STRUCTURAL COLOUR: STAR SPECIES NUMBER 6
Special Power: The Whitest White!
Cyphochilus is a genus of beetles with unusually bright white scales that cover the whole exoskeleton. Cyphochilus beetles are native to Southeast Asia where they live amongst white fungi. The beetles are believed to have developed this white colouration as camouflage against predators.
The whiteness of the scales that cover the beetle’s wing cases is caused by a thin disordered photonic structure* (≈10 μm) which scatters light of all wavelengths with the same efficiency, thus resulting in a white colouration. This is particularly interesting as the beetle’s exoskeleton underneath the scales is black, meaning that the scattering must be very efficient in order to achieve such high opacity.
The white scales are composed of chitin, and are whiter than paper or any artificial material produced so far. The chitin filaments that make up the beetle’s scales are less than a micrometre thick – far thinner than a very fine sheet of paper. The chitin filaments are tightly packed to make a foamy structure, allowing them to scatter light efficiently. It has been proposed that the packing of this foamy structure is evolutionarily optimised to produce the brightest whiteness possible despite the low refractive index of chitin.
*A photonic structure is one that alters the wavelengths of lights (e.g. a prism).