Urticating Caterpillars in Florida: 3. Puss Caterpillar and Flannel Moths

The flannel moths (family Megalopygidae) include some of the most commonly encountered poisonous caterpillars in Florida. They have urticating or “stinging” spines and setae, a well-known chemical defense found in several families of Lepidoptera. A previous circular (Heppner 1995) described the related slug caterpillars (family Limacodidae). All Megalopygidae apparently have stinging spines, although in some species they are more developed than in others and many smaller species are not generally encountered. The most common one in Florida is the puss caterpillar, Megalopyge opercularis (J.E. Smith). This species has the full setal pattern, falsely giving it a smooth and harmless appearance, while the upright poison spines (Fig. 8) are hidden beneath the long covering setae. The other general larval form found in this family, as in the caterpillar of the white flannel moth (Norape ovina Sepp), has the setae reduced in number, with clumps of spines more clearly evident (Fig. 7).

The urticating property of the larvae is due to a poison gland at the base of each seta (Figs. 8-9). A toxin is injected whenever a seta is touched and broken (Gilmer 1925). The chemical nature of urticating poisons is not fully known, but some caterpillar glands have been found to contain formic acid or histamine (Beard 1963).