Structural optimization for broadband scattering in several ultra-thin white beetle scales

Recent work discovered the remarkable optical scattering properties of the scales of the white beetle Cyphochilus. It was suggested that its brilliant whiteness and brightness were due to optimization of the microstructure within its scales. Here we compare the microstructure of Cyphochilus scales to those of two other white beetles, Lepidiota stigma and Calothyrza margaritifera. Extensive optical modeling and experimental data suggest that each species displays structural optimization designed to maximize optical scatter. Optimization of the scale filling fraction is observed, as well as optimization of scattering center spacing and diameter. Cyphochilus, in particular, displays a high degree of structural optimization, resulting in its bright white appearance.