Jumping spiders actively pursue their prey, often jumping relatively long distances in order to catch them. Such feats require accurate depth perception. Nagata et al. (p. 469; see the Perspective by Herberstein and Kemp) show that jumping spiders use a process called image defocus, which allows depth perception to be obtained through the comparison of a nonfocused image to a focused image within the same eye. A single layer within the spider's eye that could not focus green light nevertheless contained a green sensitive pigment. Thus, this layer always receives an unfocused image, while other layers receive images in focus. Confirming this eye arrangement's role in depth perception, spiders unlucky enough to be bathed in green light nearly always jumped short of their target.
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