Mystery deepens for what made tarantulas blue

Sexual display is probably not the answer

tarantula Chromatopelma cyaneopubescens

BLUE MYSTERY  Internal structures, not pigment, puts blue in hairs on the tarantula Chromatopelma cyaneopubescens. What drives the evolution of such color in animals that probably can’t see it still puzzles researchers.

Michael Kern/

Blue hair has evolved independently at least eight times among tarantulas, a new study finds. But the puzzle of what benefits the color might bring has gotten even more mystifying.

Lab measurements show unusually similar hues from species with very different color-causing structures inside the hairs, researchers report November 27 in Science Advances. That convergence dashes the idea that blue is just a side effect of some hair property like ability to shed water, says study coauthor Todd Blackledge of the University of Akron.

Spider specialists don’t expect that the coloring wows females, because the eyes of tarantulas probably can’t tell blue from other colors, Blackledge says. So now he wonders about protection from predators: What looks bright blue in the lab could go inconspicuously dull in the greenish light of tropical forests.   

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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