Despite its name the glass-winged butterfly (Greta oto) does not have wings made of glass, but the story behind their transparency is nonetheless fascinating.
The clear tissue that makes up the wings does not contain the colour-producing scales present in most butterfly wings. As a result, the tissue does not absorb or scatter much light, instead letting most of it pass through.
Not much light is reflected, either, due to microscopic structures on the surface called ‘nanopillars’. The nanopillars have a random distribution of sizes and positions, which means that there is a gradual transition between the refractive index of the wing and that of the surrounding air. This ensures very low reflection over a wide range of wavelengths.
The end result is that the wings appear optically transparent.