Colias Bab scales (IMAGE) George Washington University Caption UV coloration, which is invisible to the human eye, is used as a male courtship signal in orange sulphurbutterflies, shown here in magenta. Butterfly wings consist of two layers of microscopic scales, and in UV-iridescent butterflies, the upper layer harbors unique optical properties. These scales reflect ultraviolet thanks to complex layers of chitin on their surfaces, a nanostructure that resembles Christmas trees and is absent from non-UV scales. Credit Illustration by Julie Johnson/Life Science Studios Usage Restrictions With GW permission only. License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.