Mueller matrix characterizations of circularly polarized reflections from golden scarab beetles.

Circularly polarized light (CPL) reflections are rare in nature. Only a few animal groups-most notably certain stomatopod crustaceans and certain beetles in the family Scarabaeidae-are known to reflect CPL from incident unpolarized light. Here, we examine five species of metallic scarabs in the genus Chrysina that, to the naked human eye, look remarkably similar. Using a spectropolarimetric reflectometer to characterize the complete Mueller matrix elements of the beetles' elytral surfaces, we found that four of the five species were strongly left-handed circularly polarized (LHCP), and only one scarab species, Chrysina resplendens, had an overall lower degree of polarization and switched from LHCP to right-handed circularly polarized reflectance depending on wavelength.