How Jumping Spiders See in Color

Jumping spiders see in high-def. In relation to their tiny body size, these arachnids can see at a higher resolution any animal species, including humans. Now, a study published this week in Current Biology suggests their vision may be even more impressive. Researchers found that members of the jumping spider family can also see in three color channels. That means they have trichromatic or "true" color vision, just like humans.

Jumping spiders have four pairs of eyes that pick up on different visual cues. One pair is called "principle eyes", and can move their gaze and detect color and resolution. The other three pairs of so-called secondary eyes don't move and serve different functions like picking up peripheral signals and detecting motion. Until now, researchers only had evidence that these spiders could see two types of colors—green and ultraviolet (UV)—thanks to light-absorbing pigments in their primary eyes.

But looking at the spider’s lifestyle, that didn’t make sense. Seeing color, one might think, is important for these little arachnids. Many males sport flashes of bright color and dance to attract females. For example, here's the lengthy routine of a Habronattus pyrrithrix spider:

Habronattus pyrrithrix courtship

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During this dance the male reveals patches of hair of a variety of hues — greens, oranges, reds and so on--some of which the female would not be able to see with dichromatic vision. Why would a male be sporting a flashy crimson patch of fur if it's just going to look like a drabby bit of brown to a female? Both how the females see these colors and what they look like was a bit of an enigma, explains Jane J. Lee for National Geographic.

Intrigued by this conundrum, researchers decided to try to decode jumping spider vision. They recorded mating dances in the lab, dissected Habronattus pyrrithrix eyes, and measured the light wavelengths that their inner pigments absorbed. In addition to two pigments for green and UV light, they found a ruby red filter pigment, as well. This allows pigment cells that normall pick up greens to also pick up reds, oranges and yellows as well.

With red-hued sunglasses built into their eyes, they acheive their third color channel. In the mating dance, this allows females to discriminate between different colors at a further distance than if they only had two color channgels. Given the prevalence of coloration in other species, the team thinks that other jumping spiders of the Habronattus genus probably have "true" color vision, too.

Birds, reptiles and butterflies use similar filtering techniques to achieve their own additional color channels. "The eyes of jumping spiders could not be more different from those of butterflies or birds, and yet all three tune the color sensitivities using pigments that filter light. It's actually a pretty clever, simple solution with a big payoff," Nate Morehouse, a biologist at the University of Pittsburgh and a co-author on the stud, said in a statement.

Humans, in contrast, have three types of pigments that each absorb different wavelengths of light, spread out across the retina (the part of the eye that's senstive to light). In jumping spiders, the red filter is restricted to only part of the retina. "They'd have to scan scenes 'line by line' to accumulate color information," said Daniel Zurek, another biolgist and co-author in Morehouse's lab.

The color vision of a jumping spider might seem more limited in that sense. But, they have an entire channel to sense UV light that's entirely lacking in humans. So, technically, they can actually see more colors than humans can.

Helen Thompson | | READ MORE

Helen Thompson writes about science and culture for Smithsonian. She's previously written for NPR, National Geographic News, Nature and others.