Bug Biz: Pest Management and Insect Identification Series - Io Moth

Forest Huval, Ring, Dennis R., Pollet, Dale K., Reagan, T Eugene


Io moth caterpillars (Automeris spp.) are typically light green, spiny and have a red and white stripe on the side of the body. The body is covered with structures bearing green stinging spines. Some larvae grow up to 2.4 inches (6 cm) when mature. This stinging caterpillar may be found on many shade trees and ornamentals. Adults are distinctive because of the prominent eyespots in the middle of the hind wing. Caterpillars are polyphagous, feeding on a wide variety of plants.


Io moth caterpillar. Robert L. Anderson, USDA Forest Service, Bugwood.org.


Adult Io moth. Lacy L. Hyche, Auburn University, Bugwood.org.

Sting Reactions

The entire larval body is coated with spines. Stings commonly result in an almost immediate painful nettling and itching reaction followed by formation of a localized welt and a reddened flare around the welt. The pain usually subsides within a couple of hours, and the welt and swelling subside within six to eight hours. Allergies to these stings have been documented, and stings should be watched for any potential anaphylactic reaction. Other symptoms that are documented include headache, fever, nausea, vomiting, heart arrhythmia (abnormal heart beat), hypotension (low blood pressure), acute abdominal pain and muscle spasms.

Care of Stings

To relieve pain, antihistamines should be taken and a cold compress applied. The pain can last over 24 hours. Remove urticating hairs and spines using adhesive tape. Wash the stung area with soap and water or a sterilizing agent and allow to air dry. If you suspect an allergic reaction, or if stung regions are accompanied by abdominal pain and intense muscle spasms, see a doctor for appropriate medical attention.

Seasonality and Control

The Io moth has two generations per year, with the caterpillars active between April and the beginning of July and the second generation appearing from August until October. They pupate over winter. Caterpillars crawl down from the host plants and spin cocoons in leaf litter or protected places, like crevices and logs or rocks. The Io moth has a variety of predators during its life cycle, including birds, mammals, spiders and other insects. Several species of tachinid flies are parasitoids of the Io moth and provide additional biological control. This moth rarely causes major injury to the plant, so control is rarely necessary.

Io Moth Chartpng


Diaz, James H. 2005. The epidemiology, diagnosis, and management of caterpillar envenoming in the southern US. The Journal of the Louisiana State Medical Society: Official Organ of the Louisiana State Medical Society 15: 153-157.

D. K. Pollet and Ring, D. R. 2006. Stinging Caterpillars. Bug Biz. Pub 1979. 2 pgs.

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