Coloration and Structure of Taiwanese Bronze Scarab (Anomala expansa)
Min-Nan Wu1, Chien-Yen Chen2, Wei Pan1, 吳敏男1*
1Physics, National Chung Cheng University, Chia-Yi, Taiwan
2Earth and Environmental Sciences, National Chung Cheng University, Chia-Yi, Taiwan
* presenting author:Wei Pan,
The structure and optical properties of the elytra of Taiwanese bronze scarabs (Anomala expansa) were investigated. The elytron is composed by a scale-like texture on the surface and a repeated bi-layers underneath. The reflectivity spectrum shows iridescence that the peaks shifts from yellow to green color regions as long as the incident angle (θ) increases. A shoulder peak at 600 nm (θ = 20°) is absent after gently scraping the surface, which indicates that the yellow color is contributed by the scale-like texture. The remaining peak at 550 nm (θ = 20°) in the spectrum resembles the simulated spectrum by assuming the refractive index of n = 1.54 and n = 1 for the adjacent bi-layered structure. This implies that the multi-layered structure contributes to the green coloration as well as the iridescent effect.

Keywords: iridescence , multi-layered diffraction, biomaterials