Structural colour and photonic mechanisms in the blow flies

Structural colours in natural organisms are created by complex photonic architectures giving rise to remarkable visual appearances. In arthropods, these structures are usually made of biopolymers and comprise photonic crystals. They are often iridescent, i.e., their colours depend on the incidence and observation angles. Despite the interest of the scientific community in a large variety of species including those belonging to butterflies and beetles, some orders such as dipterans have been overlooked so far. In this work, the structural colours from the abdomens of two dipteran species, namely Calliphora vicina and Lucilia richardsi blow flies, with different displayed colours were investigated by spectrophotometry and optical simulations. Using electron microscopy, we identified multilayer photonic structures as the primary mechanism responsible for their visual appearances, with possible additional thin-film interference in C. vicina. In addition, the dipterans’ colours were analysed in terms of chromaticity as well as with respect to the visual sensitivities of the species and the ones of some of their predators. The reflectance spectra of the blow flies investigated were found to correlate with high absorption by their own and their predators’ photoreceptors. These findings indicate that structural colouration in blow flies may influence not only communication with conspecifics but also interactions with predators.