In a new study from the University of Cincinnati, researchers have discovered that a type of brightly colored jumping spider is color blind. The study was focused on Saitis barbipes, a common jumping spider found in Europe and North Africa.
The males of this species have a furry red crown and legs. They are known for performing elaborate courtship dances.
“We assumed they were using color for communication. But we didn’t know if their visual system even allowed them to see those colors,” said study co-first author David Outomuro.
Using microspectrophotometry to examine jumping spiders collected in Slovenia, the team found no evidence of a red photoreceptor. The experts also looked for colored filters that might shift green sensitivity to red, but found that there were none.
The researchers ultimately determined that, most likely, bright red colors appear no different than black markings to these jumping spiders.
“To quantify and visualize whether females may nevertheless be capable of discriminating red from black color patches, we take multispectral images of males and calculate photoreceptor excitations and color contrasts between color patches,” explained the study authors
“Red patches would be, at best, barely discriminable from black, and not discriminable from a low-luminance green.”
“It’s a bit of a head-scratcher, what’s going on here,” said study co-author Professor Nathan Morehouse. “We haven’t solved the mystery of what the red is doing.”
Even though animals use color in all sorts of ways, including camouflage, it’s not always apparent what bright colors might signify, according to Professor Morehouse. “We spent a lot of time talking about it as a group. What else could it be? I feel there’s an interesting story behind the mystery.”
Study senior author Cynthia Tedore, a research associate at the University of Hamburg, said the results of the research were surprising.
“Males have bold red and black coloration on their forward-facing body surfaces which they display during their courtship dances; whereas, females lack red coloration altogether. This initially suggested to us that the red color must play some role in mate attraction,” said Tedore.
“Instead, we found that red and black are perceived equivalently, or nearly so, by these spiders and that if red is perceived as different from black, it is perceived as a dark ‘spider green’ rather than red.”
The researchers believe that the spider’s red and black colors may possibly improve defensive camouflage.
“For predators with red vision, at natural viewing distances, the spider’s red and black color patches should blur together to become an intermediate orangish-brownish color, which would help the spider blend in with its leaf litter habitat better than all-black coloration would,” said Tedore.
The experts noted that there are many colorful jumping spiders that see red perfectly well. There are also many dull-colored spiders that have great color vision.
The study is published in the journal The Science of Nature.