Polarized-light navigation by insects.

T he eyes of insects are sensitive to a natural phenomenon that man is blind to: the polarized light of the daytime sky. It is this capacity that under­ lies the remarkable navigational ability of many insect species. Exactly how can an insect navigate by polarized light? To ask this question is really to raise three separate questions: What makes the visual cell of an insect sensitive to polarized light? How do some minimum number of visual cells coop­ erate to determine the direction of polariza­ tion at one point in the sky? How much information from how many points in the sky does the insect need for unambiguous navigation? The light radiated by the sun is unpolar­ ized, that is, its waves vibrate in all direc­ tions at right angles to the line of sight. In by RUdiger Wehner