The Puss Moth Caterpillar, aka the "Asp"
The best known flannel moth and stinging caterpillar in Texas is the puss moth caterpillar, Megalopyge opercularis, commonly called an "asp". This is one of the most toxic caterpillars in North America. This caterpillar may infest shade trees and shrubbery around homes, schools, and in parks. They are of little importance as enemies of shade trees, but they can cause a severe sting. When a puss moth caterpillar rubs or is pressed against skin, venomous hairs stick into the skin, causing a severe burning sensation and rash.
Puss moth caterpillars are teardrop-shaped, and, with their long, silky hairs, resemble a tuft of cotton or fur. Their color varies from yellow or gray to reddish-brown, or a mixture of colors. The mature larva is 1 to 1 1/2 inches long with seven pairs of prolegs (suction-cup like claspers on the rear of the body). The adult moth has blunt wings covered with long, wavy hair and a wingspan of 1 to 1 1/2 inches. Wings are orange at the base, fading to cream-colored at the tips. Among the long body hairs are shorter spines that discharge venom upon contact. The head and legs are not visible from above.
Puss moth caterpillars can pose a genuine health hazard. Intense, throbbing pain develops immediately or within five minutes of contact with the caterpillar. Stings on the arm may also result in pain in the axillary (armpit) region. Erythematous (blood-colored) spots may appear at the site of the sting. Other symptoms can include headaches, nausea, vomiting, intense abdominal distress, lymphadenopathy, lymphadenitis, and sometimes shock or respiratory stress. Pain usually subsides within an hour and spots disappear in a day or so -- however, with a larger dose of the venom, it is not uncommon for the symptoms to last up to 5 days.
FIRST AID: An ice pack should be applied to the site of the sting, and oral antihistamines can be administered to help relieve the itching and burning sensations. For caterpillars with stout spines (such Io moth and saddleback caterpillar), try carefully applying cellophane tape to, and stripping it from, the sting site. This helps remove the irritating spines. For allergic reactions, such as generalized itching or difficulty breathing, see a physician immediately. For severe pain physicians sometimes administer meperidine HCl, morphine, or codeine; aspirin is reportedly not effective. Eye injuries should also be referred to a specialist immediately.