Iridescence of beetles

Shiny beetle shells that look uniformly colored to the naked eye, like fly wings, also have fixed patterns that show up clearly when photographed under very diffused light.




The patches of colors are symmetrical even though the camera angle is not pointing perpendicular to the symmetry.




These two beetles (Tenebrionidae, Amarygmus sp.) found in different locations and different times have the same color patches which once again are symmetrical.

Iridescence is the third way to produce color from reflected light, the first two being conjugated double bonds (eg. pigments, dyes) and metal ions (minerals, gems). Iridescence in insects are largely caused by their shell structure that reflect light in ways such that the reflected light rays interfere constructively or destructively (or some combination in between) with each other. As different wavelengths experience different degrees of amplification or cancellation, different colors result, eg. if the blue wavelengths experience cancellation while red wavelengths experience amplification, red will result. There are apparently various ways this can be achieved, such as multilayer reflectors (eg. very thin layers of chitin) and photonic crystals.