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

Area of Science:

• Biomimetics
• Materials Science
• Entomology

Background:

• Insect exoskeletons exhibit complex microstructures for optical properties.
• Iridescence in beetles is often linked to structural coloration.
• Understanding beetle exoskeleton structure can inspire synthetic materials.

Purpose of the Study:

• To investigate the microstructural basis of iridescence in the ground beetle Carabus insulicola.
• To characterize the structural organization of the beetle's exoskeleton layers.
• To compare the beetle's structural morphology with synthetic chiral liquid crystals.

Main Methods:

• Polarizing optical microscopy (POM) with transmitted and reflected light.
• Scanning electron microscopy (SEM) for layered structure analysis.
• Synchrotron X-ray diffraction for crystallinity evaluation.

Main Results:

• Observed iridescence due to periodic microstructure on the exoskeleton surface.
• Identified a Maltese cross array in the inner layer of the elytra.
• Revealed a cholesteric liquid crystal (CLC)-like helical structure in the protein matrix of the middle layer.
• SEM confirmed the layered exoskeleton structure.
• X-ray diffraction assessed exoskeleton crystallinity.

Conclusions:

• The exoskeleton's iridescence is attributed to its periodic microstructure.
• The beetle's elytra exhibit a CLC-like helical protein structure.
• The Maltese cross morphology in Carabus insulicola resembles synthetic chiral-CLC structures.
• Findings provide insights into natural structural coloration and biomimetic material design.