Figure 1.

(a) Butterfly wing scales. A key feature of all scales is the ridges running along their length. Several modified types of ridge are found to produce structural colour, these include: (b) a structure in which overlapping flanges running along the ridge, ‘ridge-lamellae’ (Ghiradella 1989), are exaggerated; (c) one in which flanges running perpendicular to the ridge-lamellae, called ‘microribs’ (Ghiradella 1989), are exaggerated; and (d) a variant in which a tilted multi-layer is formed by the microribs, and the ridge-lamellae are absent. Asterisk, ridge-lamellae; double asterisk, microribs. (Image of Callicore aegina courtesy of The Insect Company (www.insectcompany.com).)