Mechanisms of Orientation and Pattern Recognition by Jumping Spiders (Salticidae)

Abstract

Jumping spiders capture flies by stalking them visually, and jumping when sufficiently close. They also distinguish prey from other jumping spiders. The first step in prey capture is for the spider to turn, using its four side eyes, to face the prey with its large movable principal eyes. It is shown that this turn can be made accurately in the absence of visual feedback by preventing the spider from turning its body, but allowing it to turn a cardboard ring instead. The angle through which the spider turns the ring is closely similar to the angle made by the stimulus and the body axis. Once a “side-eye” turn has been made the principal eyes normally observe the stimulus. These eyes have six muscles which can move the retinae up and down, side to side, and rotationally. Using anthophalmoscope techniquethe eye movements were observed while the spider watched stimuli. The eyes show spontaneous activity, tracking movements, saccades towards the stimulus, and scanning. During scanning the retinae fixate the stimulus with their central region, and move laterally back and forth across it at a frequency of 0.5 – 1 Hz. At the same time both retinae move conjugately through about 5e at a slower rate, 0.1 – 0.2 Hz. Previous authors had shown jumping spiders distinguish other spiders from prey by the positions and angles of the legs. It is suggested that scanning is a mechanism by which line detectors in the retinae are used to determine the inclination of contours present in a stationary stimulus.