Dual structural color mechanisms in a scarab beetle.

The cuticle of a Mycterophallus cetoniine scarab species displays both red iridescence due to a multilayer reflector mechanism and rainbow iridescence due to a superimposed diffraction grating mechanism. This is the first reported example of an animal possessing two independent classes of structural colors arising from interference at the wavelengths of visible light. In this work, the Mycterophallus cuticle is characterized by light microscopy, spectrophotometry, scanning electron microscopy, and transmission electron microscopy. We compare the cuticle of the Mycterophallus species to two closely related Lomaptera scarab species, one with only a multilayer reflector and the second with only a diffraction grating. We calculate the correspondence between the nanostructural parameters and the optical properties of the Mycterophallus cuticle to determine the relative optical contributions of the two color mechanisms and the interactions between them.