7 Stinging Caterpillars That Pack a Venomous Punch

Buck Moth caterpillar

You’ve kept the termites out and the ants in check. Even the wasps have been evicted. But there’s one insect pest many people overlook. One that can pose a just as painful, even mortal threat: These seven stinging caterpillars that pack a venomous punch.

The slow-moving, leaf-munching worms seem harmless enough beyond cutting holes in the leaves of your shrubs, but some of them carry a nasty sting. “What might be mild for one person might be life-threatening for another,” says entomologist Ric Bessin with the University of Kentucky Extension. 

In studying these peculiar caterpillars, Bessin has been stung twice. All it takes is brushing up against them. When stung, Bessin suffered mild irritation that built over time but wasn’t enough to interrupt his day. But for the kids or pets playing in your yard, it may be a different story. So just in case, here’s how to spot dangerous caterpillars and keep your yard safe from them, too.

Dr. Ric Bessin, Entomology Extension Professor at the University of Kentucky, checking some pepper plants at the UK Horticulture Research South Farm in Lexington, Ky.

Types of Stinging Caterpillars

These spiny, venomous caterpillars become adult moths, many with beautiful colorations. They come in bright green and yellows, even reds, browns, and blacks. They come covered in fur or in strange shapes. No matter their appearance, they have one thing in common: You don’t want to pick them up.

Stinging caterpillars thrive in a wide range of environments and vary widely in appearance across the country. The University of Florida Institute of Food and Agricultural Sciences lists six species living in the Southeast alone. Around Kentucky and the Southeast, there are probably a dozen total species, Bessin says.

His advice is don’t touch hairy caterpillars you can’t identify, especially if they’re brightly colored. “Just don’t pick up one you don’t recognize,” he says. Instead, if you find one on the willow tree next to the swing set or in the front driveway, use a stick or other object to move it to a safer location.

But if you want to know what you’re dealing with, here are the stinging caterpillars you’re most likely to see in the backyard.

Saddleback Caterpillar (Acharia stimulea)

The saddleback caterpillar sports a green saddle that makes it easy to spot.
Photo Credit: Judy Gallagher / Flickr / CC BY 2.0

The saddleback is the most well-known and easy-to-identify stinging caterpillar. Bessin says in Kentucky, they’re called packsaddle caterpillars. It’s one people recognize more often.

Appearance: It’s easy to see why they got the name. Small, brown, and hairy, a green shape across the top of its back looks like a saddle blanket, while a small brown circle directly in the middle of its back looks like a saddle.

Fully grown, the caterpillar’s body is stocky and a bit less than an inch long. Where not covered with the green “saddle blanket,” the caterpillar is brown.

Where to find them: According to the University of Florida, saddleback caterpillars range throughout the eastern half of the United States, from South Florida to Maine and from Virginia to western Nebraska.

What they eat: Some favorite foods include maples, hibiscus, and crape myrtle.

Toxin: Most stinging hairs are on horn-like formations on either end, with rows of more stinging hairs along either side. If stung, burning, inflammation, and red blanching may occur around the affected area, which can also become a rash or welts that swell and itch.

Puss Caterpillar (Megalopyge opercularis)

Photo Credit: Judy Gallagher / Flickr / CC BY 2.0

You could be forgiven for not recognizing a puss caterpillar as a caterpillar at all.

Appearance: Sometimes referred to as “Italian asp” or “woolly slug,” this caterpillar looks more like a furry mouse than the typical green, worm-like picture most people bring to mind when they think of a caterpillar. Completely covered with soft, brown, fur-like hairs, the puss caterpillar is stout-bodied, growing to about 1 inch long.

The hairs hide the caterpillar’s body, only identifying the rear end by tapering to a tail-like narrowness at the end.

Where to find them: Puss caterpillars are often found in great abundance in large areas south of Dallas and reach from Florida northwards to New Jersey and west from Florida to Arkansas and west Texas.

What they eat: They feed on lots of different plants but favor oaks and elms.

Toxin: Their spines are hollow with a toxin gland at the base. The larger the caterpillar is, the more toxic its sting.

Io Moth Caterpillar (Automeris io)

Photo Credit: Andy Reago & Chrissy McClarren / Wikimedia Commons / CC BY 2.0

Now this one fits the classical picture of a caterpillar to the T, even if it’s named for the moth it becomes.

Appearance: Io moth caterpillars are pale green with yellow-white and red stripes running down their sides. Its stinging organs are clustered on fleshy protrusions extending from the caterpillar’s back, usually yellow or green with black tips.

