The wings bear coloured, easily dislodged scales which produce patterns on the wing surfaces. Sometimes iridescent or metallic colours may be produced by light diffraction in the wing structure. The main elements of the patterning are shown in Text Figs. 5 & 6, below. The males of many moths have various folds or grooves in the wings which are usually associated with specialised scales and pheromone-secreting glands.