Imaging polarimetry of the circularly polarizing cuticle of scarab beetles (Coleoptera: Rutelidae, Cetoniidae).

The light reflected from the metallic-shiny regions of the cuticle of certain beetles belonging to the Scarabaeoidea is known since 1911 to be left-handed circularly polarized. Only photographs of a few selected species of scarabs, taken through left- and right-circular polarizers, have earlier been published. Through a right-circular polarizer these beetles appear more or less dark. This demonstration is, however, inadequate to quantitatively investigate the spatial distribution and the wavelength dependency of the circular polarization of light reflected from the scarab cuticle. In order to overcome this problem, we have developed a portable, rotating analyzer, linear/circular, digital, and imaging polarimeter. We describe here our polarimetric technique and present for the first time the linear and circular polarization patterns of the scarab species Chrysophora chrysochlora, Plusiotis resplendens (Rutelidae), and Cetonischema jousselini (Cetoniidae) in the red (650 nm), green (550 nm), and blue (450 nm) parts of the spectrum. We found the wavelength- and species-dependent circular polarization patterns in scarabs to be of a rather complex nature. These patterns are worthy of further studies.