Where to find them: These caterpillars can generally be found in most parts of the country excluding states west of Idaho.

What they eat: Much like the Saddleback, io moth caterpillars feed on a wide variety of plants but prefer hibiscus, elms, maples, wisteria, and willows.

Toxin: If stung, a burning sensation begins after contact and may turn red and itchy.

Hag Moth Caterpillar (Phobetron pithecium)

Photo Credit: Jerry A. Payne / Wikimedia Commons / CC BY 3.0 US

Like the puss caterpillar, the hag caterpillar or hag moth caterpillar hardly looks like a caterpillar at all but more like a small, brown leaf.

Appearance: Also called the monkey slug, they’re light to dark brown. They have lateral spines that come in as many as nine pairs. Those spines, looking like disheveled hair, give the caterpillar its name, sharing it with its later form, the hag moth.

Where to find them: These monkey slugs can be found across the southeastern United States.

What they eat: They feed on woody plants, including oak, dogwood, and apple. 

Toxin: They have toxic glands at the base of their spines. If stung, symptoms can range from burning and stinging to itching, redness, and inflammation.

Buck Moth Caterpillar (Hemileuca maia)

Photo Credit: Judy Gallagher / Wikimedia Commons / CC BY 2.0

Buck moth caterpillars can be tricky to identify, with both a light form and a dark form.

Appearance: The latter is more common, the University of Florida says, appearing black with tiny white dots on the body. The light variety shows white with a reddish head, but both types have dark, lateral rows of stinging spines on their backs.

Where to find them: The buck moth caterpillar is usually found across the eastern U.S., from Maine to Florida, going as west as Wisconsin.

What they eat: You’ll find them munching on your oak and willow leaves and can reach 2.5 inches in length.

Toxin: This is one caterpillar you don’t want to be stung by. The spines break off into the skin, release the toxin and cause sudden stinging, redness, and swelling that can last from one day to more than a week.

White Flannel Moth Caterpillar (Norape ovina)

Photo Credit: Judy Gallagher / Flickr / CC BY 2.0

Now the white flannel moth caterpillar, commonly known as Hackberry Leafslug, looks like what you’d expect a stinging caterpillar to look like.

Appearance: Growing as long as 1.25 inches, it has a yellow body marked with a wide black stripe down its back, bordered with red at each end.

This is a caterpillar whose poisonous warnings are certainly on display: along that black stripe are yellow bunches that contain non-stinging long hairs and shorter stinging hairs.

Where to find them: White flannel moth caterpillars are most commonly found in the eastern and southern parts of the country.

What they eat: Favorite foods for the flannel moth caterpillar are beech, hackberry, honey locust, mimosa, and redbud.

Toxin: The fine long hairs of this caterpillar can have a stinging, burning sensation and leave a painful rash and swelling.

Spiny Oak-Slug Caterpillar (Euclea delphinii)

Photo Credit: Andy Reago & Chrissy McClarren / Wikimedia Commons / CC BY 2.0

The spiny oak slug is another species that uses its bold coloration for advertising its toxicity.

Appearance: They come in a range of colors “but can be identified by their oval, stout bodies and abundance of spines protruding from them,” UF-IFAS says. Rows of spine clusters also run down the caterpillar’s sides, with two to four large clusters of spines protruding from the rear.

And while they might be loud, they’re small. Spiny oak-slug caterpillars grow to just under 1 inch long.

Where to find them: Most commonly, these caterpillars are found in the eastern and southern states, reaching west through Nebraska.

What they eat: Feeding favorites include oak, willow, and cherry species.

Toxin: Luckily, that small package doesn’t hide a powerful sting. Their spines are hollow with a toxin gland at the base, and its sting is considered milder than others, with symptoms like a burning sensation, redness, and inflammation.

Do Caterpillars Sting or Bite?

Do they really sting? Well, kind of. While they don’t pack stingers like bees and wasps, you don’t want to reach out and pick them up.

Urticating hairs: Across the country, certain caterpillars are covered in hairs that act like miniature syringes, called urticating hairs. An article Bessin wrote for the University of Kentucky Extension explains that these quill-like hairs are connected to poison glands they use as defensive weapons. 

When the hairs break through the skin, the poison is released, and the unlucky person or animal on the receiving end has been “stung.” Bessin describes them as “hollow, venom-filled quills.”

Possible reactions: Reactions to that sting vary. A caterpillar sting can leave you with a mild itch to severe pain and swelling, blistering, dermatitis, and even intestinal problems.  Some of these urticating hairs Bessin has examined under a microscope have specific weak points to help them break off in the skin, slowly oozing out the poison.

