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Bee navigation: the eyes have it.

Bee navigation: The eyes have it

Entomologists have long known that bees use polarized sunlight to navigate. Two Swiss scientists now say that a bee's navigational "map" lies embedded in special photoreceptors in its eyes. According to Samuel Rossel and Rudiger Wehner of the University of Zurich, "... the array of receptors [in the bee's eyes] forms a template which the bee uses to scan and match the polarization patterns in the sky."

In the 1940s, Nobel laureate Karl von Frisch showed that bees have a simple yet elegant way of communicating the location of distant sources of food. When a foraging bee returns to the hive, she performs a "waggle dance" consisting of a short run ending in a loop that returns her to the beginning point of her run. The direction of her run indicates the direction of the food source with respect to the sun.

A sister bee observing this performance somehow remembers the size of the angle between the sun and the food indicated by the dancing bee. She flies out of the hive, makes a quick calculation of the position of the sun, and zips away at the same angle.

Bees have compound eyes made of almost 6,000 tiny lenses covering the openings of equally tiny tubes. Each tube contains eight light receptors that look like toothbrushes with the bristles facing each other at the lens end of the tube; the "handle" is the nerve going to the brane. The tubes located at the top of the bee's eye contain "toothbrushes" that specialize in detecting polarized ultraviolet light. Beginning at the back of the bee's compound eye and continuing around to the front, these specialized photoreceptors in each tube are arranged in a pattern that matches the direction of polarized sunlight.

Polarization results when the atmosphere scatters incoming sunlight and restricts the light's electrical field to a certain direction. When polarized sunlight enters a bee's eye, it stimulates the bristles, which in turn stimulate the photoreceptor "handles" that send a message to the bee's brain. Polarized sunlight with an electrical field direction that matches the direction of the bristles stimulates the bee's eye more than any other type of light.

In a complicated series of experiments described in the Sept. 11 NATURE, Rossel and Wehner showed that a bee flies in a circle until the special receptors in her eye detect the maximum stimulation from polarized light. The map in her eye tells her that, in this position, she is facing directly away from the sun. Remembering the orientation of her sister bee's waggle dance back at the hive, the bee veers off at the same angle to make a beeline for lunch.
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Title Annotation:photoreceptors in bee's eyes used to navigate
Author:Kleist, Trina
Publication:Science News
Date:Oct 4, 1986
Previous Article:Fiery probe of environmental problems.
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