Figure 3 Iridescence in the butterfly Morpho rhetenor. a, Real colour image of the blueiridescence from a M. rhetenor wing. b, Transmission electron micrograph (TEM) imagesshowing wing-scale cross-sections of M. rhetenor. c, TEM images of a wing-scalecross-section of the related species M. didius reveal its discretely configured multilayers.The high occupancy and high layer number of M. rhetenor in b creates an intensereflectivity that contrasts with the more diffusely coloured appearance of M. didius, inwhich an overlying second layer of scales effects strong diffraction4. Bars, a, 1 cm; b,1.8 mm; c, 1.3 mm.