Glasswing butterflies have transparent wings which allow them to hide from the world. Recent research shows that the wings are almost invisible due to their narrow bristle-like scales and waxy, glare cutting coating.
Flat scales tile the wings like shingles to give moths and butterflies their vivid colors. Very few species have clear wings. Nipam Patel is an evolutionary and developmental biologist from the Marine Biology Laboratory. He first examined the wings of many species together with his students in an embryology course. He says it was incredible because they discovered every possible way to have transparent wings, from having see-through scales to none at all.
The structural diversity and optical properties that make wing transparency transparent were previously explored using adult specimens in museums. This meant that the developmental processes behind transparency were not known. Patel and his collaborators raised glasswing butterflies, and recorded their wing development. This was the first time-series record of this process, and it is now published in the Journal of Experimental Biology. Their research shows that glasswing butterflies have narrow bristles to make clear patches and fewer scale precursor cells (top right).
Because colorless wings can shine, butterflies have developed ways to reduce reflected light. The researchers examined nanopillars with powerful electron microscopes. These tiny structures are believed to block glares from the surface of the glassy wings. The researchers discovered that nanopillars of chitin (a fibrous substance found within insect exoskeletons) are supported by a layer of nanopillars. However, this layer is covered with a layer of waxy chemicals that reduces the amount of reflected sunlight. These findings could lead to new antireflective materials, according to the researchers.
Robert Reed, Cornell University ecologist, said that the study sets the stage for future research to identify the genetic mechanisms through which color in butterflies and moths (or lack thereof) evolves. He was not involved in the study. Reed says that scales are an evolutionary innovation that marks butterflies and moths. It's therefore quite remarkable that some species have seen a reversion from color to color.
