M. opercularis can be found on oak, elm, and wild plum, among others, as well as many garden plants such as roses and ivy. It is distributed throughout the Eastern United States between extreme southeastern Virginia and Florida, the Southern United States, Mexico, and parts of Central America. The caterpillar has two broods, one in the summer and the other in the fall. Late larvae may stay in their cocoon all winter, and emerge in late spring as an adult.

The caterpillar is regarded as a dangerous insect because of its venomous spines. Exposure to the caterpillar's fur-like spines leads to an immediate skin irritation characterized by a "grid-like hemorrhagic papular eruption with severe radiating pain." Victims describe the pain as similar to a broken bone or blunt-force trauma, or even white hot. The reactions are sometimes localized to the affected area, but are often very severe, radiating up a limb and causing burning, swelling, nausea, headache, abdominal distress, rashes, blisters, and sometimes chest pain, numbness, or difficulty breathing. Sweating from the welts or hives at the site of the sting is not unusual.

The venom from the spines is best treated within hours of first contact. For first aid, the spines (if present) should be removed by using cellophane tape. Some remedies, which are reported to have varying degrees of success, include ice packs, oral antihistamine, baking soda, hydrocortisone cream, juice from the stems of comfrey plants, and calamine lotion. The caterpillar sting causes a condition called urticarial dermatitis or erucism, with M. opercularis contact being the most commonly reported source in the United States.

• Data related to Megalopyge opercularis at Wikispecies
• Media related to Megalopyge opercularis at Wikimedia Commons
• Research on the Asp Caterpillar at Baylor College of Medicine
• Megalopyge opercularis on the UF / IFAS Featured Creatures website.