Lepidoptera (moths, butterflies, and caterpillars) are an uncommon cause of adverse reactions in humans. Most reactions to Lepidoptera are mild and self-limited; however, reactions in sensitive individuals and reactions to particular species can be severe and life threatening. Specific syndromes caused by Lepidoptera include erucism (cutaneous reactions from contact with caterpillars, moths, or cocoons), lepidopterism (systemic involvement), ophthalmia nodosa (ocular involvement), dendrolimiasis and pararamose (each with joint symptoms relating to a specific species of caterpillar), lonomism (a severe hemorrhagic disease related to Lonomia species), and seasonal ataxia (related to ingestion of Anaphe venata). In most cases, reactions to Lepidoptera can be treated symptomatically with prompt removal of offending hairs. Antipruritic or anesthetic topical preparations, topical steroids, and oral antihistamines are often used. In the case of potentially fatal Lonomia envenomation, an effective antivenin has been manufactured.