Dances in the dark
How Karl von Frisch discovered that honeybees give each other directions
On a warm summer afternoon, the entrance to a beehive is a scene of orderly traffic. Foragers drop out of the sky, loaded with pollen or with nectar in their stomachs, and vanish into the darkness. Inside, on the upright sheets of wax comb, some of them begin a curious routine: running forward in a short line, shaking from side to side, then looping back to begin again. Beekeepers had long noticed such behaviour, but they put it down to excitement after a successful trip. It was an Austrian zoologist, Karl von Frisch, who showed that these movements are a language, and that an insect whose brain is smaller than a grain of rice can tell its sisters where to find food.
Von Frisch was born in Vienna in 1886 into a family of distinguished academics. He began by studying medicine but soon moved to zoology, and his first discoveries concerned fish. Many scientists of the day assumed that fish were deaf. Von Frisch trained them to swim to a particular place for food whenever a whistle was blown, and so showed that they hear perfectly well.
Bees came next. The eminent zoologist Carl von Hess had argued that bees, like most invertebrates, could not see colour at all and that they visited flowers only because of their scent. Von Frisch set out to test the idea. He placed a dish of sugar water on a blue card among a number of grey cards of different shades, so that the bees could not find the food by judging brightness. When the dish was taken away, they still flew to the blue card. Further tests showed that they could also learn to recognise yellow, although red looked to them like dark grey.
It was during such experiments that he noticed something odd. Once a single bee had discovered the dish, many more arrived within minutes, as though she had told them where to go. To find out how, he built a hive with glass walls, so that the comb could be watched at any time, and marked individual bees with tiny dots of paint so that he could follow each one. He saw that a bee which had found food would return to the hive and dance, and that the bees which followed her soon appeared at the dish.
Von Frisch eventually distinguished two dances. A forager coming back from food close to the hive, perhaps within a hundred metres, runs in circles, which tells her audience only that something is nearby. If the source is farther away, she performs the waggle dance. She runs forward in a straight line, shaking her body from side to side, then circles back to the start, turning alternately left and right, so that her path traces a figure of eight. The waggle run carries two pieces of information. Inside the hive it is dark and the comb is upright, and the dancer treats the upward direction as the direction of the sun: her path is tilted away from the vertical by the same angle as the food lies to the left or right of the sun. The distance is shown by the duration of the waggle run, which grows longer as the source gets more remote.
There are complications. The sun does not stand still, and a dance describing its position at noon would be misleading by mid-afternoon. Von Frisch found that bees correct for this, so that a dancer goes on pointing to the same place hour after hour. When clouds hide the sun, they can still find their bearings from patterns in the polarised light of the sky, which humans cannot see. How bees measure distance proved harder to explain. In one experiment, bees were made to fly through a narrow tunnel with striped walls. They danced as if they had flown a very great distance, because the stripes seemed to rush past their eyes. Bees, it appears, judge how far they have travelled by how much scenery moves across their field of vision.
The dance takes place in darkness, so the audience cannot watch it as we might. Instead, the followers crowd round the dancer and keep their antennae in contact with her body, picking up the scent of the flowers she has visited and tasting the nectar she shares. The message also says how good the discovery is. A bee that has found a rich source repeats the waggle run many times, while one that has found a poor source soon stops dancing. In this way a colony of tens of thousands of bees directs its workers to the best food available, with no individual in charge.
Von Frisch announced his conclusions in the 1940s, and many biologists did not believe him. In the 1960s an American researcher argued that bees were guided to food by smell, not by the dance, and the argument lasted for years. It was settled by experiments that separated the dance from the scent. In the 1990s, researchers built a mechanical bee that could be made to perform the waggle dance, and found that real bees followed its instructions, though less reliably than those of a living dancer. In 2005, scientists in Britain and Germany attached tiny radar transponders to recruits and tracked their flights. The bees flew to the place that the dancer had indicated. Von Frisch shared the Nobel Prize in Physiology or Medicine in 1973, and few animals other than humans are known to communicate about a place they are not in.