Beetle Scales: White and Light
The Cyphochilus beetle, which is native to South-East Asia, is whiter than paper, thanks to ultra-thin scales which cover its body. A new investigation of the optical properties of these scales has shown that they are able to scatter light more efficiently than any other biological tissue known, which is how they are able to achieve such a bright whiteness. The physical properties of such ultra-white scales on this and other species of beetle could be used to make whiter paper, plastics and paints, while using far less material than is used in current manufacturing methods.
Animals produce colors for several purposes, from camouflage to communication, to mating and thermoregulation. Bright colors are usually produced using pigments, which absorb certain wavelengths of light and reflect others, which our eyes then perceive as color.
To appear as white, however, a tissue needs to reflect all wavelengths of light with the same efficiency. The ultra-white Cyphochilus and L. Stigma beetles produce this coloration by exploiting the geometry of a dense complex network of chitin - a molecule similar in structure to cellulose, which is found throughout nature, including in the shells of molluscs, the exoskeletons of insects and the cell walls of fungi. The chitin filaments are just a few billionths of a meter thick, and on their own are not particularly good at reflecting light.
The research, a collaboration between the University of Cambridge and the European Laboratory for non-Linear Spectroscopy in Italy has shown that the beetles have optimised their internal structure in order to produce maximum white with minimum material, like a painter who needs to whiten a wall with a very small quantity of paint. This efficiency is particularly important for insects that fly, as it makes them lighter.
"Current technology is not able to produce a coating as white as these beetles can in such a thin layer," said Dr Silvia Vignolini of the University's Cavendish Laboratory, who led the research.
The findings will likely be relevant for many applications, enabling objects such as paper, plastics, paints, as well as white-light reflectors inside new-generation displays to be made whiter, while at the same time using a smaller amount of material.
et al.: Bright-White Beetle Scales Optimise Multiple Scattering of Light, Scientific Reports 4, 6075 (2014)