Puss Caterpillars: Why the Sting Hurts and Where They Live
The puss caterpillar is the larva of the southern flannel moth, Megalopyge opercularis, a furry, teardrop-shaped caterpillar about an inch long whose soft hair hides hollow venomous spines, making it one of the most venomous caterpillars in the United States. A sting causes immediate, intense burning pain and often a red grid of spots matching the spines. Most stings are minor: in 17 years of Texas poison centre reports, 93 per cent of patients had no or at most minor effects. It lives from New Jersey to Florida and west to Texas, mostly on oaks and elms.
It looks like a tuft of cotton or a tiny wig, which is exactly why children pick it up. Below: how to recognise it and the other stinging caterpillars it gets confused with, what the poison centre data says about stings, when it turns up, and what actually controls it.
Stinging caterpillars compared
| Caterpillar | What it looks like | Mature length | Common hosts | Usual season |
|---|---|---|---|---|
| Puss caterpillar (asp) | Teardrop of long silky hair, yellow, grey, tan or reddish brown, with a hairy tail | About 1 to 1.5 in (25 to 38 mm) | Oak, elm, citrus, pecan, hackberry, yaupon | Two broods: early summer and autumn |
| Saddleback | Green “saddle blanket” with a brown, white-ringed spot; spiny horns at both ends | About 3/4 in (19 to 20 mm) | Maple, hibiscus, crape myrtle, oak, cherry, corn | Late summer |
| Io moth | Pale green with a red and white side stripe; clusters of yellow green black-tipped spines | 2 to 2.5 in (51 to 65 mm) | Elm, maple, willow, hibiscus, wisteria, roses, corn | Not given in the sheets we used |
| Buck moth | Black with tiny white or yellow dots; rows of branched spines | 2 to 2.5 in (51 to 65 mm) | Oak, willow | Spring to mid summer; one generation |
| Hag moth (monkey slug) | Brown, like a dried leaf, with nine pairs of twisted hairy lobes | Small slug caterpillar | Oak, dogwood, chestnut, apple | Late summer |
| White flannel moth | Yellow with a black back stripe and raised yellow tufts | Up to 1.25 in (32 mm) | Redbud, honey locust, hackberry, mimosa | Later summer |
Compiled by The Pest Control Brief from UF/IFAS SP107 and EENY-545, University of Kentucky Entfact-003, NC State Extension and Texas A&M AgriLife.
The puss caterpillar is the only one in that table whose spines are hidden. Kentucky’s entomologists put it plainly: unlike other stinging caterpillars, the flannel moth’s venomous spines sit underneath longer silky hairs. UF/IFAS notes that people often mistake puss caterpillars as safe to handle because of that soft, furry look. The black-wave flannel moth caterpillar, Megalopyge crispata, looks very similar but lacks the long tail, and Kentucky says its sting is usually less severe.
How to identify a puss caterpillar
Texas A&M describes mature puss caterpillars as teardrop-shaped, 1 to 1.5 inches long, with long silky hairs that make them resemble a tuft of cotton or fur, in colours from yellow or grey to reddish brown. Like other flannel moth larvae they have seven pairs of prolegs rather than the usual five. In UF entomologist Donald Hall’s account, the head is normally hidden under the hair and shows only when the caterpillar moves or feeds, and late instars have a hairy tail that extends beyond the body. Hall’s own reared larvae reached about 3.5 cm (1.4 in) in body length and 4.0 cm (1.6 in) with the tail, a little larger than the one inch most fact sheets give.
Young caterpillars look different. Early instars are tiny (the first is about 1.5 mm, a sixteenth of an inch), yellowish and far less hairy, and they skeletonise leaves rather than chewing holes in them. Hall notes that sting toxicity increases with the size of the larva, so the large, fluffy autumn caterpillars are the ones that hurt most.
What does a puss caterpillar turn into?
A southern flannel moth. When fully grown, the caterpillar spins a tough cocoon about 1.3 to 2.0 cm (half to three quarters of an inch) long, with a small hump on top and a hinged lid, the operculum, that gives the species its name. The moth pushes this trap door open to emerge. Adults have a wingspan of 2.4 to 3.6 cm (about 1 to 1.5 inches), yellow to orange fur and black “boots” on their legs. Texas Parks and Wildlife notes the adults do not feed and die within about a week, and their long hairs are harmless. The cocoons are extremely tough, persist on trees long after the moth has left, and can even be found on buildings.
