Adult flannel moths are chunky-bodied, and the bodies, legs, and wings are very hairy, giving them a fluffy appearance. Most are whitish, yellowish, or brownish, with few markings. The females have thin antennae and males have featherlike antennae; often, the two sexes have slightly different colorations, too.
Caution! The fuzzy, hairy, silky caterpillars in this moth family can sting. They do not actively attack people, but if you brush against these caterpillars, stinging hairs, hidden among nonstinging hairs, can poke into your skin and break off, and venom inside the hairs or spines can penetrate your skin (this is a lot like the spines of stinging nettle plants). Reactions vary depending on the type of caterpillar and a person’s individual sensitivity. Stinging, itching, burning, rash, lesions, dermatitis, swelling, even fever and even nausea can result.
Caterpillars of flannel moths differ from those of all other butterflies and moths by their number of prolegs. Prolegs are the fleshy, peglike legs along the abdominal segments (that is, behind the pointy, jointed thoracic legs at the front of the caterpillar). Flannel moth caterpillars have 7 pairs of prolegs, while all other butterfly and moth caterpillars have 5 or fewer pairs.
Caterpillars in many moth families have stinging or irritating hairs, but then again, not all hairy caterpillar species necessarily can irritate or sting. If you are uncertain about the identification of any hairy or spiny caterpillar, dead or alive, it’s best not to touch it.
Most US flannel moths are limited to the desert southwest or the extreme southeast (especially Florida). Apparently three species are likely to be found in Missouri:
- Southern flannel moth (Megalopyge opercularis) adults are golden yellow, grading to paler beige at the rear. The hairy legs are black. The caterpillars, called puss caterpillars, can appear teardrop-shaped. They reach about 1½ inches long and are densely covered with fine gray or tan hairs that taper in back to form a tail. A crest of rusty hairs rise up along the back of the caterpillar, and a few patches of whitish hairs occur in tufts along each side of the back ridge. They eat leaves of a variety of deciduous trees and shrubs. They look like kitty cats, but do not touch them — their stings can be intense, to the point of requiring medical attention.
- Black-waved flannel moth, or crinkled flannel moth (M. crispata) adults are cream-colored with black, wavy lines along the leading edge of the forewing. Leg tips are black. Males are more intensely colored, females are paler. The caterpillars look a lot like those of the southern flannel moth, but they lack the “tail” of hairs extending from the rear. Hairs can be long and wispy or short and rather crinkly. Colors can vary widely, from white to cream to caramel to red. They feed on a wide variety of trees and shrubs, including oaks, plums, sassafras, willows, and more.
- White flannel moth (Norape ovina) adults are all white and are very hairy around the head and thorax. Males have yellowish, featherlike antennae. The caterpillars reach about 1¼ inches long and look polka-dotted with yellow on black. Basically, they are yellow with a wide dark stripe down the back. On the black stripe are 2 rows of yellow raised circles bearing clusters of short hairs. There are additional clusters of hairs along the sides. Longer hairs occur sparsely over the entire body. It eats leaves from a variety of trees, especially redbud, honey locust, hackberry, and mimosa.