Contact with caterpillar hairs triggers predator-specific defensive responses

Organisms have evolved morphological and behavioral traits that reduce their susceptibility to predation. However, few studies have considered how morphological structures work to provide informational inputs necessary for effective behavioral responses to predation risk. In this study, we demonstrate that the hairs of Orgyia leucostigma (Lymantriidae) caterpillars not only function as physical barriers that deter predators but also act to provide sensory inputs triggering behavior that reduces predation risk. In particular, the way in which caterpillars respond when their hairs are touched is predator specific. Mechanical parameters of the interaction determining the response were identified correlatively and confirmed manipulatively. Caterpillars predominantly dropped in response to high hair bending velocities and predominantly walked away in response to low hair bending velocities. These stimulus-specific responses appear to be adaptive as they led to increased survival. Our results demonstrate a functional link between morphology and behavior. The ability to respond effectively only after the initiation of a predator attack should reduce the costs associated with antipredator behaviors. Copyright 2011, Oxford University Press.