In what states are puss caterpillars found?
UF/IFAS gives the range as New Jersey to Florida and west to Arkansas and Texas, adding that the species is common in Florida but reaches its greatest abundance in Texas, from Dallas southward. A Baylor College of Medicine study of 188 sting reports found cases largely in Texas, Louisiana and Florida.
Our analysis of iNaturalist records agrees, with one twist: per 10,000 observations, Louisiana records the species almost twice as often as Texas. The records include adult moths as well as caterpillars, and reflect where people photograph them, not sting rates.
When puss caterpillars are around
The southern flannel moth has two broods a year in the South, with a possible partial third in the Deep South. UF/IFAS describes a spring and an autumn generation in Florida; Texas A&M says one to two generations occur, with caterpillars more common in the autumn. Autumn caterpillars overwinter inside the cocoon and pupate the following spring.
Sting reports follow the same two peaks. Texas poison centres logged 3,484 puss caterpillar stings from 2000 to 2016, with 12 per cent in July and 59 per cent in October and November. The Baylor study put peak months at July through November. Our iNaturalist index shows the same pattern: a July rise, then the highest share of records in October and November, while the saddleback caterpillar peaks earlier, in August and September.
How venomous is a puss caterpillar?
Very, for a caterpillar. UF/IFAS calls it one of the most venomous caterpillars in the United States, and a 2019 Biology Letters study called it North America’s most venomous caterpillar. Each hollow spine has a venom gland at its base, and according to Hall even shed larval skins can sting. The venom is not well characterised, though laboratory work suggests it is protein based and can break down red blood cells.
What the sting feels like is consistent across sources. Texas A&M describes intense, throbbing pain within five minutes of contact, sometimes pain in the armpit after a sting on the arm, and red spots at the site. UF/IFAS adds that a red grid-like pattern matching the spines often appears, followed by swelling. Less often there are body-wide effects: headache, nausea, vomiting, fever, swollen lymph nodes, and rarely seizures, shock or breathing difficulty.
| What Texas poison centres recorded | Share of 3,484 stings |
|---|---|
| Sting happened at the patient’s own home | 91% |
| Managed without going to a healthcare facility | 89% |
| No effects, or at most minor ones | 93% |
| Any skin effect reported | 90% |
| Patient aged 20 or over | 56% |
Source: Forrester, Wilderness and Environmental Medicine 2018, Texas poison centre reports 2000 to 2016.
Sources disagree on how long it lasts. Texas A&M and the Merck Manual say pain usually subsides within an hour and the spots fade in a day. Kentucky warns of swelling that may last for days. Both can be true: reactions vary with the person, the size of the caterpillar and, as early researchers found, the thickness of the skin where it touched. If you are unsure what caused a sudden burning welt, our bite and sting identification guide explains why the mark alone is weak evidence.
Can a puss caterpillar kill you?
Deaths are not reported in any of the extension or medical sources we reviewed, and the Texas data show most stings stay minor. The real risk is an allergic or severe systemic reaction: Texas A&M lists shock and breathing difficulty among rarer symptoms and says to see a physician immediately for allergic reactions such as widespread itching or difficulty breathing, and to refer eye injuries to a specialist straight away.
What do you do if you get stung by a puss caterpillar?
Call Poison Help on 1-800-222-1222 for advice on your symptoms, and get medical help at once for any breathing difficulty, widespread hives or a sting near the eye. The first aid steps extension and medical sources describe are lifting embedded spines off the skin with sticky tape and applying an ice pack; the Merck Manual adds washing with soap and water. A Central Texas Poison Center review of 96 stings found that no treatment promptly relieved the pain, so do not expect a quick fix, and follow the poison specialist or your doctor on anything beyond that.
Can a puss caterpillar kill a cat or a dog?
There is no published record of it. The 2019 Biology Letters authors wrote that, to their knowledge, no recorded accounts of non-human animal stings exist, though dogs experimentally injected with venom extract showed raised blood pressure and breathing rate. The absence of reports is not proof that a sting is harmless to a pet, so if you think your dog or cat has touched or mouthed one, call your vet. Our guide to pest control that is safe around pets and children covers keeping treatments safe in shared yards.
What kills puss caterpillars?
