Since 1999, I've been investigating the taxonomic distribution and possible functions of
diffraction gratings in nature. While these structures have been extensively studied in insects (H.E. Hinton; G. E. Ball), crustaceans (A. R. Parker), and reptiles (Gans and Baic 1977; Monroe and Monroe 1967), there is as yet no consensus regarding their utility to their bearers. Hinton argued that diffraction gratings in beetles act as a defensive visual signal, while Ball, Gans & Baic, and others have suggested that the grating microsculpture helps to shed soil and other clinging debris.
Regardless of their function, the recognition and diagnosis of diffraction-grating-based iridescence (as opposed to the metallic "iridescence" arising from multilayer reflectors) is critical for taxonomic descriptions and for understanding the evolution of coloration. Diffraction gratings create a distinctive "spectral" iridescence, with repeating, ordered spectra that will shift position on the body with respect to the angle of illumination.
For some examples of beetle diffraction gratings and their resultant iridescence, click here.
To marvel at how many posters and talks I've given on this topic, click here.
Got an insect (or other organism) with unusual iridescence? I'd love to hear about it.