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

Abstract

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.

Gold bugs and beyond: a review of iridescence and structural colour mechanisms in beetles (Coleoptera)

“…Circularly polarized light is also rare in nature; among insects, it has been documented only among scarabs and in the photic organs of certain lampyrid larvae (Hegedüs et al 2006b). In adult beetles, a circularly polarizing reflector is formed when birefringent chitin layers are deposited helically (i.e.…”

A nanostructural basis for gloss of avian eggshells

“…Iridescence can be produced by diffraction gratings, or when light passes through multiple semi-transparent materials that differ in refractive index, causing light to phase-shift and cancel out particular wavelengths at particular viewing angles [4,10,11]. Gloss, which is loosely defined as the specular or mirror-like component of light reflection, is a common component of animal coloration and is present in invertebrates, vertebrates and plants [2,[12][13][14]. Gloss is often produced by smooth or polished surfaces.…”

Navigation by light polarization in clear and turbid waters

“…Recently, several species were found to project and/ or detect circular polarization [9,10]. However, under water, circular polarization is mainly generated by internal reflection from the water surface and is found only at the margins of Snell's window [11].…”