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Sunday, May 5, 2002

IO Moth

Caterpillars are Putting a "Sting" Into Spring in Bexar County

Asp (Photo credit: B. Drees, Texas Cooperative Extension).

by Nathan Riggs, Extension Agent, Integrated Pest Management, Bexar County

Most people know that bees, wasps, hornets and some ants can sting to defend themselves or their nests. Only a few people realize, usually from first hand experience, that handling some caterpillars can produce some painful results. Recognizing the few stinging caterpillar species may prevent irritating encounters. Caterpillars that later become moths, often have spines and barbed hooks. Generally, these are for show and are quite harmless. An example is the Woolybear caterpillar shown below. The spiky black hairs could possibly be irritating to extra sensitive persons, but generally they are harmless.

 

Woolybear Caterpillar (Texas A&M University image)

A good example is the Black Woolybear caterpillar (very common in San Antonio). Here we show the Great Leopard Moth--the metamorphosis of the Black Woolybear.

Great Leopard Moth (Texas A&M University image)

Stinging caterpillars possess hollow quill-like hairs, connected to poison sacs, that are used as defensive weapons. When these hairs are touched they break through the skin releasing the poison. Reactions can range from a mild itching to the more severe pain, dermatitis, and even intestinal disturbances.

Slug-Like Caterpillars
There are several species of slug-like caterpillars that have poisonous spines. Slug caterpillars are short and stocky and creep about on leaves in a slug-like manner. The head and legs are not visible. Typically, there is one generation per year with the grown larvae found in the late summer.

The one-inch Puss Moth caterpillar (see photo top of page on the right), known to Bexar County folks as the "asp," is covered with a dense wooly coat of soft brown hair that lies flat against the body, with tail-like hairs at the rear end. Beneath the hairs are three rows of short, poisonous spines that inject venom and cause severe irritation. They are often found feeding on various trees and shrubs, including elm, maple, hack berry, oak, sycamore, ligustrum and others. Young caterpillars often feed in groups. Sting severity increases with size of caterpillar. Puss caterpillar stings are often more severe than those of other caterpillars. Adults of this caterpillar are an unobtrusive, fuzzy brown moth with a 1 to 1 ½ inch wingspan.

The Saddleback caterpillar is brown in the front and rear and green in the middle with a purple spot in the center of the green "saddle." There are prominent horns on the front and rear. Stings by this insect can cause severe irritation. Saddlebacks are typically found on deciduous trees such as basswood, chestnut, cherry, oak, and plum, but occasionally they can be found on corn. Again, the stinging spines on this caterpillar are borne in tufts on each end and around the edges of the body. (Photo at left credit: R. Bessin, Univ. of Kentucky).

The pale yellow-green Euclea caterpillar has four dark patches of spines toward the rear and numerous spiny, yellow or red fleshy lobes. Grown caterpillars have a brown area on the back. It feeds on oak, beech, flowering crabapple, willow, pear,bayberry, sour wood, wild cherry and other trees. It is less venomous than the saddleback caterpillar, but painful, nonetheless. At full size, it is one inch long. (Photo credit at right: Nathan Riggs, Texas Cooperative Extension).

How to Avoid Stings
Most encounters with stinging caterpillars result from accidently brushing against leaves on which they are feeding. The chances of running into these insects are relatively low, but occasionally one species may be very abundant. Also the more time spent in wooded areas, the greater the opportunity for contact. With the exception of puss caterpillars, most of these caterpillars are distinctly marked or brightly colored. This can allow you to see and avoid them. If you find one on yourself, don't brush it off or slap it with a bare hand. Use a stick or other object to remove it carefully. Hollow spines may break off in clothing or gloves.

First Aid for Stings
No truly effective home first aid treatments for caterpillar stings are available. Adhesive tape or transparent tape may be used to pull out some of the broken spines in the sting area. Washing the area thoroughly with soap and water may help remove some of the irritating venom. Prompt application of an ice pack or baking soda may help to reduce pain and prevent swelling. Antihistamine drugs, often administered for bee and wasp stings, are reportedly ineffective. See a physician if severe reactions occur. Very young, aged or persons in poor health are more likely to suffer severe reaction symptoms. With this in mind, remember that all people react differently to stings of any kind.

Control
Where stinging caterpillars are numerous or present hazards to people, such as around residences, recreation areas or schools, infested shrubs and trees may be sprayed to eliminate or reduce the caterpillars. Use products containing Bacillus thuringiensis or carbaryl for control. Bacillus products are most effective on the smaller stages of the caterpillars. Always read and follow label instructions. For more information on these caterpillars or to get an identification of a suspicious caterpillar, call the Bexar County Extension office at (210) 467-6575. You may also e-mail Nathan Riggs at the Extension office at n-riggs@tamu.edu as well.

References: Ric Bessin, Extension Entomologist (University of Kentucky)

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Last updated: May 6, 2003