Sometimes, bright colors on animals such as reptiles and insects are associated with venom and poison. In a recent study, scientists discovered why certain tarantulas (theraphosid) are a vibrant green or blue.
The collaborative study between Carnegie Mellon University (CMU) and Yale-NUS College has been recently published the Proceedings of the Royal Society B journal Biological Sciences. According to the team, it's a paradox for tarantulas to have a range of vivid colors despite nocturnal and crepuscular habits or active during twilight (dusk/dawn).
Their research indicates that blue and green coloration in the spider's setae or bristle-like structures "correlate with the presence of stridulation, urtication, and arboreality," the authors wrote. Stridulation refers to the behavior of producing sound by rubbing certain body parts together like how crickets make sounds.
Spider urtication refers to certain setae that may cause an inflammatory response if touched and is a separate function from spider venom. Arboreal species are specific arthropods found in temperate tropical climates.
Tarantulas Can See in Color
The team studied 37 types of tarantulas to analyze their vivid colors and eye functions. The scientists observed spider behavior as well as opsins or the light-sensitive proteins common in animal eyes.
They discovered, contrary to previous studies, that theraphosid can see in color and perceive the colors of other tarantulas. They believe that blue colors are associated with potential mates communicating while green colors are associated with camouflage.
Tarantula opsins also revealed that spiders active during the day have a full-color vision. The researchers also evaluated how the blue and green traits have been associated with the evolution of their species.
Determining the Role of Vivid Colors
Specifically, tarantulas can perceive the blue setae of other tarantulas. One of their ancestors from nearly 100 million years ago was found to be mostly blue. Moreover, the blue trait was not associated with common defense mechanisms meaning that the color is meant to attract potential mates and not scare off predators.
On the other hand, greenness depended on the tarantula's natural habitat. Blending into foliage was more important for tree-dwelling species compared to tarantulas living in other environments.
It was also interesting to see how green and blue traits have been lost and gained by tarantulas throughout their evolution. For example, blue coloration was lost several times while green coloration evolved but was never lost.
Dr. Vinod Kumar Saranathan from Yale-NUS College explained that species from Europe, Asia, and Africa regained blueness which was lost several times in the New World (Americas and Oceana). It may indicate that the different habitats and light environments in different regions may affect how the spiders perceive blue and green as their results suggested.
Dr. Saoirse Foley from CMU explained that the "precise function of blueness is unclear," but tarantula behavior suggests that the color is associated with choosing and communicating with a potential mate. She explained that the team has plans for further studies to confirm the roles of the tarantula's vivid colors.
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