As a young boy, I found out first hand that some caterpillars can produce some painful results. We often get calls this time of year about these stinging caterpillars. Recognizing the few stinging caterpillar species, including the saddleback, may prevent irritating encounters.
The saddleback caterpillar measures about an inch long and has poisonous spines on four large projections (tubercles) and many smaller ones projecting from the sides of its body. The “saddle” consists of an oval purplish-brown spot in the middle of a green patch on the back. The saddleback caterpillar is a general feeder and can be found on many hosts including corn foliage, apple, cherry, basswood, chestnut, pecan, oak, and other trees in late summer.
Diagnosis of saddleback stings are simple. A rash generally breaks out where the hairs or spines have made skin contact. Contacting the hollow poisonous hairs or spines (connected to underlying poison glands) causes a burning sensation and inflammation that can be as painful as a bee sting. The irritation can last for a day or two. Usually the site of contact reddens and swells much like a bee sting.
Immediate application and repeated stripping with adhesive or transparent tape over the sting site may be helpful in removing broken hairs or spines. Washing the affected skin area thoroughly with soap and water may help remove irritating venom. Prompt application of an ice pack should help reduce pain and swelling. Oral administration of antihistamines may help relieve itching and burning. Topical corticosteroids may reduce the intensity of inflammatory reaction. Prompt referral to and treatment by a physician should be make when severe reactions are evident. Very young, aged or unhealthy persons are more likely to suffer severe reaction symptoms.
These stinging hair caterpillars may drop out of trees onto people, occur on outdoor furniture or sting when brushed against on plant foliage. Be careful when attempting to brush them off. Never swat or crush by hand. Remove them carefully and slowly with a stick or other object.
Individuals, especially children, should be cautioned about handling or playing with any colorful, hairy-like, fuzzy caterpillars since it is sometimes difficult to distinguish between harmless and venomous insect larvae. Never handpick these hairy, fuzzy, or spiny caterpillars except with heavy gloves if necessary. Wear long sleeve shirts, trousers, and gloves when harvesting sweet corn or working in the landscape in late-summer and early-autumn to reduce possible stings.
Usually these stinging hair caterpillars do not occur in sufficient numbers to justify the use of pesticide sprays. Should potential hazards exist around residences or schools, infested shrubs and trees may be sprayed to reduce or eliminate these caterpillars. Sprays of carbaryl (Sevin) or Bacillus thuringiensis (Biotrol WP or Thuricide) in formulations labeled for bushes, shrubs, and trees can be helpful. Be sure to read the label, follow directions and safety precautions.