What Color are Purple Butterfly Wings: A Study of Optical Structures

At first glance, morpho butterfly wings appear to be a purple color. However, when they are held up to the light, they seem transparent. This is because morpho butterfly wings get their brilliant colors from the physical structure of the scales on the surface of the wing. This structure is a series of ridges spaced a few hundred nanometers apart. When light shines on these ridges, interference effects cause iridescence. We measured the spectrum of light reflected from a wing as a function of reflected angle and modeled these results mathematically. We also looked at morpho butterfly wings using a scanning electron microscope to verify the structure. Studying the structure of a butterfly wing can be used pedagogically to teach about the nature of light and to make observations about optical phenomena in the natural world