Buck moth caterpillars are one of Louisiana’s most dreaded seasonal pests, appearing in massive numbers across New Orleans and south Louisiana every spring. These dark, spiny caterpillars feed almost exclusively on oak trees, and their venomous spines deliver a painful sting that catches thousands of residents and visitors off guard each year. If you live under a live oak canopy, you’ve likely already had a run-in with one.
Why Louisiana Has So Many
Buck moth caterpillars are drawn to oak trees the way locals are drawn to a Friday lunch at Galatoire’s. Live oaks and water oaks, the signature trees lining streets across New Orleans, Baton Rouge, and towns throughout south Louisiana, are their primary food source. The dense, sprawling canopy that makes neighborhoods like Uptown and the Garden District so beautiful also creates ideal habitat for these caterpillars to thrive in enormous colonies.
They show up starting in late April or early May, taking up residence on branches and feeding heavily, mostly at night. You won’t spot them easily because their dark bodies blend in with the bark. But they’re up there by the hundreds, sometimes thousands, on a single tree. As they mature and grow larger over several weeks, they begin descending the trunks and dropping onto sidewalks, yards, playground equipment, and anyone unlucky enough to be underneath.
What a Sting Feels Like
Buck moth caterpillars are covered in branching spines that look like tiny black or reddish-brown antlers running down their bodies. These aren’t just prickly hairs. They’re hollow, quill-like structures connected to venom sacs at the base. When you brush against a caterpillar, even lightly, the spine tips break off in your skin and release venom directly into the tissue.
The initial sensation is a sharp, burning pain, often compared to a wasp sting but with a wider area of discomfort. Within minutes, the sting site turns red and begins to swell. A raised welt or series of welts typically forms along the line of contact. For most people, the pain peaks within the first 30 minutes and gradually fades over several hours, though itching and irritation can persist for a day or two. Some people develop blistering, more intense swelling, or a spreading rash that lasts longer. The severity depends on how many spines made contact and your individual sensitivity. People who’ve been stung before sometimes react more strongly, not less.
How to Treat a Sting
The most important first step is removing the tiny spines still embedded in your skin, because they continue releasing irritants as long as they’re in place. Press a piece of adhesive tape (duct tape works well) firmly against the sting site, sticky side down, then peel it off. This pulls the microscopic spine tips out of the skin. Repeat with fresh strips of tape several times to get as many as possible.
After removing the spines, wash the area with soap and water. Apply a hydrocortisone cream to reduce inflammation and itching. An over-the-counter antihistamine can help with swelling and the histamine response that drives the rash. Ice wrapped in a cloth and placed on the area for 10 to 15 minutes also helps with pain and swelling in the first hour.
Most stings resolve on their own within a day or two with these simple measures. But a small number of people experience systemic allergic reactions, including shortness of breath, difficulty swallowing, or extreme swelling that spreads well beyond the sting site. These are signs of a potentially serious reaction that needs immediate medical attention. Anaphylaxis from caterpillar stings is rare, but it has been documented.
Keeping Them Off Your Property
Timing matters more than anything when it comes to control. Young buck moth caterpillars cluster together in dense groups on branches, making them easiest to target early in the season before they disperse across the tree and start heading to the ground.
For young caterpillars, the LSU AgCenter recommends two low-toxicity options: Bt (a naturally occurring bacterial pesticide) and spinosad. Both are effective against small larvae and are safe to use around pets, kids, and beneficial insects when applied as directed. They work by being ingested as the caterpillars feed on treated leaves, so thorough coverage of the lower canopy matters.
For larger, more mature caterpillars that have spread out or started descending tree trunks, stronger products containing permethrin or bifenthrin are effective. These are common pyrethroid insecticides sold under various brand names at garden centers. Spraying the trunk from the ground up to about 10 feet can intercept caterpillars on their way down. Some homeowners also wrap tree trunks with bands of sticky material or duct tape (sticky side out) to trap caterpillars as they crawl to the ground.
Then there’s the simplest approach: stomping. Once caterpillars are on the ground, you can crush them with a shoe. Just be sure to wear closed-toe shoes, because the spines remain venomous even after the caterpillar is dead. Never handle them with bare hands, and use gloves if you’re picking them off outdoor furniture or play equipment.
Protecting Kids and Pets
Children are especially vulnerable because they play on the ground, lean against tree trunks, and are more likely to pick up something unusual they find on a sidewalk. The sting is more painful for smaller bodies, and kids are more prone to rubbing the sting site and then touching their eyes or mouth, which can trigger a more serious reaction. During peak caterpillar season in May and early June, it’s worth checking the ground under oak trees before letting kids play outside, particularly in neighborhoods with heavy canopy cover.
Dogs also get stung regularly, usually on their paws or noses. If your dog suddenly yelps, starts licking a paw obsessively, or develops facial swelling after being outside under oaks, a caterpillar sting is a likely cause. The same tape-removal technique works on short-haired areas, and a veterinarian can advise on appropriate antihistamine dosing for your pet’s size.
When the Season Ends
Buck moth caterpillars feed for roughly six to eight weeks before pupating underground. By mid to late June in most of south Louisiana, the caterpillars have left the trees and burrowed into the soil, where they’ll stay as pupae until the following fall. The adult buck moths emerge in October and November as striking black-and-white moths with a wingspan of about two to three inches. The adults don’t sting or feed. They mate, lay eggs in rings around oak twigs, and die within days. Those eggs overwinter on the branches and hatch the following spring, restarting the cycle.
This means the window of real concern is relatively narrow, roughly late April through mid-June, though the exact timing shifts a bit each year depending on winter temperatures and when the eggs hatch. Watching for the first reports from neighbors or local news is the best way to know when the season has started in your area.