Louisiana is home to several species of stinging caterpillars, but the buck moth caterpillar is by far the most common culprit. These purplish-black, spine-covered larvae show up on oak trees every spring, and both people and pets get stung regularly. A few other species, including the puss caterpillar (locally called an “asp”), the io moth caterpillar, and the saddleback caterpillar, also turn up across the state and pack a painful punch.
Buck Moth Caterpillar: Louisiana’s Most Common
The buck moth caterpillar is the stinging caterpillar most Louisianans encounter. Mature larvae are 2 to 3 inches long, purplish black, and covered in rows of branching spines that are hard to miss. Each of those hollow spines contains venom, and because they’re packed so closely together, a single brush against one caterpillar typically drives multiple spines into the skin at once.
Live oaks are their preferred host tree, though they’ll feed on other oak species too. Female buck moths emerge from the ground in late fall (November through mid-December) and lay eggs in circular clusters on smaller branches high in the canopy. Those eggs hatch between mid-February and April, and the larvae feed on oak leaves and grow quickly. The peak sting season runs from March through May, which is when the caterpillars are large enough to be noticed and common enough to be a real nuisance.
Once the caterpillars are fully grown, they crawl down the trunk as a group and burrow into the soil to pupate, staying underground until the cycle repeats the following fall. This group descent is when many stings happen: the caterpillars end up on sidewalks, driveways, porches, and anywhere else near an oak tree. In neighborhoods with mature live oaks lining the streets, stepping on one barefoot or brushing against one while gardening is a springtime rite of passage.
Puss Caterpillar (Asp)
The puss caterpillar, often called an asp in Louisiana and Texas, looks nothing like the buck moth larva. It’s small, teardrop-shaped, and covered in soft, tan or grayish fur that makes it resemble a tuft of cotton or a tiny Persian cat. That innocent appearance is deceptive. Hidden beneath the fur are venomous spines that cause what many people describe as the most painful caterpillar sting in North America.
When a puss caterpillar is pressed against the skin, its venomous hairs embed and typically cause severe burning and a rash. The pain usually subsides within about an hour, but more severe reactions can include swelling, nausea, and difficulty breathing. Some people develop a grid-like pattern of red marks on the skin that mirrors the arrangement of the spines underneath the fur. Puss caterpillars feed on a wide variety of trees and shrubs, so they’re not limited to oaks the way buck moths are. You might find one on an elm, citrus tree, or rose bush.
Io Moth and Saddleback Caterpillars
Two other stinging species show up in Louisiana less frequently but are worth recognizing.
The io moth caterpillar is bright green to yellow, about 2 inches long at maturity, with a narrow red stripe bordered by a white line running along each side. Its body is covered in branching, black-tipped yellow spines. Those spines are hollow and connected to venom sacs, just like the buck moth’s. The bright coloring is easy to spot but also easy to mistake for a harmless garden caterpillar if you don’t know what to look for.
The saddleback caterpillar is one of the more visually distinctive insects you’ll come across. Its body is brown at both ends and green in the middle, with a dark purple or brown oval spot centered on the green “saddle.” Two fleshy horns protrude from the front and rear, each bristling with spines. Stings from saddleback caterpillars can cause severe irritation. They’re smaller than buck moth caterpillars but compensate with potent venom.
What a Sting Feels Like
All stinging caterpillars work the same basic way. Their hollow, quill-like hairs are connected to venom sacs. When the hairs pierce your skin, they release that venom on contact. The immediate sensation is a sharp, burning pain, often compared to a wasp sting or touching a hot surface. Within minutes, you’ll typically see redness, raised welts, or a rash at the sting site. Some people also develop blistering or a broader area of swelling over the next few hours.
For most people, the pain peaks quickly and fades within an hour or two. The rash and irritation can linger for a day or longer. Reactions vary a lot from person to person, and repeated stings over the years can sometimes make reactions worse rather than building tolerance.
In rare cases, a sting triggers a systemic reaction: widespread swelling, nausea, abdominal pain, headache, swollen lymph nodes, or difficulty breathing. These reactions require immediate medical attention, as they can progress to shock or severe respiratory distress. This is more likely with puss caterpillar stings than with other species, and people with a history of strong allergic reactions to insect stings are at higher risk.
First Aid for a Caterpillar Sting
The most important step right after a sting is removing the spines still embedded in your skin. Wash the site with soap and water to flush away any loose hairs and let it air dry. Don’t rub the area with a towel, which can push spines deeper or break them off beneath the surface.
Once the skin is dry, press a strip of adhesive tape (duct tape works well) firmly over the sting site and peel it off. Repeat several times with fresh strips. This pulls out spines that washing alone won’t dislodge. After the spines are removed, applying ice and an over-the-counter hydrocortisone cream or antihistamine can help with pain and itching.
How to Avoid Getting Stung
During peak season (March through May for buck moths), watch where you step under oak trees, especially live oaks in residential areas. Caterpillars descend from the canopy when they’re ready to pupate, and they end up on trunks, low branches, sidewalks, and playground equipment. Wearing shoes outdoors and gloves while gardening eliminates most casual contact.
If you have young children or pets, check the ground beneath oaks before letting them play. Dogs are commonly stung on the nose or paws. For severe infestations on a yard tree, contact a licensed pest management professional. Spraying the canopy of a large live oak is not a realistic DIY project, and over-the-counter insecticides rarely reach the caterpillars feeding high in the tree.
Puss caterpillars and saddlebacks are harder to avoid because they feed on many different plants. The best defense is simply learning to recognize them and not touching any fuzzy or spiny caterpillar you don’t positively identify as harmless.