Urticating Caterpillars in Florida: 1. lo Moth, Automeris io

The urticating or “stinging” spines and setae of some caterpillars are a well-known chemical defense found in several families of Lepidoptera, especially Megalopygidae, Limacodidae, Satumiidae, and a few Nymphalidae, Anthelidae, Lasiocampidae, Bombycidae, Eupterotidae, Lymantriidae, Arctiidae, and Noctuidae (Matheson 1950; Riley and Johannsen 1938; Roth and Eisner 1962; Wirtz 1984). Toxicity in Lepidoptera is also found in adults, where scales may be urticating in some families (Notodontidae (Thaumetopoeinae), Lymantriidae, Arctiidae, and Satumiidae) or where integumental glands produce an urticating chemical (Zygaenidae and Arctiidae) (Rothschild et al. 1970).

Poison glands in urticating Lepidoptera are mainly of interest for their effect on humans, or lepidopterism as it is called (Wirtz 1984). Persons of average sensitivity experience stinging sensations from touching the spines which contain poison glands. Persons of extreme sensitivity can experience severe pain and allergic reactions. Cases are known of hospitalization being required due to severe dermatitis. Severe allergic reactions could cause death in extreme cases. Skin bleeding results from contact with satumiid caterpillars (Lonomia achelous (Cramer)) in Venezuela, which have poison spines containing an anticoagulant (Marsh and Arocha-P. 1971). Murtfeldt (1876) provided one of the early reports with her own reactions to various caterpillars, finding the puss caterpillar capable of producing an extreme stinging sensation, along with extensive swelling that lasted several hours. Similar reactions are noted by Frazier (1969) and Frazier and Brown (1980). Cases of allergic reactions to Lepidopteran adults and larvae have been reported where workers handled larvae or inhaled excessive numbers of dislodged urticating scales from adult moths (e. g., Hemileuca and Hylesia spp.), resulting in dermatitis or asthma-like reactions (Wirtz 1984). Most persons develop some immunity after repeated incidents with urticating caterpillars or adult urticating setae, but at least two species are known that produce cumulative effects resulting in more severe reactions after each successive occurrence (the New Mexico range caterpillar, Hemileuca oliviae Cockerell, and the brown-tail moth, Euproctis chrysorrhoea (Linnaeus), from Europe) (Wirtz 1984).

In Florida, the main stinging caterpillars are the io moth (Automeris io (Fabricius), Satumiidae), the saddleback caterpillar (Acharia stimulea (Clemens) [formerly in Sibine], Limacodidae), and the puss caterpillar (Megalopyge opercularis (J. E. Smith), Megalopygidae) (Biery 1977; Zak 1986). All species of Limacodidae and Megalopygidae appear to have urticating larvae. Minor irritation is also reported from two North American Arctiidae (Euchaetes egle (Drury) and Lophocampa caryae Harris)), Noctuidae (Apatele spp., Catocala spp.), and Lymantriidae (Orgyia leucostigma (J. E. Smith)). Other hairy caterpillars are not known to cause reactions to persons of average sensitivity.

The urticating setae of the io larvae are shown greatly enlarged in Fig. 4. Two types of poison spines are found, both having a poison gland (Gilmer 1925). The chemical nature of urticating poisons is not fully known and not reported specifically for io moth larvae, but Jones and Miller (1959) noted the dermatitis that results from it. Some caterpillar glands have been found to contain formic acid (Roth and Eisner 1962). Related groups of saturniids (Dirphia spp.) have histamine as the poison (Beard 1963; Picarelli and Valle 1971 ; Valle et al. 1954). U rtication results from touching poison spines or setae, thereby breaking the tip and releasing the poisonous chemicals, or by injecting into the skin via a puncture when more forcefully contacted. Adult io moths do not have any urticating scales.