Gold bugs and beyond: a review of iridescence and structural colour mechanisms in beetles (Coleoptera)

Members of the order Coleoptera are sometimes referred to as ‘living jewels’, in allusion to thestrikingly diverse array of iridescence mechanisms and optical effects that have arisen inbeetles. A number of novel and sophisticated reflectance mechanisms have been discovered inrecent years, including three-dimensional photonic crystals and quasi-ordered coherentscattering arrays. However, the literature on beetle structural coloration is often redundantand lacks synthesis, with little interchange between the entomological and optical researchcommunities. Here, an overview is provided for all iridescence mechanisms observed inColeoptera. Types of iridescence are illustrated and classified into three mechanistic groups:multilayer reflectors, three-dimensional photonic crystals and diffraction gratings. Taxonomicand phylogenetic distributions are provided, along with discussion of the putative functionsand evolutionary pathways by which iridescence has repeatedly arisen in beetles.