Social Insects: Honeybee Dances
Honeybees provide humans with more than natural sweetener and sayings such as “busy as a bee” and “beeline.” They also provide a rare example of an animal communicating information about objects that are not close at hand. Some scientists say that honeybees, as simple as they are, provide the only example of such symbolic communication among nonhuman animals.
While most insects limit their social lives to a quick mating, bees and some of their relatives, as well as termites, form societies with division of labor and cooperation. Cooperation in most species requires some kind of communication, and the honeybee dance communication provides the archetypic example. A single worker bee (all workers are female, by the way) finding a rich source of nectar flies back to the hive. A short time later dozens of fellow workers make beelines to the nectar site.
How do the recruits find the site? That question has plagued naturalists since Aristotle. In the early 1900s, Austrian biologist Karl von Frisch began to study honeybees in earnest. At first it appeared to von Frisch that the bees merely sought out the odor inadvertently brought back to the hive by scout bees. But he also noted intense activity among returning bees and began watching closely. Those returning from his sugar-water feeding stations near the hive marched in a busy circle on the comb. Those carrying pollen from distant flowers danced a figure eight.
Von Frisch first called these behaviors the nectar dance and the pollen dance. But on further study, he formed a new ideathat the busy activity of scout bees after returning to the hive communicated more than merely excitement or information about food type. By moving his feeding station farther and farther from the hive, he determined that when the station reached 50 to 100 yards from the hive, nectar gatherers began dancing the figure eight pollen dance. This dance, von Frisch concluded, related to distant food sources, not to food type.
The bees bustled around in a purposeful manner, buzzing their wings and waggling their abdomens. They would hootchy kootchy in a straight line, then circle back to the beginningfirst circling left, then right. Von Frisch observed that the speed of the waggle and the angle of the line communicated both distance and direction to workers crowding around the scout.
On a horizontal hive, a bee can merely crosscut her circle in the direction of the flowers she found so full of nectar. The speed of her waggle and the number of circuits per minute indicate distance from the hive. But most bee hives consist of vertical combs. How then does a scout point out the right direction? Instead of indicating direction from the hive, she indicates an angle from the location of the sun. Forty five degrees to the right of vertical means forty five degrees to the right of the sun. Scout bees even manage to account for the apparent movement of the sun throughout the day. One thing bees cannot account for, however, is reorientation of their hive. Bees normally nest in trees, so it makes no evolutionary sense for them to evolve the ability to account for a rotated hive. But bee researchers can easily rotate a hive in a box so that it opens in a different direction. In that case, the bees become confused and cannot follow the direction information contained in the dance.
Suggesting, as von Frisch did, that bees have a “language” aroused the skepticism of some other scientists, who continue to this day to favor von Frisch’s earlier idea that scent alone guides bees. Nonetheless, von Frisch shared the 1973 Nobel Prize in Physiology or Medicine for his work.
A crucial test for any communication system is to experimentally modify it. Could a scientist communicate with the bees, using the dance to indicate the distance and direction of a target the bees had never visited? In 1989, a team of European scientists led by Axel Michelsen of Denmark's Odense University did just that. They built a bee of brass and beeswax with a bit of razor blade to represent the wings. Their robot bee could buzz its wings at the requisite 280 cycles per second (Hz), waggle its bottom and dance in a circle. It could even deliver drops of sugar water to the dance watchers.
Using a computer to control the robot, the researchers set their robobee to dancing, attempting to dissect the components of the dance. Dancing a normal waggle dance, this bee, like any robot, was a bit clumsy. But it got the message across. Some recruits used the information to fly to a target Michelsen had set up in a German field. On a different day, Michelsen sent the bees in the opposite direction. Bees found new targets regardless of wind direction, correctly following robobee’s message. Robobee could not have communicated with odor, because it never left the hive. Despite its clumsiness, Michelsen says “In our work with the robot bee, the dancer never visited any of the places advertised, and yet the bees turn up at the places indicated.” Years of researchsome using individually numbered beesand Michelsen’s robobee experiments have convinced all but a few bee scientists that the dance does indeed communicate distance and direction, just as von Frisch suggested.
But how do the bees perceive the dance? Hives are dark, so the workers crowing around a dancer cannot see. And Michelsen says research has shown it is unlikely that the bees can feel the hectic dance through their feet. Michelsen suspects the bees sense air currents set up by the scout bee’s wagging behind and buzzing wings. Robobee moves its wings and abdomen fast enough to mimic natural air currents. By modifying the dance, Michelsen highlighted the wagging portion of the dance as the key to conveying direction. The stereotyped semicircles, returning the bee to the starting point, may help to orient surrounding bees to where the next waggle will occur. Communicating distance proved more difficult for robobee. Michelsen thinks the robot lacked subtlety in conveying cues for distance, perhaps even giving conflicting information. Michelsen’s current research consists of digging deeper into how the air currents surrounding dancing bees convey information.
Other researchers have shown that only the small number of dance watchers who can keep their heads very close to the dancing bee get the message. Workers farther away must wait their turn to move in close and read the dance. And follow-up research has strengthened Michelsen’s supposition that the bees “hear” the air vibrations around the dancing bee, using their antennae. Without both antennae intact and functioning, dance watchers could not interpret the distance and direction information conveyed by the remarkable dance.