News Spiders Jump With Deadly Accuracy in Green Light Spiders

January 26, 2012—Researchers have discovered a unique visual attribute that jumping spiders use in attacking and catching prey. The arachnids use what is called image defocus-proven in part by videos that show spiders jumping with deadly accuracy in green light (and fumbling in red).





We've long known that many insects have specialized eye capabilities, but Japanese researchers have now concluded that jumping spiders have a unique vision attribute.



Jumping spiders are able to stalk and rapidly pounce on their prey. To do this, they must gauge the distance the prey is from them.



Most animals gauge distance either by adjusting focal length of the lenses, as humans do, or moving their heads for an effect known as "motion parallax."



The new findings suggest jumping spiders have a third option, called image defocus.



The researchers, headed by Takashi Nagata, proved their theory by testing jumping spiders with only green light, in which they successfully pounced on their prey. But when only under red light , the spiders came up short.



In analyzing the jumping spiders' several layers in the retina of its primary eye, one of the layers contained a green-sensitive pigment, despite the fact that this layer does not focus green light. The researchers say because of chromatic aberration of the lens, the defocus is larger under red light. And under red light, the spiders incorrectly gauged the distance to the smaller insect.



Until now, no animals were known to use image defocus to determine the distance of an object.



Think of photos that are blurry in the foreground but clear in the background, and you can imagine how image defocus works.



The study findings were published in the AAAS journal, Science.



