startled expression, rather as if something had just been shoved up their bottom (which of course wasn’t far from the truth). Moreover, the rapidly shrinking skin would often not fit back over the new body, leaving a bit of a gap at the front from which wood shavings protruded. I eventually learned to compensate for this by making the wood-wool bodies smaller than the originals, but this gave my animals an emaciated appearance. I also found that it was surprisingly difficult to arrange the legs and wings in a pose that looked remotely lifelike. In my gull, the wings slanted upwards at an awkward angle, one leg was stubbornly turned sideways, and various feathers stuck up at unexpected angles. The overall effect was of a bird that had just received a large electric shock. Nonetheless I proudly took it in to my primary school class art exhibition. Dear Miss Scott remembers the gull to this day, although she must now be well into her eighties.
My efforts to stuff other animals were no more successful. I found a ferret dead in a snare, and deployed my limited skills once more. This time, the skin shrank so badly that I had to make the body incredibly narrow to stretch the skin around it. The poor creature ended up so thin it looked as if it was constructed from pipe cleaners. It also smelled spectacularly awful; live ferrets smell bad enough, but a dead one defies description. It was soon consigned to the garage, by order of my mum.
I came across a sickly wood pigeon which, miraculously, I managed to nurse back to some semblance of health by giving it dog worming tablets. After a couple of days of rest and recuperation in a cardboard box with plentiful hamster food to eat, it seemed quite chirpy, so I deemed it ready to return to the wild. With a bit of encouragement it took off from my bedroom window, but being somewhat weakened by its recent illness it crash-landed 100 yards away in the field opposite. I scampered outside and across the road but as I was climbing over the wall I saw that I was too late. The bad-tempered horse had trotted over and stamped on the pigeon with a front hoof, undoing my good works and leaving me with a slightly squashed corpse. Whilst the back end was badly damaged, the front, with its beautiful iridescent neck feathers, was fine. My solution was to mount the head and neck on a small shield-shaped piece of plywood, and hang it on the wall, rather like the heads of deer which are traditionally displayed as hunting trophies (but somewhat smaller and less impressive). The result of this new obsession was that my bedroom became more cluttered than ever, adorned now with a myriad of nightmarishly deformed creatures.
In the meantime, my fascination with insects had not abated. I became much better at rescuing forlorn bumblebees. I had noticed that it is not uncommon to see bumblebees, particularly queen bees in spring, walking slowly along the ground – particularly obvious when they are walking along pavement. I found that if I put my hand near them, they would feebly raise a middle leg, the defence posture of the tired bee; but that it was then possible gently to coax them up on to my hand and that they never stung. Having learned my lesson about warming them up using the cooker, I now tried a different approach and found that they would readily sip a mixture of honey and water in a teaspoon placed in front of them, and that after half an hour or so they would often revive and fly away (although sometimes they would climb into the teaspoon and become hopelessly wet and sticky). It was a few years before I came to understand exactly what was going on here, and it is quite revealing about the biology of bumblebees.
When I later went to secondary school, I loved biology lessons; it was, you will not be surprised to hear, my favourite subject. My biology teacher there was a short, rotund and enormously hairy man called Mr Newton (predictably known to us as Isaac) with a huge Sherlock Holmes-style pipe permanently clamped between his
teeth. Reeking of Clan, his favourite tobacco brand, he taught us that insects, fish, amphibians and reptiles are cold-blooded, while mammals and birds are warm-blooded. Now Isaac was an excellent if rather grumpy teacher, but he had got this wrong, although he had no way of knowing it. In fact, at almost exactly the time I was being taught this in 1976, an American scientist called Bernd Heinrich7 was making a name for himself by stabbing bees and hawkmoths. He was not stabbing them for fun, but rather to take their temperature. Measuring the temperature of a bee is quite tricky, as neither their mouth nor their bottom can accommodate a conventional thermometer. Instead, Heinrich used a thermocouple, a needle made from two thin wires of different metals welded together, attached to an electrical meter. As the temperature of the thermocouple varies, so the electrical conductivity of the junction between the metals changes. By stabbing the needle into a live bee, its temperature can be measured from the conductivity reading. Of course this isn’t much fun for the bee.
