Naturally grown nano-architectures found in living organisms are very sophisticated materials. Thanks to their interaction with light, these nano-structures produce amazing and original visual effects. The most remarkable phenomenon is the iridescence, which consists in colour changes with viewing angle.
First, in the cuticle of the Indonesian bug Calliphara sp., a periodic multilayer medium was observed. The specular reflection of light on this structure creates a metallic and an iridescent coloration from green to blue. Furthermore, this nano-architecture exhibits hygrochromic phenomena, i.e. the colour changes with humidity. Second, in the scales found on the elytra of the Brazilian weevil Entimus imperialis, three-dimensional photonic crystals were also observed. Each photonic crystal diffracts light independently. However, Entimus imperialis is one remarkable example of multi-scale structure creating "structural additive colours". The produced colour is indeed due to the interaction of light with structures having different sizes, nano-scale and micro-scale. In this case, some disorder in the structure scatters light in such a way that the reflectance is not affected by changes in the angle of viewing.