One adorable species of spider has a curious lack of vision. Experiments show that a jumping spider called Saitis barbipes has no ability to see red.
The male of S. barbipes is bright red, like many jumping spiders.
These red markings crown his head and extend along the two of his rear legs, which are used for threat displays.
David Outomuro of the University of Pittsburgh says they assumed they were using color for communication.
If the spiders can't see the red color, it makes the markings and their placement a mystery.
The researchers used 30 male and 7 female S. barbipes spiders to conduct their study. The spiders were killed with carbon dioxide and their eyes were removed so that the researchers could look at them.
The barbipes have a display. Oscar Mendez is an iNaturalist.
There was no sign of a red photoreceptor in the spider's retina, despite the team using microspectrophotometry. There was no sign of filters that would shift green photoreceptors to red.
It seems that what we see as red merely looks like an extension of their black markings. The patches of ultraviolet are different from the patches of red.
Males and females have different colors on their forward-facing body surfaces, which they display during their courting dances. Cynthia Tedore, a Biologist at the University of Hamburg in Germany, says that the red color must play a role in mate attraction.
We found that if red is perceived as different from black, it is perceived as a dark'spider green' rather than red.
Communication is just one of the many purposes that animals can use their color for. Camouflage to stay hidden or threatening to warn the predator off are examples of interaction with the predator.
How S. barbipes might look to itself and birds. Glenszczyk et al.,Sci. Nat., 2022.
The latter might be possible according to the team's research. They found that the red patches on the spider's body could be seen by birds and lizards, but that the black markings on the spider's body could be seen by other animals. There would be less contrast against a brown background with such markings together.
Future work should try to figure out why S. barbipes is so special. The research shows how we might need to think about differences in animal vision when designing our own world.
Nathan Morehouse of the University of Cincinnati asked, "What does a wind turbine look like to a bird that might run into it?"
We need to think about their perceptual worlds. I think it's fascinating to imagine how animals experience the world in a way that is completely alien to us.
The team's research has been published.
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