Lepidopterism refers to the adverse medical effects of contact with insects of the order Lepidoptera, which includes both moths and butterflies. These effects typically result from contact with an insect during the caterpillar (larval) stage. Lepidopterism involves multiple pathologic mechanisms, including direct toxicity of venom and mechanical irritant effects. Clinical patterns associated with contact with lepidoptera include localized stinging reactions, papular urticaria and dermatitis, urticarial wheals, and hemorrhagic diathesis. Accurate diagnosis of symptoms associated with contact with caterpillars, butterflies, or moths is nearly impossible without a reliable history of exposure, as the histology of exposure is nonspecific. Treatment is largely empiric and should be based on symptoms. We report a case of lepidopterism in a patient with acute cutaneous lesions following exposure to an adult-stage black butterfly (Hylesia nigricans).