Bumblebee electroreceptors

Water is a relatively good electrical conductor, and many aquatic and amphibious animals—including sharks, rays, catfish, and salamanders—are able to sense and respond to naturally occurring electric fields in order to detect food and threats. Duck-billed platypuses and spiny anteaters also share the faculty, known as electroreception, and use it underwater or in moist environments. (See the article by Joseph Bastian, Physics Today, February 1994, page 30 .) Only recently have researchers learned that cockroaches and bees can detect weak electric fields in dry, nonconductive air.

Daniel Robert and colleagues at the University of Bristol in the UK now report that the thread-like hairs that cover a bumblebee (dramatically on display in this close-up photo) provide a mechanism by which it senses weak electric fields. Hair motion is a recurring biological sensory motif, employed in the mammalian ear and used by insects and crustaceans to detect fluid flow. The Bristol team finds that bumblebee antennae and body hairs both respond to an applied electric field by rotating. The hairs, though, are more sensitive, move faster, and deflect by a greater angle. Moreover, only the hair motion is accompanied by a neural response. As bumblebees fly from flower to flower in the wild, they build up a net positive electric charge of some tens of picocoulombs; in the lab, even a fraction of that charge amplified the bees’ electromechanical response. (G. P. Sutton et al., Proc. Natl. Acad. Sci. USA, in press; photo courtesy of the University of Bristol.)

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