Moth wing scales. Coloured scanning electron micrograph (SEM) of scales (blue) on the wings of a common clothes moth (Tineola bisselliella). These delicate powdery scales are formed from tiny stacked modified hairs, or setae, made of chitin, a common substance in insect exoskeletons. The iridescence of the colours of a moth's wings is produced by the diffraction of light by the microscopic ridges on these scales.