Multimodal warning signals for a multiple predator world

Anti-predatory defence: double jeopardy Toxic tiger moths are historically famous examples of warningly coloured insects; more recently it was found that ultrasonic sounds produced by these insects are associated with toxicity by bats and that non-toxic species can benefit from producing similar sounds. In a study of 26 moth species in southeastern Ontario, Canada, John Ratcliffe and Marie Nydam show that tiger moths' warning signals vary with the time of year, and therefore with the type of predator they are most likely to meet. Moth species that emerge in the spring, when birds are the biggest threat, tend to use visual signals such as bright colours to warn predators of their unpalatability. Species that emerge in summer rely more on ultrasonic clicks to ward-off echolocating bats, which pose the main threat during these later months. Similarly, species active during the day rely more on visual warning signals, and ultrasonic clicks are more useful at night. The research demonstrates how selection pressures from two distinct predators can guide the evolution of separate components of the insects' warning systems, resulting in a diverse arsenal of antipredator defences within the same species.