Many butterflies have brilliant colors, giant billboards that advertise their presence to potential mates. Color pattern and color constancy are important for mate recognition. Butterfly colors are produced by the pigments and fine structure of wing scales. The scales are outgrowths of the cuticle of the wing. The scales are modified hairs that can have complex structure that may enhance the color in a variety of ways. One swallowtail butterfly, Papilio nireus has bioluminescent scales that produce the beautiful green color on its wings.

A group of Chinese scientists* investigated of the fine structure of the green scales and found a complex structure behind the color production. They described the scales as consisting of several layers. On top is a network layer opposed to a photonic crystal (PC) layer (containing pigment), with both these layers separated from a lower “Bragg” (reflector) layer by an air space. The upper network…