Looks can be deceiving: stinging caterpillars

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By MARION BARNES
Senior County Extension Agent
Clemson University

The old adage, “looks can be deceiving” certainly holds true, especially when it comes to the world of insects. Some of nature’s most colorful creatures can pack a potent punch. A cute, fuzzy, brightly colored exterior may actually hide a painful surprise.
Caterpillars are the immature stages of butterflies and moths. Although there are many species that are harmless, there a few stinging caterpillars that should be approached with caution. Most people are aware that bees, wasps, hornets and some ants will sting to defend themselves and their nests. Only a few people may realize, until firsthand experience, that certain caterpillars can produce painful stings.
Stinging caterpillars have hollow quill-like hairs that are connected to poison sacs and are for defense against predators. These hairs produce irritation and rashes when they come in contact with or pierce your skin. Reactions can range from mild irritation and itching to intense throbbing pain, swelling and inflammation, blistering and dermatitis. Other symptoms include headaches, nausea, vomiting and sometimes respiratory stress. Some individuals who are more sensitive to insect stings may be at even greater risk and should seek immediate medical attention if stung by these pests.
Stinging caterpillars usually show up in late summer or fall. One of the most common venomous caterpillars is the puss caterpillar. According to the United States Department of Agriculture, most caterpillar stings in the South can be attributed to the puss caterpillar, Megalopyge opercularis. They are also called “toxic toupees” because they resemble a mass of hair on a leaf. The moth of the puss caterpillar is the southern flannel moth and is found from New Jersey to Florida and west to Arkansas and Texas. Adult moths are small with wing spans of one to one-and-a-half inches, with females generally larger than males. The flannel moth gets its name from the thick fur-like coating of seta (bristles or flannel-like scales) that cover their bodies.

The moths are thought to lay their eggs in batches since young larvae feed in groups on leaf surfaces. There are 1-2 generations a year, usually around the fall (July through October). Larvae go through several instars (stages of development) before maturing. The mature caterpillar, which is about one inch in length, spins a unique-shaped cocoon where it spends the winter on the trunk or branches of host plants.
Caterpillars feed on numerous plants but are commonly found on various deciduous trees and shrubs, especially oak, pecan, hackberry, elm and sycamore.
Puss caterpillars are one of the most venomous caterpillars in the South. Spines are found beneath its soft furry setae (hair) and are hollow with a toxin gland at the base. The toxicity of caterpillars sting increases with its body size. When one comes in contact with a puss caterpillar or the caterpillar rubs against a person’s skin, its venomous spines are embedded, usually causing severe burning, pain and many other symptoms previously mentioned. More severe reactions may occur, and immediate medical attention is advised. The type of reaction will depend on the degree of contact and susceptibility of the individual.
Unintentional contact usually occurs when people brush up against caterpillars they do not see. Avoiding this stinging pest is especially difficult for individuals who work in caterpillar infested areas like the yard or garden. Timber cruisers sometimes encounter these caterpillars in the fall of the year when marking and evaluating timber stands, especially if live oaks are present on the property. An encounter with a puss caterpillar can be very painful and may even require a trip to the emergency room, as I learned a few years ago.
These caterpillars rarely cause serious damage to trees; however, they do pose a health hazard to children, gardeners and others who work in the outdoors. Control measures are limited, so the best option may be proper identification of the pest and the importance on avoiding stinging caterpillars.
For more information on stinging caterpillars, check out Home and Garden Information Center Fact Sheet HGIC 2482, Stinging Caterpillars. Contact your medical provider for first aid measures and treatment for caterpillar stings.

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