Glasswing butterflies (Greta oto) don’t really have wings made of glass, but you might think they do. Their wings are transparent, non-reflective, and non-refractive.
Most butterflies have colored scales on their wings, but glasswings have colors only on the wing fringes. Their wings are transparent because they don’t absorb or scatter much visible light. Transparent glass with a rough surface can refract or scatter the light in many directions causing it to be translucent. Light passes through, but you can’t see a clear image. The surface of smooth glass reflects some light in one direction such as when you see reflections on a computer or tablet screen.
The design of the glasswing butterfly’s wings avoids both refractive scattering and reflections. Examined under an electron microscope the surface of the wing shows tiny structures called nano-pillars that seem to be randomly arranged with random heights and widths. The radius of these pillars is smaller than the wavelength of visible light, so they don’t block light waves. It’s this surface structure which allows the wings not to refract or reflect light. The result is that looking through the wings is almost like looking through empty space.
Is there an evolutionary purpose for this? It makes glasswing butterflies slightly less visible to humans. However, their predators can see frequencies of light that humans can’t see. Glasswings probably get more protection from their predators by the toxicity they obtain from the flowers they feed on. Perhaps the most significant purpose of the transparent wings is the beauty which we think the Creator enjoys just as much as we do.
© Roland Earnst