Background/Question/Methods 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 amongst 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 undefended larvae. In a series of bioassays, we tested the preferences of a suite of invertebrate predators (assassin bugs, lacewing larvae and paper wasps) for defended or undefended larvae. For the paper wasps, we also examined the effects of previous experience on predation behavior. Results/Conclusions We found that all of the predators preferred the undefended or less-defended prey species over the well-defended Limacodid species Acharia stimulea. The paper wasps also showed some evidence of ‘avoidance learning.' Our results suggest that the stinging spines of slug caterpillars (Limacodidae) are highly deterrent to generalist predators and thus are effective morphological defenses. We conclude that Limacodid larvae with stinging spines are well defended against attacks from invertebrate predators and are significantly more likely to survive predator encounters than are undefended larvae.