Featured Poison

Puss Moth Caterpillar: It’s Cute, Furry, and Venomous

An internet friend of mine regaled me with a tale of a buddy of his that looked like he got whacked in the face with a 2 x 4. Did he owe money to a bookie? Girlfriend beat him up? No, he got his ass handed to him by a one inch long fluffy little caterpillar. The hell you say? Yeah, a caterpillar. What’s the world coming to? Every day that I step outside I feel like I’m in Nature’s Thunderdome with Tina Turner as ringmaster.

Puss moth caterpillar by Valerie Bugh

Puss moth caterpillar by Valerie Bugh (c) (AustinBug.com)

This cute little fella, Megalopyge opercularis (left), goes by the name puss, tree asp, or southern flannel moth caterpillar. Their habitat starts in Maryland and sweeps down south to Florida and west into Texas and Missouri, inhabiting all the states in-between. It resembles a Tribble, and if you’re an original Star Trek fan, you’ll notice the resemblance, too. But while Tribbles were relatively harmless, save for the exponential reproduction, the puss caterpillar is venomous. Buried beneath its hairs, our furry friend has 6 rows of urticating hairs. These specialized hairs are like mini-hypodermic needles hooked up to glands full of venom that inject upon contact.

The caterpillars emerge from their cocoons in the spring, and grow and darken in color as they consume the foliage around them. As the spring-time caterpillars turn into moths, those too will lay eggs, giving rise to a second generation. Thus the prime time for envenomations is the early summer and early fall (1).

Historically, the puss moth caterpillar has been an ongoing problem in many areas, and particularly Texas. A 1923 circular from the U.S. Department of Agriculture (2) reported that thousands of stings have occurred in a single season, and that “in some cases the fear of the caterpillars became almost a mania.” And in 1921 schools in San Antonio were shut down until they could get the caterpillar population under control. The best quote from the circular, however, is:

In Dallas and Fort Worth, Tex., and other cities the forestry departments were deluged with requests that something be done to eliminate the pest, and the street trees were sprayed with arsenicals on an extensive scale.

The saying “if you can’t beat them, join them” obviously doesn’t apply in Texas, instead it’s arsenic warfare. I shouldn’t be so hard on Texas, it was the ’20s after all, and arsenic was a popular and common pesticide….and murder weapon, but we’ll leave that for a later date.

The most common places to be stung are the hands, arms, and feet, with symptoms of envenomation ranging from painful to severe. Pain is obviously the first and most common symptom, but can also include swelling, nausea, headache, chest pain, and shortness of breath (3). In more serious cases, shock-like symptoms and seizures occur, requiring hospitalization (3). Treatment of non-life threatening  stings is usually just supportive, with anti-histamines, such as cimetidine (Tagamet) (4), and/or methylprednisone for inflammation, pain relievers for the pain, and benzodiazepines to calm the nerves (5). If you’re in shock or having a seizure, you should probably stop reading now and get some real help.

The unfortunate part, at least for me, is that not a lot of study has gone into identifying the exact nature of the puss moth caterpillar venom. But this is typical for many venomous species. The fact is, venom is not just one chemical substance, it is usually made up of dozens of compounds. These can range from acetylcholinesterases to paralyze, to disintigrens to prevent blood coagulation, to toxins causing death.

Puss moth caterpillar by Valerie Bugh (c) (AustinBug.com)

Puss moth caterpillar by Valerie Bugh (c) (AustinBug.com)

Death? Not likely from this furry creature, but it will hurt. A lot. The best way to prevent being stung by one is to avoid it, which is easier said than done. My girls love caterpillars – my oldest even kept one as a pet in her room, until her mother found out. So it’s the kids I worry about. Who wouldn’t want to pick up and pet a furry caterpillar? But if you do get stung the best course of action – in a non-emergency – is to make sure you remove the hairs, as they can be transferred to other parts of your body. Scotch tape would work well for removing the hairs, followed by a dose of anti-histamine and some topical hydrocortisone  . . . followed by some real Scotch.

So be safe, be smart, and for goodness sake, don’t go petting any strange caterpillars.

*** Featured image of Megalopyge opercularis by Valerie Bugh © (www.austinbug.com) used with permission ***

1. Eagleman, David M. “Envenomation by the Asp Caterpillar (Megalopyge opercularis).” Clinical Toxicology 46.3 (2008): 201-05.
2. Unites States. Department of Agriculture. Department Circular 288. The Puss Caterpillar and the Effects of Its Sting on Man. By F. C. Bishopp. N.p.: n.p., 1923.
3. Mcgovern, J. P., G. D. Barkin, T. R. Mcelhenney, and R. Wende. “Megalopyge Opercularis: Observations of Its Life History, Natural History of Its Sting in Man, and Report of an Epidemic.” JAMA: The Journal of the American Medical Association 175.13 (1961): 1155-158.
4. Pinson, Robert T., and James Alan Morgan. “Envenomation by the Puss Caterpillar (Megalopyge Opercularis).” Annals of Emergency Medicine20.5 (1991): 562-64.
5. Holland, Daniel L., and David R. Adams. ““Puss Caterpillar” Envenomation: A Report from North Carolina.” Wilderness & Environmental Medicine 9.4 (1998): 213-16.

18 thoughts on “Puss Moth Caterpillar: It’s Cute, Furry, and Venomous

  1. I got itching stings/nettle-like rashes on my arms and neck from cutting overgrown foliage here in Florida, this happened couple times before I realized it was from innocently-looking caterpillars with venom spikes. It was a different species – they were green with yellow and orange dots and only few clumps of spikes, much less fuzzy than this one

    • Something from the Lonomia genus? Seems like every day since I moved to the south I see a bug I’ve never seen before. Sucks for me to be allergic to insect bites.

      • I am not expert, I don’t know. Nasty stinging caterpillars came to me as a total surprise – I grew up in Prague and lived in San Francisco Bay area, most caterpillars there are quite innocuous, as a kid I used to pick them all the time.

  2. i just found one of these on my neck when I brushed it of it started burning like a match. I got nauseous from it and took some Benadryl and feel better. Kinda scarry, is this an actual moth that will fly someday?

    • I’m a live and let live type of person, so I’d put it back, being careful not to touch it. Take it to another area, maybe your neighbors yard 🙂

  3. Wish you had a page with an index of topics? Please, o please? Thanks, great science writing, wonderful wit, solid research…how refreshing!

  4. A few summers back, I was trimming my yard (Texas), stuck my leg into a bush and got a whole mob of these dang things on my shin. Felt like someone was holding a hot iron to my leg. I could feel the venom traveling up my body as successive lymph nodes began to ache. Went to an emergency clinic, they said go home and weather it and billed me $800. Took forever for the pain(s, the bill hurt horribly) to fade and the red marks lasted for weeks.
    Lesson: wear long pants. If they’re dropping outta the trees, like they were known to do here back in the 20s, carry an umbrella. It’ll protect you from melanoma anyway. (Oh snap, too late….)

  5. I don’t think you mean cimetidine to use for treatment I think you mean loratadine, that is an antihistamine not cimetidine

  6. I was out front eating my doughnut when I saw one crawling on my tree. Went for closer look and saw several more of them monsters. Making mental note to watch where I put my hands. Thanks for the informative and fun article. 👍

  7. Just got stung by one of these a day ago. The pain was comparable to a bee sting, with persistent tingling in my entire leg. A tender 1″ diameter rash remains 1 day later. In my case the pain was not too terrible. I’d say 3/10, not bad enough to keep me up at night

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