Figure 2.

Red scales with blue iridescence ofP. anchisesandP. lysander. A, B Whereas the scales of P. anchises are about flat, those of P. lysander are highly curved. C, D Scatterograms of the two differently-shaped scales. E Angle-dependent reflectance spectra of a wing piece of P. anchises measured with a two-fiber goniometric setup. The illumination angle (Δα) and detection angle (Δβ) were changed in steps of 5 degrees in opposite directions and symmetrically with respect to the angle of peak reflectance, which was at ~60° with respect to the normal to the wing plane. Inset: reflectance peak wavelength as a function of light incidence fitted with the interference condition for multilayers.