Kentucky is home to several species of stinging caterpillars that can cause reactions ranging from mild itching to severe pain, swelling, and blistering. The most commonly reported are the puss moth caterpillar and the white flannel moth caterpillar, but others, including the saddleback, io moth, buck moth, and spiny oak slug caterpillar, also carry venomous spines. Most encounters happen in late summer and early fall when caterpillars are at their largest and feeding heavily on common shade trees.
How Stinging Caterpillars Deliver Venom
Stinging caterpillars don’t bite. Instead, they’re covered in hollow spines or hairs connected to venom glands. When you brush against one, even lightly, those spines break off in your skin and release an irritating toxin. Some species hide their venomous spines beneath a layer of soft, harmless-looking fur, which is exactly what makes the puss caterpillar so deceptive. You don’t need to pick one up to get stung. Leaning against a tree trunk, grabbing a branch, or brushing past a leaf where one is feeding is enough.
The Puss Caterpillar: Kentucky’s Most Painful
The puss caterpillar is the species most likely to send you searching for answers. About one inch long, it looks like a tiny toupee: a dense, woolly coat of soft brown hair with a tail-like tuft at the rear. It appears completely harmless, almost inviting to touch. But hidden beneath that long fur are rows of short, sharp venomous spines that can cause severe irritation on contact.
Puss caterpillar stings are consistently more severe than those of other stinging caterpillars, and the pain intensifies with the size of the caterpillar. A fully grown one in late summer delivers a worse sting than a smaller one earlier in the season. Reactions range from a burning, throbbing pain at the sting site to swelling, blistering, dermatitis, and in some cases even intestinal disturbances like nausea. The swelling and pain can last for days.
You’ll find puss caterpillars on a wide variety of Kentucky trees and shrubs, including apple, elm, maple, hackberry, oak, and sycamore. They’re not picky eaters, which means they can show up in yards, parks, orchards, and along sidewalks where branches hang low.
Other Stinging Species to Watch For
The white flannel moth caterpillar is the other frequently reported stinging species in Kentucky. It’s a yellowish-white caterpillar with tufts of stinging hairs along its body. Like the puss caterpillar, it feeds on deciduous trees and delivers a sting that can cause pain and swelling lasting several days.
Beyond those two, several other species carry venomous spines:
- Saddleback caterpillar: Easy to identify by its bright green body with a brown, saddle-shaped marking on its back. It has prominent spiny horns at both ends and shorter spines along the sides. The sting is sharp and immediate.
- Io moth caterpillar: A pale green caterpillar with red and white lateral stripes and clusters of branching green spines. It often feeds in groups on a wide range of trees and shrubs, so you may encounter several at once.
- Buck moth caterpillar: Dark-bodied with branching spines, commonly found on oaks. It tends to appear in spring and is frequently encountered in wooded areas.
- Spiny oak slug caterpillar: Small and flattened with spiny projections, typically found on oak leaves.
All of these species share the same basic defense mechanism: hollow, venom-filled spines that break off in your skin on contact.
What a Sting Feels Like
Most stings produce an immediate, sharp burning sensation at the contact site. Within minutes, the area often turns red and begins to swell. A grid-like pattern of raised welts may form where the spines entered the skin. For milder stings (from smaller caterpillars or brief contact), this may fade within a few hours.
More severe stings, particularly from puss caterpillars, can cause pain that radiates outward from the sting site into nearby joints or lymph nodes. Blistering and significant swelling are common, and the discomfort can persist for several days. Some people experience nausea or general malaise.
Serious allergic reactions are uncommon but possible. Shortness of breath, difficulty swallowing, and extreme swelling are warning signs. There have been rare reports of anaphylactic reactions to caterpillar stings. In very rare cases involving certain venomous species, complications can include brain bleeding, kidney damage, slurred speech, and loss of coordination.
What to Do After a Sting
The first priority is removing the spines still embedded in your skin. Press a strip of adhesive tape (duct tape works well) firmly over the sting site, then peel it away. Repeat several times with fresh pieces of tape to pull out as many spines as possible. Don’t rub the area with your hands or a cloth, which just pushes the spines deeper and spreads them around.
Once the spines are removed, wash the area with soap and water. Applying ice helps reduce swelling and numbs the pain. Over-the-counter hydrocortisone cream or antihistamines can ease itching and inflammation. Avoid scratching, which can break the skin and invite infection.
If the pain is severe and doesn’t improve with home treatment, or if you notice extreme swelling, difficulty breathing, or any signs of a systemic reaction, seek medical attention promptly.
How to Avoid Encounters
Stinging caterpillars are most active from midsummer through early fall, when they’re feeding heavily before pupating. Late August and September tend to bring the most reports in Kentucky. Since many species feed on extremely common trees like oaks, maples, and elms, encounters can happen almost anywhere with tree cover.
Wear gloves when pruning trees or handling firewood. Before leaning against a tree or sitting under one, take a quick look at the trunk and lower branches. Teach children not to handle caterpillars, especially fuzzy ones. The soft, furry appearance of puss caterpillars makes them particularly tempting for kids to pick up. Even dead caterpillars and shed skins can retain their venomous spines, so avoid handling them at any stage.
If you’re doing yard work around oaks, sycamores, or maples and notice caterpillars on the foliage, wearing long sleeves and checking your clothing before going indoors can prevent an accidental sting. Caterpillars sometimes drop from branches onto people below, so a hat isn’t a bad idea either.