Read Online A Sting in the Tale by Dave Goulson - Free Book Online

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