Bent posture improves the protective value of bird dropping masquerading by caterpillars (#323)
Masquerade describes a defence by animals that have evolved to closely resemble inedible objects such as twigs, stones, or bird droppings. Animals that masquerade often match their models in size or shape, and may even adopt specific postures in order to enhance their resemblance, causing predators to misclassify them as their model objects. The caterpillars of some moth species resemble bird droppings, and bend their bodies while resting on branches or leaves. We hypothesised that such bending might enhance the caterpillars’ resemblance to real bird droppings. In this study, we test this hypothesis by pinning artificial caterpillars with green or bird dropping coloration onto tree branches in both straight and bent postures, after which we exposed them to bird predation in the wild. We found that the adoption of a bent posture resulted in lower attack rate of birds on the artificial caterpillars with the bird dropping coloration, while green caterpillars experienced no benefit from the same treatment. This study is the first experimental demonstration of the protective value of a specific posture in masquerading prey, and highlights the importance of considering an organism’s shape and posture in the study of masquerade.