The natural world is resplendent with colour signals that are used by animals and plants to communicate. Most of these signals are matte in appearance, but there are also repeated instances where these signals appear glossy or shiny. The ability to produce a shiny colour signal results from dedicated and often highly complex features of a reflecting surface, which suggests that organisms go to some expense to engineer their appearance in this way. Precisely how shiny effects are achieved also differs between animals and plants, yet members of each group evidently strive for such effects. All of this suggests that shininess per se plays an important role in the various different ways that communication occurs. Compared to variation in other signalling features, for example colour, we however have a limited scientific understanding of the ultimate function of variation in signal shininess. This project therefore aims to explore and define the function of this important yet understudied dimension of visual communication in nature using butterflies as a model organism.