Warning coloration is used by many prey species to advertise their unpalatability to potential predators and the evolution of such signals is strongly influenced by predator behaviour. I begin by reviewing the past literature on the potential role of invertebrates in shaping the evolution of warning signals in aposematism and mimicry. I then describe an investigation of the behaviour adult dragonflies in response to artificial prey of varying shape and colour, to determine the role of these traits in influencing foraging decisions. In two experiments, dragonfly species and sex, and prey size, influenced prey selection. However, neither prey colour, nor its interaction with prey size, affected the rate of attack of dragonflies. Through a feeding experiment, I also found that dragonflies preferred to feed on insects with softer exoskeletons. The implications of these findings for the evolution of warning signals and mimicry in small aerial insects are discussed.