A cobalt blue tarantula (Hapolpelma lividum).

Bastian Rast

Tarantulas are intimidating arachnids. From long, hairy legs to a propensity for nighttime escapades, they're definitely high on the list of "spiders you don't want to encounter in the middle of the night". But despite their reputation and creep factor, some tarantulas are more festive than expected – some are actually light blue and green.

In a new study published in Proceedings of the Royal Society B, scientists discovered that Hapolpelma lividum tarantulas – once considered color-blind – can actually perceive a certain amount of color. This doesn't necessarily mean that a tarantula could enjoy a rainbow, but it does have a significant impact on the hypothesis that these tarantulas develop such vivid colors to attract mates.

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Researchers from Yale-NUS College and Carnegie Mellon University have hypothesized that blue colors can be used to attract and communicate with potential mates, while the green color of some tarantulas can be used to camouflage and disguise tree species or tree dwellers.

The team looked at the physical expression of opsins, or light-sensitive proteins, in the eyes of tarantulas to see if they had full color perception, such as that normally found in spiders like the peacock spider (a notoriously brightly colored arachnid).

The results suggest that they may not have the full spectrum available to them, but that they can perceive the blue color that Hapolpelma lividum has developed. Using comparative phylogenetic analyzes, the scientists concluded that they were likely born blue for millions of years.

Saoirse Foley, Co-Lead Scientist at CMU, emphasized that while these conclusions are data-driven, there is still room for further confirmation. "While the exact function of the blue remains unclear, our results suggest that tarantulas may be able to see these blue indications, so partner choice is a possible possible explanation," she said.

"We have initiated future projects to include a behavioral element to fully explore these hypotheses, and it is very exciting to consider how further studies will build on our findings."


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