Scientists solve the mystery of why tarantulas are blue

Scientists at Yale-NUS College and Carnegie Mellon University (CMU) have discovered that tarantulas can see colors, which provides brand new insight into why the giant spiders are often bright blue or green.

The experts report that tarantulas are not as color-blind as previously thought, as their findings suggest that the spiders can perceive the bright blue colors on potential mates. While the blue colors on tarantulas are likely used for signaling mates, the researchers theorize that the green colors are used as a camouflage.

“While the precise function of blueness remains unclear, our results suggest that tarantulas may be able to see these blue displays, so mate choice is a likely potential explanation,” said study co-lead author Dr. Saoirse Foley.

“We have set an impetus for future projects to include a behavioural element to fully explore these hypotheses, and it is very exciting to consider how further studies will build upon our results.”

The researchers studied the expression of various proteins known as opsins, which are usually found in the eyes of animals. They found that most tarantulas have almost the same range of opsins that are expressed in spiders that have good color vision, such as the Peacock Spider.

The team used phylogenetic analyses to  reconstruct the colors of 110 million-year-old tarantula ancestors and determined that they were most likely blue. The study revealed that the evolution of green coloration appears to depend on whether the spider is tree-dwelling, which means that the color functions as a camouflage.

The research also showed that the blue coloration of tarantulas has been lost more frequently than it has been gained. On the other hand, the green coloration has evolved a few times but has never been lost.

“Our finding that blueness was lost multiple times in the New World, while regained in the Old, is very intriguing. This leaves several fascinating avenues for future research, when considering how the ecological pressures in the New and the Old Worlds vary,” said study co-lead author Dr. Vinod Kumar Saranathan. 

“For instance, one hypothesis would be differences in the light environments of the habitats between the New and the Old World, which can affect how these colours might be perceived, if indeed they can be, as our results suggest.”

The study is published in the journal Proceedings of the Royal Society B.

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By Chrissy Sexton, Earth.com Staff Writer