Introduction: The asp caterpillar (Megalopyge opercularis) is endemic to the southeastern United States, with most sightings in Florida, Texas, and Louisiana. A few hundred caterpillar envenomations are reported annually with most cases occurring in July–November. Asp caterpillars have hollow spines along their backs that contain venom. Contact with these spines is what produces the characteristic “sting” resulting in contact dermatitis and a localized hypersensitivity reaction collectively referred to as lepidopterism. Symptoms of lepidopterism may include severe burning pain, pruritis, edema, nausea, vomiting, abdominal pain, and headache. Symptoms are often self limited, and treatment should focus on expedited removal of implanted spines and aggressive symptom management.

Case Report: We present the case of a patient presenting to the emergency department (ED) with acute-onset severe left forearm pain with associated pruritic rash incurred while working in a retail store. Initial therapeutic management included administration of analgesics, antihistamines, and steroids. After obtaining a comprehensive history and consulting with the Poison Control Center, we suspected an asp caterpillar envenomation. Following extraction of the caterpillar spines with silk tape, the patient’s symptoms improved. After a period of observation in the ED, the patient was discharged home without any known sequelae.

Conclusion: Although asp caterpillars typically inhabit trees and foliage, human exposure to the caterpillar may occur in developed environments. Effective history-taking, prompt communication with toxicologic experts, and complete removal of intact spines are essential for early identification and effective clinical management of asp caterpillar envenomation.