Discovery of ordered and quasi-ordered photonic crystal structures in the scales of the beetle Eupholus magnificus.

The outer wing casings (elytra) of the weevil Eupholus magnificus are marked by yellow and blue bands. We have investigated the scales covering the elytra by using microspectrophotometry, imaging scatterometry, scanning electron microscopy and Fourier transform analysis. We demonstrate that the scales in the yellow elytral bands comprise highly ordered 3D photonic crystal structures, whereas the scales of the blue bands comprise quasi-ordered 3D photonic structures. Both systems, highly contrasting in their periodic order, create approximately angle-independent colour appearances in the far-field. The co-existence of these two contrasting forms of 3D structural order in the same single species is certainly uncommon in natural biological systems and has not been reported in the photonic literature.