Heinrich developed a manic curiosity for spearing bumblebees and other large insects such as hawkmoths and dragonflies, and he found that these big, fast-flying insects are far from cold-blooded (his discovery coming at substantial cost to the local insect population). In fact, flying bumblebees have a body temperature that is generally well above that of the air around them, and tends to be constant at about 35°C, close to the usual temperature of a human body. An even rudimentary grasp of physics suggests that this is quite extraordinary. Keeping warm is harder the smaller you are. Big animals, such as blue whales, have a small surface relative to their volume, and so they cool very slowly and can keep warm even in very cold conditions (such as in the Antarctic Ocean). In contrast, small creatures, such as flies, have a vast surface area relative to their volume, and lose heat incredibly quickly. Yet bumblebees, which in the grand scheme of things are rather closer to flies than to blue whales, can keep themselves warm even when the surrounding air is 30°C cooler than their body temperature; a phenomenal feat. How do they do this?
Heinrich found that the answer is in two parts: keeping heat in, and generating it in the first place. Keeping warm is helped if you have insulation, and of course bumblebees have furry coats. Some bumblebees which live in the Arctic have particularly long fur, and they also tend to be bigger than more southerly bumblebees, which helps. The vital thing for a bumblebee is to keep its thorax (the middle section) warm, because this is where the flight muscles are; unless the thorax is warm enough, the muscles cannot contract sufficiently fast, and the bee cannot take off. The temperature of the abdomen (the hindmost section) doesn’t matter much in flight. The abdomen and thorax in a bumblebee are connected by a very narrow waist, and the front part of the abdomen contains a sac of air, so heat loss from the thorax to the abdomen is minimal (air is a poor conductor). Heinrich found that the abdomen in a flying bee could often be 15°C cooler than the thorax.
A furry coat and insulating air bags are a good start, but the heat has to come from somewhere, and it is generated by the contractions of the flight muscles. In flight a bumblebee flaps its wings 200 times per second (which equals 12,000 rpm), roughly equivalent to the speed of a high-revving motorbike engine. This generates a lot of heat, but of course comes at a cost: bumblebee flight is enormously expensive in terms of the energy that it uses. Many of the details have recently been worked out by Charles Ellington’s team at Cambridge University. They persuaded bumblebees to fly in a sealed wind tunnel, within which they were able to measure the bee’s oxygen usage and hence calculate its metabolic rate. Persuading a bee to fly in a sealed chamber is pretty tricky. Place her in a jar and she will take off and buzz up and down the side for a while, but it is not very much like natural flight. Creating wind using a fan in the chamber achieves very little; the bee either sits tight on the floor while the wind whistles past or she takes off but immediately crashes into the side of the chamber and falls to the bottom. Neither is very helpful. The secret to persuading her to fly for prolonged periods is to create a moving landscape that rushes past her as if she were flying along. This can be made by painting a pattern on to a loop of material stretched over a pair of motorised rollers. This contraption is then placed beneath the glass chamber. As the rollers turn, the landscape appears to move, which in combination with the wind convinces the bee that she is making good progress, even though she is actually going nowhere.
Using this set up, Ellington’s team could measure the amount of oxygen used up by each flying bee. This in turn enabled them to calculate how much energy bees burn in flight: an estimate of about 1.2 kJh-1. That figure may not mean a lot, so let me contextualise by saying that a running man uses up the calories in a Mars bar in about one hour. A man-sized bumblebee (which would, I admit, be pretty terrifying) would exhaust the same calories in less than thirty seconds. Hummingbirds are often thought of as having exceptionally high metabolic rates, but a bumblebee’s is roughly 75 per cent higher.
