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See Inside Scientific American Volume 306, Issue 4

What Is It?

Seeing green



Yukio Nanba/Minden Pictures

Scientists have long wondered how jumping spiders such as this one get visual information quickly and accurately enough to catch flies. In a study published in the journal Science in January, Takashi Nagata of Japan’s Osaka City University and his colleagues reported that jumping spiders compare focused and unfocused images to perceive depth—with a color twist. The investigators knew that the two innermost layers of a jumping spider’s two principal eyes (seen here as the two largest eyes) are tuned toward green light. But they focus that light differently: the deepest layer focuses green light clearly, and the second layer receives defocused images. To test whether differences in the two layers were important for depth perception, Nagata’s team shone green light on the spiders and tempted them with tasty flies. The spiders made spot-on jumps. Yet when the team bathed the prey in red light that did not contain green wavelengths, the spiders consistently missed their prey.

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