The Full Story
Caterpillars cause a surprising number of stings for such small creatures. In the US, several types of caterpillars can cause misery to humans who touch them. Among them are the saddleback, io moth, puss, gypsy moth, flannel moth, and buck moth caterpillars.
Caterpillars feed on leaves as they grow from eggs, before they develop into pupa and finally into adult moths. Unintentional human contact occurs when people brush against caterpillars they don't see. That can easily happen in a yard or garden. It's especially hard for people who work in caterpillar-infested areas to avoid contact.
Most problems from caterpillar exposures are due to tiny hairs (setae) or actual spines on a caterpillar's body. Some cause allergic reactions. A few of these insects contain a toxin and can actually cause poisoning, though that is not common in the US. For some caterpillars, their setae can blow on the breeze and land on skin, eyes, and clothing; this is common with gypsy moth caterpillars. From time to time, a young child will do what young children often do: pick up something interesting and try to eat it.
Preventing caterpillar exposures can be difficult, as they often are feeding on the underside of leaves. Wearing a hat and gloves while gardening can help.
Symptoms occur when the setae or spines contact human skin. Pain, itching, and a rash are common. Blistering and swelling are possible. If setae blow into the eyes, eye irritation is expected. (Some caterpillars can cause system-wide effects; that's not expected from caterpillars in the US.)
A history of caterpillar exposure makes diagnosis easy. If caterpillar contact isn't documented, the symptoms can look like a lot of other conditions. Treatment involves removing the hairs or spines from the skin, then treating the symptoms.
To treat a caterpillar exposure:
- If the caterpillar is on the skin, remove it without using your hands!
- Gently put tape over the exposed area, sticky side down. (Any kind of tape will do.)
- Pull up the tape, removing the hairs or spines.
- Repeat with fresh pieces of tape as often as needed to treat the area involved.
- Wash the area gently with soap and water.
- If the area itches, put on a paste of baking soda and water.
- If that doesn't help, try a hydrocortisone cream.
- If that doesn't help, try an antihistamine cream. That shouldn’t be the first choice, as it doesn't always help. Also, some people have skin reactions to these creams.
- If the area is badly blistered, contact your health provider.
- Call your health provider about a tetanus booster if your shots are not up to date.
You can always call Poison Control at 1-800-222-1222 or use the webPOISONCONTROL® online tool for treatment guidance for caterpillar stings. Both services (phone and online guidance) are available 24 hours a day.
Rose Ann Gould Soloway, RN, BSN, MSEd, DABAT emerita
Claudet I, Maréchal C. A transatlantic caterpillar. Pediatr Emer Care. 2009;25:186-187.
Hossler EW. Caterpillars and moths: part I. Dermatologic manifestations of encounters with Lepidoptera. J Am Acad Dermatol. 2010;62:1-10.
Hossler EW. Caterpillars and moths: part 2. Dermatologic manifestations of encounters with Lepidoptera. J Am Acad Dermatol. 2010;62:13-28.
Paraska KK. Caterpillar stings – a case study. AAOHN J. 2009;57:402-403.
- When possible, avoid areas infested with caterpillars.
- Wear a hat and gloves while gardening.
- If a caterpillar is stuck to the skin, remove it with a stick or tool. Do not touch it with bare hands.
- Teach children to leave caterpillars alone!
This Really Happened
Case 1: A woman brushed her pinky finger against a saddleback caterpillar. She had a lot of redness, blistering, and pain, with a burning sensation that extended into her forearm. She tried ice, baking soda paste, hydrocortisone ointment, other skin creams, and oral antihistamines. Nothing provided relief. Several hours later, she called Poison Control and was advised to put some tape onto her finger, sticky side down, then pull up on the tape. She did so and pulled the tiny caterpillar hairs out of her skin. The burning went away soon after and the pain decreased. She was able to treat the remaining redness and blistering with an ointment containing hydrocortisone and an antibiotic.
Case 2: At school, a teenager put his hand onto a stair rail; he didn't see the puss caterpillar there on the railing. The sting area was red and painful. The student applied tape to remove the tiny hairs. He washed the area, used a hydrocortisone cream on the site, and took diphenhydramine (an antihistamine). His pain and redness went away quickly. By the next day, his hand looked normal.