Fig. 7.

Angle-dependent spectra showing iridescence. a H. glaucippe. α = −15° indicates the angle of incidence where the UV-reflectance was maximal. Δα indicates the angle of incidence with respect to this direction of maximal reflectance. The UV-reflectance band shifts towards shorter wavelengths, as expected for a multilayer reflector. b C. regina. The blue reflectance band is maximal for an angle of incidence α = −35°. The dependence of the reflectance spectra on the angle of incidence is essentially identical to that of H. glaucippe. c Peak wavelength of the iridescence band as a function of angle of incidence, with negative angles signifying a tilt of the ridge multilayers towards the wing base. The values for H. glaucippe (orange circles) and C. regina (red squares) were derived from a and b. Similar measurements yielded the peak wavelengths for G. cleopatra (black left triangles, blue down triangles) and G. rhamni (green up triangles). The smooth curves are fits with the interference condition