Tarantulas: big, hairy, eight-legged, terrifying nightmares to some, adorable pets to others, blue.
Yes. Blue. Although most of the 900 or so species of tarantulas are varying shades of black or brown, the majority of sub-groups have at least one blue species. They are wonderfully named, too: the cobalt blue, the greenbottle blue, the Singapore blue, the Brazilian blue-green pinktoe, and plenty more. “Everywhere you look in the tarantula family tree, you can find examples of blue,” says Todd Blackledge form the University of Akron. “No, I didn’t realize either, and I work on spiders.”
Blackledge and his student Bor-Kai “Bill” Hsiung became interested in these unexpectedly colored spiders because blues are generally rare in the animal kingdom. Sure, there are peacocks, blue jays, morpho butterflies, and regal tangs, but it’s a relatively small list compared to the swollen ranks of animals that are red, yellow, green, or brown. As NPR once put it, “animals hacked the rainbow and got stumped on blue.”
Partly, that’s because it’s surprisingly hard to make blue pigments. Instead, most blue animals produce their colors using microscopic structures in their hairs, feathers, and scales. For example, if you zoom into the brilliant blue scales of a morpho-butterfly wing, you’ll see tiny layers, stacked on top of each other, and equally spaced. As light hits these stacks, some of it reflects off each layer. The distance between the layers is such that the blue portions of the reflected beams reinforce each other to produce intense bursts of colour.