Mostly their natural enemies. UF/IFAS says that in most years puss caterpillars are kept under control by natural enemies:
- Parasitic flies and wasps. At least four tachinid fly species and two ichneumonid wasps attack it. Studies found 20 per cent parasitism by tachinids in Galveston and 50 per cent by the wasp Lanugo retentor in New Orleans.
- Birds. Blue jays, great-tailed grackles and downy woodpeckers have been seen eating the pupae. When netting kept birds off live oaks at the Texas Medical Center in Houston, caterpillar numbers on netted trees rose more than 7,300 per cent.
- Lacewings and lizards. Lacewings have been seen feeding on eggs and young caterpillars, and anoles take pupae.
Spraying is rarely needed. Where caterpillars are abundant, UF/IFAS says Bacillus thuringiensis or insecticides recommended for other caterpillars should be effective, and Texas A&M lists residual products labelled for caterpillars on ornamental plants. Apply only products labelled for the plant and site, exactly as the label directs. A licensed professional is worth calling for large shade trees, where spraying a whole canopy is not a homeowner job. Our explainer on garden pest control covers why label rules matter around edible plants such as citrus.
For schools and playgrounds, Texas A&M suggests the best solution may simply be teaching children and staff what the caterpillars look like and not to touch them with bare hands. Our guide to pest control in schools and childcare covers how those programmes work. At home, wear gloves when raking leaves or pruning oaks and elms in late summer and autumn, and check tree trunks, fences and walls near play areas, since mature caterpillars wander before spinning cocoons.
Frequently asked questions
Are puss caterpillars poisonous to touch?
Yes, though venomous is the accurate word: the harm comes from spines that inject venom on contact, not from eating it. The soft outer hair is harmless, but hollow spines underneath break off in the skin. Extension entomologists at UF/IFAS say people often mistake them as safe to handle because they look furry. Any contact with bare skin can cause a painful sting.
Do puss caterpillars sting on purpose?
No. Texas Parks and Wildlife describes the sting as an involuntary defence that happens only when a person or a predator such as a raccoon or bird grabs or presses on the caterpillar, driving venom-filled spines into the skin. In Texas poison centre data, 91 per cent of stings happened at the patient’s own home, so the yard trees are where to look.
Is the southern flannel moth dangerous?
No. The adult moth’s long, fine hair is harmless, according to Texas Parks and Wildlife, and the adults do not feed and live only about a week. Only the caterpillar stage stings. The moths are small, with a wingspan of about 1 to 1.5 inches, and covered in orange to cream fur that looks far more alarming than it is.
When are puss caterpillars most common?
In autumn. There are two generations a year in the South, but Texas poison centres received 59 per cent of their puss caterpillar sting reports in October and November, with a smaller peak of 12 per cent in July. Texas A&M likewise says the caterpillars tend to be more common in the fall, when they are larger and their stings are worse.
Sources
- Hall, Puss Caterpillar (Larva), Southern Flannel Moth (Adult), Megalopyge opercularis, UF/IFAS Featured Creatures EENY-545 / EDIS IN976, revised 2022.
- Perry and Dale, Stinging and Venomous Caterpillars of the Southeast, UF/IFAS Extension SP107, 2018, reviewed 2024.
- Merchant, Asps and Other Stinging Caterpillars, Texas A&M AgriLife Extension, Insects in the City ENT-3010.
- Brown, Entomology Update: Stinging caterpillars, Texas A&M AgriLife Extension, 2013.
- Bessin, Stinging Caterpillars in Kentucky, University of Kentucky Entfact-003.
- NC State Extension, Saddleback Caterpillar.
- Texas Parks and Wildlife Magazine, Southern flannel moths start out as puss caterpillars.
- Forrester, Megalopyge opercularis caterpillar stings reported to Texas poison centers, Wilderness and Environmental Medicine 29(2), 2018.
- Eagleman, Envenomation by the asp caterpillar (Megalopyge opercularis), Clinical Toxicology 46, 2008.
- Hood, Egan and others, Human-mediated disturbance in multitrophic interactions results in outbreak levels of North America’s most venomous caterpillar, Biology Letters 15(9), 2019.
- Stipetic, Rosen and Borys, A retrospective analysis of 96 asp (Megalopyge opercularis) envenomations in Central Texas during 1996, Journal of Toxicology: Clinical Toxicology 37(4), 1999.
- Merck Manual Professional Edition, Puss Moth Caterpillar (Asp) Stings, 2025.
- The Pest Control Brief analysis of iNaturalist research-grade records, pulled October 2026.
