Stinging spines protect slug caterpillars (Limacodidae) from multiple generalist predators

Abstract

Predators have played a significant role in the evolution of herbivorous insects, and we can observe a wide variety of larval defense mechanisms in nature, especially among members of the Lepidoptera. Slug caterpillars (Limacodidae) are known for their unusual morphologies, including various types of protuberances and stinging spines on their dorsal surfaces, which suggest that their evolution has been strongly shaped by their interactions with predators. We tested the hypothesis that limacodid larvae with stinging spines would suffer less predation from generalist predators than larvae that either did not possess stinging spines or were more lightly spined. In a series of behavioral bioassays, we tested the preferences of 2 different invertebrate predators (assassin bugs and paper wasps) for “spined” or “unspined” larvae. We found that all of the predators preferred the unspined or lightly spined prey species over the heavily spined limacodid species Acharia (=Sibine) stimulea. Our results also indicate that at least one of the predators that we tested, the paper wasps, showed a form of aversion learning as indicated by a decreased number of inspections of A. stimulea after previous experience. We conclude that limacodid larvae that are heavily armored with stinging spines are well defended against attacks from invertebrate predators and are significantly more likely to survive predator encounters than are unspined or lightly spined larvae.