Abstract

Butterflies employ various optical principles for coloring their wings:
incoherent scattering, multilayer iridescence, and photonic crystals.
Nipple layers that act as anti-reflection coatings are present in the
wings of some butterfly species as well as in the corneal facet lenses
of many butterflies. Butterfly eyes are complex integrated optical
systems, with gradient index lenses, optical fibers, and selective
spectral filters that optimize vision. The eyes of moths and skippers
behave as metamaterial with a negative refractive index.