Spider’s Sight Is a Cornucopia of Color

PITTSBURGH—They’re about a half-centimeter long and have superb visual acuity. They can also see in full color through the use of a red filter in their two primary eyes, says a new paper out of the University of Pittsburgh on the Habronattus pyrrithrix jumping spider.

“The eyes of jumping spiders could not be more different from those of butterflies or birds, and yet all three tune their color sensitivities using pigments that filter light,” says Nathan Morehouse, assistant professor of biological sciences, within Pitt’s Kenneth P. Dietrich School of Arts and Sciences. “It's actually a pretty clever, simple solution with a big payoff.”

The payoff, for the male of the species, is that he gets to mate. Gentlemen Habronattus are quite colorful and use their vibrant appearance to attract a female. Scientists knew that some Habronattus pyrrithrix could see green and ultraviolet (UV) light through two of their eight eyes. It was assumed that they could also see reds and oranges—what would be the evolutionary benefit for males having red and orange coloration otherwise? But scientists had yet to figure out how the spiders could see ruby hues.

In his recent study, Morehouse and colleagues found that the arachnids have red filters that sit in front of cells in their eyes that normally detect green light. The effect is similar to the gels placed in front of theater lights to get different colors on a stage.

The paper on this “spectral filtering” that the researchers discovered was published in the May 18 edition of the Cell Press journal, Current Biology. It had never before been described in any spider, although similar strategies are known in birds, butterflies, and mantis shrimp. That makes this visual strategy a remarkable example of evolutionary convergence.

They may have “true” color vision, but that's not to say the spiders see the world in quite the way we do. The similarity lies in the fact that both this spider and humans have three color channels: jumping spiders have ultraviolet, green, and red channels, whereas people have blue, green, and red channels. The difference is that humans have three different, distinct color receptors rather than making use of a filter to perceive certain hues. “One fascinating thing about the trichromatic area in these spiders' retinas is that it is very restricted in field of view, which means they'd have to scan scenes ‘line by line’ to accumulate color information,” says Daniel Zurek, a postdoctoral researcher in Morehouse’s lab.

With the new findings in hand, the researchers say they are about to go spider hunting in Arizona in search of other species in this diverse Habronattus group. They hope to explore the role that color vision may have played in generating the diversity of these spiders over evolutionary time.

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