Urticating Caterpillars in Florida: Slug Caterpillars

Urticating or “stinging” spines and setae of some caterpillars are a well-known chemical defense found in several families of Lepidoptera. A previous circular (Heppner 1994) described the Io Moth (Saturniidae) and presented general notes about stinging spines and dermal reactions (Rothschild et al. 1970; Wirtz 1984 ). Herein, the slug caterpillars, which include some of the most well-known examples of stinging caterpillars, are discussed. All Limacodidae apparently have stinging spines, although in some species they are more developed than in others. Some examples of Florida slug caterpillars and adults are shown in the accompanying plates (line drawings are reproduced from a series of articles by Dyar (1895-99), with various details of spines and other larval features). There are 25 species recorded for Florida. The most commonly encountered is the saddleback caterpillar, Acharia stimulea (Clemens) (formerly in the genus Sibine) (Plate 1, Figs. 1-3; Plate 2). A number of species of this genus occur in the Neotropics, but only one is resident in the United States. Other species in Florida that are common include the hag moth (Phobetron pithecium (J. E. Smith)) (Plate 1, Fig. 8); Plate 4), Nason’ s slug caterpillar (Natada nasoni (Grote)) (Plate 3), the skiff moth (Prolimacodes badius (Hubner)) (Plate 1, Fig. 5; Plate I 0), the spiny oak-slug caterpillar (Euclea delphinii (Boisduval)) (Plate Plate I, Fig. 6; Plate 5), and the stinging rose caterpillar (Parasa indetermina (Boisduval)) (Plate I. Fig. 4; Plate 6).

The urticating property of the setae of the larvae is due to a poison gland at the base of each seta. A toxin is injected into the skin 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).