“Blue is fascinating because the vast majority of animals are incapable of making it with pigments,” [Yale ornithologist Rick] Prum says.
In fact, of all Earth’s inhabitants with backbones, not one is known to harbor blue pigment. Even some of the most brilliantly blue things in nature — a peacock feather, or a blue eye, for example — don’t contain a single speck of blue pigment. So, how can they look so blue?
“They have evolved a new kind of optical technology, if you will, to create this color,” Prum explains — it’s a trick of structure.
Blue morpho butterflies are great examples. Biologist Dan Babbitt keeps some at the Smithsonian Museum of Natural History’s insect zoo.
The butterflies have a 6-inch wingspan — one side a dull brown and the other a vibrant, reflective blue. The butterflies have tiny transparent structures on the surface of their wings that bounce light in just the right way to make them appear a vibrant blue that’s so bright it almost hurts your eyes. But if you grind up the wings, the dust — robbed of its reflective prism structures — would just look gray or brown. […]
Structural color isn’t just a hack for making blue. It’s also a hack for lasting through time.
The best example might be a 50-million-year-old beetle carcass found in Germany in 1998, in a layer of dull brown and gray fossils. Even after millions of years underground, this particular beetle was still a brilliant, metallic blue.