• Topics: Entomology and Nematology  | Moths  |  Featured Creatures collection  | Family: Saturniidae (giant silkmoths, royal moths, emperor moths, etc)  | Heppner, John B 

Io moth, Automeris io (Fabricius) (Insecta: Lepidoptera: Saturniidae)¹

Introduction

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, Saturniidae, 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 Saturniidae) 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 saturniid caterpillars (Lonomia achelous (Cramer)) in Venezuela, which have poison spines containing an anticoagulant (Marwh 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), Saturniidae), 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.

Figure 1. 

Caterpillar of the io moth, Automeris io (Fabricius), showing groups of urticating spines.

The urticating setae of the io larvae are shown greatly enlarged in the drawing below. Two types of poison spines are found, both having a poison gland (Glimer 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). Urtication 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.

Figure 2. 

Poison spines of io moth caterpillar.

Distribution

Io moths are common throughout eastern North America, north to southern Canada. They range west to southern Arizona and south to Central America, at least as far as Costa Rica. Over 200 species of Automeris and related genera in Hemileucinae occur south of the U.S. border (Collins and Weast 1961).

Identification

The io moth adult is 2.0 to 3.5 inches (50 to 87 mm) in wingspan and easily recognized by the large eye-spots of the hindwings. Adult males are mostly yellow, while females have brown forewings. Subspecies A. io lilith (Strecker) of Florida has male adults with distinctly red-brown forewings, especially in south Florida; the same type of red form is also found in southern Mexico and the Bahamas. The larvae have characteristic long yellow or green spines covering most of the body. Only a few other caterpillars may look similar, but these do not have the well-defined red and white lateral line. The io moth caterpillar has at least three discrete color forms: the usual last instar form is light green, with a distinct lateral body strip of red and white. Earlier instars are yellow overall and the lateral line is reduced. There also is a blue-green color form of last instars (Collins and Weast 1961).

Figure 3. 

Adult io moth, Automeris io (Fabricius).

Figure 4. 

Early instar larvae of the io moth, Automeris io (Fabricius).

Figure 5. 

Last instar larva of the io moth caterpillar, Automeris io (Fabricius).

Biology

Io moth larvae are leaf feeders, gregarious in early instars, then solitary as they grow. After several weeks of feeding, they make a simple paper-like cocoon away from the host plant. In Florida, there are three to four generations per year. There usually is only one generation in northern states.

Host Plants

Io moth larvae are leaf feeders, gregarious in early instars, then solitary as they grow. After several weeks of feeding, they make a simple paper-like cocoon away from the host plant. In Florida, there are three to four generations per year. There usually is only one generation in northern states.

Management

If present in large numbers, caterpillars can be sprayed with a bacterial spray (Bacillus thuringiensis) or any common insecticide although usually the larvae are not so common as to warrant spraying. Larvae should not be touched. Remedies for relief of urticating pain include initial removal of any remaining inserted spines by the use of adhesive tape, followed by ice compacts, mentholated vaseline, or an antihistamine medicine (Riley and Johannsen 1938; Frazier and Brown 1980).

Selected References

Beard, RL. 1963. Insect toxins and venoms. Annual Review of Entomology 8:1-18.

Biery, TL. 1977. Venomous arthropod handbook. U.S. Government Printing Office, Washington. AFP-161-43. 40 p.

Collins, MM, and RD Weast. 1961. Wild silk moths of the United States. Collins, Cedar Rapids. 138 p.

Fasulo, TR. 2005. Stinging caterpillars and caterpillars of ornamental plants. Bug Tutorials. University of Florida/IFAS. CD-ROM. SW 177.

Fasulo, TR, W Kern, PG Koehler, DE Short. 2005. Pests In and Around the Home. Version 2.0. University of Florida/IFAS. CD-ROM. SW177.

Frazier, CA. 1969. Insect allergy: allergic and toxic reactions to insects and other arthropods. W.H. Green, St. Louis. 493 p.

Frazier, CA, and FK Brown. 1980. Insects and allergy and what to do about them. University of Oklahoma Press, Norman. 272 p.

Gilmer, PM 1925. A comparative study of the poison apparatus of certain lepidopterous larvae. Annals of the Entomological Society of America 18:203-239.

Jones, DL and JH Miller. 1959. Pathology of the dermatitis produced by the urticating caterpillar, Automeris io. Archives of Dermatology 79:81-85.

Marsh, NA and CL Arocha-P. 1971. Observations on a saturniid moth caterpillar causing severe bleeding in man. Proceedings of the Royal Entomological Society of London 36: 9-10.

Matheson, R. 1950. Medical entomology. (2nd ed.). Comstock Publications, Ithaca, New York. 612 p.

Murtfeldt, ME. 1876. An experiment with a stinging larva. Canadian Entomologist 8: 201-202.

Picarelli, ZP and JR Valle. 1971. Pharmacological studies on caterpillar venoms. pp. 103-119. In W. Bucherl and E. Buckley (eds.), Venomous animals and their venoms. Vol. 3. Venomous invertebrates. Academic Press, New York.

Riley, WA and OA Johannsen. 1938. Medical entomology; a survey of insects and allied forms which affect the health of man and animals. McGraw-Hill, New York. 483 p.

Roth, LM and T Eisner. 1962. Chemical defenses of arthropods. Annual Review of Entomology 7: 107-136.

Rothschild, J, T Reichstein, J von Euw, R Aplin and RRM Harman. 1970. Toxic lepidoptera. Toxicon 8: 293-299.

Valle, JR, ZP Picarelli, and JL Prado. 1954. Histamine content and pharmacological properties of crude extracts from setae of urticating caterpillars. Archives Internationales de Pharmacodynamie et de Therapie 98: 324-334.

Wirtz, RA. 1984. Allergic and toxic reactions to non-stinging arthropods. Annual Review of Entomology 29: 47-69.

Zak, RA. 1986. A field guide to Florida critters: common household & garden pests. Taylor Publishing, Dallas. 294 p.

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U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.

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