Sequential micro-Maltese cross array in the ground beetle Carabus insulicola

Abstract

The exoskeleton of the ground beetle Carabus insulicola was observed using polarizing optical microscopy (POM) with simultaneous transmitted and reflected light. The surface showed iridescence owing to the periodic microstructure. A Maltese cross array of the inner layer of the elytra was observed. The matrix of the middle layer of the elytra is composed of protein with the arrangement of a cholesteric liquid crystal (CLC)-like helical structure. The scanning electron microscopy observations revealed the layers structure of the exoskeleton of the ground beetle. Synchrotron X-ray diffraction measurement evaluated crystallinity of the exoskeleton. Morphology of the Maltese cross array of the beetle has similarity with synthetic chiral-CLC.

Keywords: Beetle; Maltese cross; Polarizing optical microscope; Scanning electron microscope.