Ultraviolet Reflection of a Male Butterfly: Interference Color Caused by Thin-Layer Elaboration of Wing Scales

Males of the butterfly Eurema lisa, like many other members of the family Pieridae, reflect ultraviolet light. The color is structural rather than pigmentary, and originates from optical interference in a microscopic lamellar system associated with ridges on the outer scales of the wing. The dimensions and angular orientation of the lamellar system conform to predictions based on physical measurement of the spectral characteristics, including "color shifts" with varying angles of incidence, of the reflected ultraviolet light. The female lacks such scales and is consequently nonreflectant. The ultraviolet dimorphism supposedly serves as the basis for sexual recognition in courtship.