Structurally assisted blackness in butterfly scales

Abstract

Surfaces of low reflectance are ubiquitous in animate systems. They form essential components of the visual appearance of most living species and can explicitly influence other biological functions such as thermoregulation. The blackness associated with all opaque surfaces of low reflectivity has until now been attributed to strongly absorbing pigmentation alone. Our present study challenges this assumption, demonstrating that in addition to the requirement of absorbing pigmentation, complex nano–structures contribute to the low reflectance of certain natural surfaces. We describe preliminary findings of an investigation into the nature of the black regions observed on the dorsal wings of several Lepidoptera. Specifically, we quantify the optical absorption associated with black wing regions on the butterfly Papilio ulysses and find that the nano–structure of the wing scales of these regions contributes significantly to their black appearance.