Coloration and Structure of the Wings of Chorinea sylphina Bates

The structure and the origin of transparency of the wings of Chorinea sylphina, a species of glasswinged butterflies, were explored using optical microscopy, scanning electron microscopy, UV photography, spectrophotometry, and optical polarimetry. We found that for normally incident light, the clear transparent areas of the forewings and hindwings exhibit significant transmission as well as minuscule reflection throughout the visible regime in the electromagnetic spectrum. We found that the transparency results from the sparsity, the semitransparency, and the upright orientation of single scales on the wing membrane. The red and dark brown colors of the nontransparent areas of the wings have a pigmentary origin. Coherent scattering from the slanted and overlapping lamellae in the scale ridges and diffraction from every scale's longitudinal network of parallel ridges are responsible for blue iridescence and shimmer at large viewing angles. The transparent areas of the wings function as absorbing linear polarizers, due to both the parallel ridges and the almost unidirectional orientation of individual scales on those areas.