Clicking caterpillars: Acoustic aposematism in Antheraea polyphemus and other Bombycoidea

Acoustic signals produced by caterpillars have been documented for over one hundred years, but in the majority of cases their significance is unknown. This study is the first to experimentally examine 'clicking' caterpillars from the superfamily Bombycoidea, with a focus on the silkmoth caterpillar, Antheraea polyphemus. Clicks produced by larvae measured on average 24.7 ms, displayed peak energy between 8 and 18 kHz, and varied in intensity between 58.1 and 78.8 dB peSPL. My hypothesis, that clicks function as acoustic aposematic signals, was supported by several lines of evidence. Experiments with forceps and chicks correlated sound production with attack. Sound production typically preceded or accompanied defensive regurgitation. Bioassays with invertebrates (ants) and vertebrates (mice) confirmed that the regurgitant is deterrent to would-be predators. Comparative evidence revealed that other Bombycoidea species, including Actias luna and Manduca sexta, also produce airborne sounds upon attack, and that these sounds precede or accompany regurgitation.