the spiraling flights of moths appear haphazard only because the mechanisms of olfactory tracking are so different from our own. using binocular vision, we judge the location of an object by comparing the images from two eyes and tracking directly toward the stimulus. but for species relying on the sense of smell, the organism compares points in space, moves in the direction of the greater concentration, then compares two more points successively, moving in zigzags toward the source. using olfactory navigation the moth detects currents of scent in the air and, by small increments, discovers how to move upstream.

barbara kingsolver