Overnight perching aggregations of the aposematic Pipevine Swallowtail (Battus philenor: Lepidoptera: Papilionidae): implications for predation risk and warning signal use

Aposematic butterflies, those that are unpalatable and warningly colored, may aggregate during overnight perching to reduce the risk of predation. The conditions under which they aggregate and the postures assumed by perching butterflies may indicate how aggregations are a useful defense against predators, including the use of the warning signal. Additionally, studying these aggregations allows for a better understanding of the conditions under which their warning signal may be used. We investigated the overnight perching behavior of the aposematic Pipevine Swallowtail (Battus philenor) in both the field and in an enclosure. We found that the butterflies begin perching very close to sunset, when their blue iridescent warning coloration may still be effective, and the aggregations consist of between two and 21 individuals, which may accelerate warning signal learning by naïve predators. In both the field and enclosure, aggregated butterflies perched with the plane of their wings surfaces in parallel which suggests they perch in ways that increase the size of the warning signal. Additionally, B. philenor individuals perch in conspicuous locations which may facilitate warning signal detection, learning, and recognition. Our investigations of B. philenor aggregations lend support to the hypothesis that aposematic butterflies aggregate to increase the effectiveness of the warning signal against visually hunting predators.