Credit: Julie Johnson/Life Science Studios
UV coloration, which is invisible to the human eye, is used as a male courtship signal in orange sulphur butterflies, 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.