Some tarantulas have a characteristic that might be able to charm even the most dedicated arachnophobe: they're blue. A striking, shimmering blue. And now scientists have learned that many species of the spider have evolved the same blue hue independently -- at least eight different times.
The findings come from a study just been published in the journal Science Adventures by researchers from The University of Akron (UA) and the Scripps Institution of Oceanography at the University of California, San Diego.
The tarantulas create the blue look not from pigment but from nanostructures in their hairs.
And while other animals, such as birds and butterflies, also use such tiny structures to create the kinds of colors that will impress females, sexual selection doesn't seem to be the reason tarantulas evoloved the blue.
"Tarantulas don't see well, so their blue colors could not have evolved for courtship," said the study's lead author, UA biomimicry fellow Bor-Kai (Bill) Hsiung, in a statement.
What's more, the blue shade in the tarantula species is close to the same in all of them, and yet it's created with structures that aren't the same for each species.
"Even more remarkably," said Hsiung said, "different types of nanostructures all evolved to produce the same 'blue' across distant branches of the tarantula family tree. In other words, natural selection has led to convergent evolution."
One nagging question that persists, and is yet unanswered, is "why?" What evolutionary edge do the spiders get out of being blue, if not for mating? Is the striking coloration meant, for example, to scare away potential predators?
"For them to be this specific, it means that the blue color must itself have some function," Hsiung told The Atlantic. "We definitely think it has to have some kind of visual function."
For now, though, the scientists just can't be sure.
Meanwhile, increasing our knowledge about the nanostructures could be well worth the effort, Hsiung notes. Especially if the mechanisms could be reproduced.
"They could be used as pigment replacements in materials," the researcher said. "Such as plastics, metal, textiles and paper, and for producing color for wide-angle viewing systems in phones, televisions and other optical devices."