Iridescence from diffraction structures in the wing scales of Callophrys rubi, the Green Hairstreak

The uniform green colour of the under surface of the wing of Callophrys rubi is due to the integrated effect of the iridescence from a mosaic of polygonal grains, 5.4 μm. diameter and 1 μm. thick. The ultrastructure of each grain is a simple cubic network, lattice parameter 0257 μm. The iridescent colour results from this structure acting as a volume diffraction grating giving a peak reflectance at about 0.548 μm., green, which is found to be close to the observed reflectance with a peak at 0.550 μm. measured by a spectrometer.