The male peacock spider (actually multiple species) is a flamboyant critter that seduces mates with an extravagant display and rainbow-colored behind. It is not particularly surprising, then, that color perception is a massive evolutionary advantage. In 2017, biologists confirmed that unlike the vast majority of arachnids, peacock spiders do indeed see in color.
Now scientists want to know: Does this ability to perceive color extend to their drabbier cousins, the wolf spider? The answer: yes, but only if it is green.
Unlike humans with trichromatic vision, wolf spiders have dichromatic vision. This means that while we can detect red, green, and blue light, these eight-legged creatures can only make out green and ultraviolet light.
George Uetz, a professor of biology at the University of Cincinnati, presented the research with his students at the American Arachnological Society meeting in June. His lab contains 1,200 or so wolf spiders, making it every arachnophobe's worst nightmare but the ideal setting to study spider behavior.
To test wolf spiders' perception of color, the team watched male and female spiders react to a video of a courting spider – a demonstration that usually involves a lot of tapping, bouncing, and twerking. The digitalization of the dance meant the researchers could adjust the color and intensity of both the background and the courting spider.
The female spiders were more forthcoming when there was a high contrast between the courting spider and the background. There was a better response when the video was fixed to monochrome or color, in comparison to the grayscale version. Interestingly, color was also important for the male spiders, the researchers said, who in this scenario are "eavesdroppers" – that is, amateur dancers attempting to learn and mimic the other male spiders' mating rituals.
"What we found is that for female spiders, intensity matters more than color," Uetz, said in a statement. "But for male eavesdroppers, color matters, too. That is the odd finding. We didn't expect that at all."
The ability to make out green as opposed to any other color serves an evolutionary purpose. Mating displays that take place in spring and summer will most likely take place with a green backdrop, and as the researchers found out, spider eyesight appears to change according to the season.
"That makes a lot of sense because when you go out in the early season when the spiders first come out, there are no leaves on the trees so there is broad spectrum light," Uetz explained. "But as the seasons change, leaves come out and everything turns green. Spiders have to be able to see the contrast against a lot of color backgrounds."
Now, here's a video of a wolf spider doing his best to attract a mate.