The attractive iridescent green of the Indonesian Papilio palinurus butterfly is not generated by chemical pigments but by special concavities of 4-10 microns in diameter located in two-dimensional arrays in the wing scales. The optical image was captured by using an optical microscope (magnification 200) together with a digital pocket camera. Note that concavities act as secondary punctual light sources and the image is affected by the optical aberrations of the lens.
—Jose M. Medina, University of Minho, Portugal; and José A. Diaz, University of Granada, Spain
> Download hi-res image