This simple fact explains an awful lot about the biology and conservation of bumblebees. They have to eat almost continually to keep warm; a bumblebee with a full stomach is only ever about forty minutes from starvation. If a bumblebee runs out of energy, she cannot fly, and if she cannot fly, she cannot get to flowers to get more food, so she is doomed – unless a small boy comes along and gives her a teaspoon of honey. With a stomach full of sugar she can start to fire up her flight muscles, shivering them to produce heat, and once she gets up to about 30°C, off she goes …
A bumblebee’s dense furry coat has obvious advantages, but it can create problems when the weather is warm. Bumblebees cannot help but produce lots of heat when they fly, which can be difficult to get rid of if the air temperature is also high. This is probably why bumblebees are not common in Mediterranean countries, and why there are almost none in the tropics. If their body temperature exceeds 44°C they will die; as they approach this lethal limit their metabolism collapses and they become unable to fly. It is noticeable that those species of bumblebee that occur in warmer climates tend to have shorter fur, while those from high latitudes and altitudes tend to be very large and very furry. Hence the huge size and long shaggy coat of the world’s largest bumblebee, Bombus dahlbomii, which inhabits the high Andes of South America.
Bumblebees do have a trick to help them lose heat in hot weather. As already mentioned, they normally keep their abdomen at a much lower temperature than their thorax, with the narrow waist connecting the two acting as a barrier. If the thorax starts to get too hot, the abdomen starts rhythmically to contract, sending surges of cool blood into the thorax and sucking back waves of hot blood. This heats the abdomen and so raises the surface area from which heat can be lost. Nonetheless, on very hot days in summer bumblebees will tend to stop foraging as noon approaches and recommence in the cool of evening.
Pumping heat from the thorax to the abdomen can also serve a very different purpose. The northernmost social insect in the world is a bumblebee known as Bombus polaris, which lives well within the Arctic Circle: large and unusually hairy, it can exist in regions where, even in the height of summer, air temperatures rarely exceed 5°C. Unlike other bumblebees, the Bombus polaris queens maintain a stable, high abdominal temperature (greater than 30°C) by pumping hot blood from their thorax to the abdomen. This enables them to develop eggs within their ovaries quickly, which is important in the very short Arctic summer. As the workers and males have no eggs to develop, their abdomens are substantially cooler.
The larger the bee, the easier it is for it to keep warm but the more prone it is to overheating in hot weather. This may explain why queen bees are so much larger than workers, for they are on the wing earlier, in the spring when the weather is cold. It may also explain why the worker bees that leave the nest to gather food tend to be larger, on average, than those that stay in the nest to look after the brood.
Moreover, bumblebees manage not only their own body temperatures, but also those of their brood and the nest. Dependent upon species, bumblebees have anywhere betwe
en two and seven months to complete their annual cycle. This would not be possible unless they speeded up the development of their offspring by keeping them warm, and as the grubs are flabby near-immobile creatures with very small muscles, they cannot warm themselves. Instead they are incubated by the queen (if they are the first batch of offspring), or by the workers. Once there are enough of them, the combined heat emanating from the workforce keeps the whole nest at a cosy 30°C or so without much difficulty. As with individual bees, overheating of the nest can be a problem in warm weather. If the nest becomes too warm, or if carbon dioxide levels climb too high, some workers will station themselves in the entrance and fan hot air out of the nest, acting like miniature air-conditioning units. Different bees have different temperature thresholds for beginning fanning behaviour; if the nest is slightly too hot, only one or two bees fan. If the temperature continues to rise, more and more join in. This very simple mechanism enables large nests to regulate their temperature very precisely, keeping it to within 1°C of 30°C day and night.
The ability of established bumblebee colonies to keep warm is most impressive. I once was looking for the kindest way to dispose of a colony of Turkish buff-tailed bumblebees – factory-reared bees which could not be released into the wild in the UK as they are not native here – and decided that freezing them was probably the best option. I placed the nest in its entirety in a domestic freezer at -30°C. The next day I came back to find the colony very much alive and buzzing loudly; the workers had gathered into a tight clump over the brood and were presumably shivering at maximum capacity. The queen was hidden in their centre, and seemed quite unperturbed.
