It may appear cute, fuzzy, and pettable, but this pile of fluff attached to a grass blade at the Sandylands Sanctuary in East Texas is best avoided. A larval stage of the Black-Waved Flannel Moth (Megalopyge crispata), its hollow hairs contain toxins designed to protect the caterpillar from predators.
When other creatures — including humans — brush against the hairs, they break away and release the toxin, producing a painful rash or sting. Depending on the species and a person’s sensitivity, swelling and inflammation, numbness, or even fever and nausea might result.
While younger Black-waved flannel moth larvae sport long, white wispy hairs, in their final larval stage they look very much like the best known stinging caterpillar in Texas: the Southern Flannel moth (Megalopyge opercularis). Commonly known as puss moths, or ‘asps,’ they can be abundant in live oak, pecan, elm, and hackberry trees, as well as in yaupon and other shrubs.
Occasionally, they’ll drop from the trees onto cars or pavement below. When I found one on my car yesterday, it served as a timely reminder that their season has arrived.
Venomous hairs hidden beneath the silky outer hairs of the asp can deliver a sting even more painful than that of the Black-Waved flannel moth. Intense, throbbing pain can develop immediately upon contact, and other symptoms can include headaches, nausea, vomiting, and sometimes shock or respiratory stress. After my own first (and only) encounter with one of these critters, it took a day for the pain to subside, and several days for the red marks to disappear.
First aid advice for these caterpillar stings includes ice packs, baking soda, and the use of adhesive tape to pull broken spines out of the skin, but prevention — learning to recognize and avoid these caterpillars — beats every cure in the book.