Secret of a Bee's Odometer

Psychologists often use optical illusions to probe the workings of the human brain. Now a group of biophysicists has pulled the same trick on bees. By fooling the bees into thinking they've flown 30 times farther than they really have, the scientists settled an old debate about how bees judge distance. And in other bee news this week, a second group of researchers has developed a way to track bees by radar and watch as they learn how to navigate.

Bees keep close track of the distances they've traveled: When a bee returns to the hive after finding a particularly sweet source of nectar, it communicates the food's location to its apian audience by performing a "waggle dance." The duration of the dance is closely related to the distance the bee has traveled. Zoologists have argued for decades about whether bees measure distances visually or estimate them according to how much energy they expended on a flight.

To test how far a bee thinks it has flown, biologist Mandyan Srinivasan of the Australian National University in Canberra took advantage of a well-known illusion. At a given speed, travel seems slower if landmarks are far away--for instance, from cruising altitude, a plane doesn't seem to be flying as fast as it would if it were skimming a few feet above the ground. Srinivasan and his team trained bees--which normally fly about 2 meters above the ground--to fly through an 11-centimeter-wide tunnel that had a complex pattern of squares painted on the walls. The closer landmarks should trick the bee into thinking it is flying faster--and therefore farther in the same amount of time--than its accustomed distant landscape. The bees were fooled: Upon returning to the hive from their excursion down the 6-meter tube, the bees performed a waggle dance that lasted as long as a dance they would ordinarily do for a 200-meter flight, the researchers report in today's Science.

This is not the first evidence that bees use optical cues to judge distances: Animal behaviorist Harald Esch of the University of Notre Dame in Indiana showed in 1995 that bees underestimate distances when they fly from one tall building to another--just like passengers in a plane. But Esch agrees that Srinivasan's experiment is the most convincing proof yet. "This settles the issue of optical measurement of distance in honeybees," Esch says.

Another long-simmering debate in bee research is how accurately bees learn the directions to a food source from each others' waggle dances. Answering the question will require following an individual bee after it has seen a dance. But researchers can track bees by eye for only about 10 meters.

Now a group of researchers reports that they can track individual bees for up to 700 meters using a specially adapted form of radar that involves attaching antennas to the bees. According to entomologist Elizabeth Capaldi of the University of Illinois, Urbana-Champaign, the radar maps show that bees don't know how to "make a beeline" right away--they first need to take some training flights, in which they fly progressively longer distances at faster speeds, the researchers report in this week's Nature.

"It makes intuitive sense," says zoologist Fred Dyer of Michigan State University, East Lansing. Although some problems remain to be solved--such as making the long antennas small enough for the bee to enter the hive--both Dyer and Esch expect the radar technique to help decipher bee communication.

Posted in Environment