Spiders are Deadliest When Seeing Green
Posted by LaraHeintz on Monday, Feb 06, 2012
Animals have evolved to have specialized vision, or other augmented systems (think bats and sonar) adapted to their hunting habits since the beginning of time, but now another variable that affects focal depth of field can be added to the list: color. And thanks to new research, arachnophobes are now surely stocking up on red light bulbs. Why? Because jumping spiders see best in green.
Jumping spiders, who trap prey by pouncing, have to very accurately gauge the distance of a pounce if they are to get a meal. Most animal species judge depth in different manners. Most vertebrates gauge depth through binocular or stereoscopic vision by having the brain calculate depth by receiving two different images from the eyes and amalgamating them together. Most insects, on the other hand, use called motion parallax , a depth cue controlled by how much an image travels across the retina.
The problem? A jumping spider doesn’t have binocular vision, and doesn’t seem to use motion parallax when hunting prey. However, a recent article published in Science, reports that jumping spiders have a unique method of focusing images, called defocus vision, a method of judging depth that is cued by the RGB spectrum.
The study, working with the species Hasarius adansoni, reported finding a “unique retina with four tiered photoreceptor layers, on each of which light of different wavelengths is focused by a lens with appreciable chromatic aberration.” The second deepest and deepest layers appear to have pigment sensitive to green light wavelengths, although only green light is focused in the last layer, while the visual imagery received in the second to last layer is blurry. Scientists working the study are proposing that jumping spiders then are able to gauge depth of field by processing the the difference between these two retinal layers which are cued by spectral wavelengths.
In simple terms, that means that jumping spiders might use the contrast between layers of different depths in their eyes to judge distance, rather than the horizontal differences between two individual eyeballs. It sounds almost like how autofocus works on a camera, but in this case it’s living (and, you know, a spider). Enjoy the National Geographic video on the research below, and remember the old adage: When a jumping spider’s afoot, don’t wear green. Or something like that.
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Grad Student in Media Studies with a penchant for pumpkin donuts, DIY electronics, and a nice cup of coffee.
