Golden Tortoise Beetle
The golden tortoise beetle, and some other species in its subfamily, is able to change colours due to an optical illusion. Just how this illusion could be produced was discovered in 2007 by researchers from University of Numar in Belgium, who studied the very similar gold-to-red colour change in the Panamanian tortoise beetle. Using scanning and transmission electron microscopes, they saw that the transparent shell of these beetles contains a three-tier structure, each tier made up of several tightly packed layers covered in patches of nanosized grooves. The tiers run from thickest at the bottom to thinnest at the top, and beneath them sits a layer of liquid red pigment. When the nanogrooves are filled with the red liquid, they give the layers a smooth surface, which perfectly reflects the light to give the Panamania tortoise beetle its metallic golden appearance. When the red fluid is drained from the grooves, in response to a stimulus such as agitation or copulation, it “destroys the optical properties” of the shell, leaving an “unobstructed view of the deeper-lying, pigmented red substrate”, the researchers reported in Physical Review E.