Luckily, the caterpillars themselves are not aggressive, he says. They’re not out looking to come after you, and the danger is in accidentally grabbing one or brushing up against it while pruning your redbuds.

Children are at particular risk, though, says the Louisiana State University Extension. That’s because youngsters are attracted to the bright, unusual coloration, which warns of a painful sting.

First Aid for Caterpillar Stings

Unfortunately, there’s no easy, effective home remedy to calm a caterpillar sting, says Bessin’s article for the Kentucky Extension.

But that doesn’t mean there’s nothing you can do.  Bessin says to stick a piece of tape where you’ve been stung and peel it off. Hopefully, this will pull out any quills still stuck in your skin.

Wash the area thoroughly with soap and water, which may help remove some of the venom. Quickly applying an ice pack or baking soda may help reduce pain and swelling. Antihistamines, used mostly for bee and wasp stings, are usually ineffective with caterpillar stings.

People who are young, elderly, or have existing health concerns are more likely to suffer severe reaction symptoms, and if those symptoms persist or if an allergic reaction occurs, seek medical attention.

*This information is for educational use only.

How to Get Rid of Stinging Caterpillars

That’s a lot of little potential threats crawling among your oaks and redbuds. You may want to take action. Fortunately, stinging caterpillars don’t threaten your lawn or ornamental shrubbery unless you get a large population on a single plant that can eat its way through too much foliage.

Every few years or so, the populations wax and wane, Bessin says. So some years, you may not see them at all, and several years later, they may be all over the place. Heavy infestation can become a possibility when populations are high.

Should you find yourself overrun with the hairy creatures, control is pretty straightforward:

  • “If you’re seeing a lot, you may consider using a nice, friendly garden spray to get rid of them,” Bessin says. The Kentucky Extension article says to use sprays with bacillus thuringiensis or carbaryl, spraying the entire infested shrub or bush. There are even organic options for the earth-conscious homeowner, he says.

Sprays may be needed for buck moths, in particular, says LSU, since they tend to emerge in large numbers. But for other species, the LSU article says, control is “seldom needed except for knocking an occasional specimen to the ground and mashing it.”

FAQ About Venomous Caterpillars

How Can You Tell if a Caterpillar is Venomous?

Venomous caterpillars often use warning coloration, such as their bright colors and distinct markings. Exceptions include the hag moth caterpillar and the puss caterpillar, which have primarily brown hairs. 

Another thing to look for is the long urticating hairs along their spines that can carry the toxin that makes them venomous. Urticating hairs are like any other hair you’ll see on a caterpillar except for one big difference: They’re connected to a caterpillar’s poisonous glands. When contact happens, these hairs push into the skin, causing the toxin to release into the body.

What is the Most Venomous Caterpillar?

The most venomous caterpillar is the lonomia obliqua, more commonly known as the giant silkworm moth caterpillar. Primarily found in southern Brazil, these stinging larvae look and act the part of something deadly.

Their toxin, released from the urticating bristles, may cause severe damage:

• Burning sensation
• Pain, swelling, and redness
• Headache
• Nausea and vomiting
• Anemia
• Leukocytosis

These spiky giant silkworm moth caterpillars are not something to mess with.

Are Caterpillars Poisonous to Dogs?

Caterpillars can be poisonous to dogs if a pet were to try and eat one, or get stung by the bristles. The urticating hairs on a caterpillar that are poisonous to humans are also poisonous to dogs. Luckily, in most cases, the damage to dogs is not severe.

Stings: While a sting from a poisonous caterpillar may be fatal depending on how your dog reacts, a sting will more likely result in an allergic reaction or cause irritation on the skin beneath the fur.

Ingestion: Skin contact is possible, but a much more real concern is that your puppy would sniff, lick, or eat a caterpillar. The severity of the reaction will depend on the dog. As a general rule, try to keep your dogs away from eating any caterpillars.

Caterpillar Control

While stinging caterpillars won’t seek you out and rarely cause severe damage, they can still pack a venomous punch. The young, elderly, and those with pre-existing conditions are more at risk of severe reactions to these stings. For some, it isn’t worth the risk. Call a local pest control pro near you to handle any venomous caterpillar concerns.

Photo credit: Judy Gallagher / Flickr / CC BY 2.0

Derek Lacey

Formerly the agriculture writer for the Hendersonville Times-News, Derek Lacey’s articles have appeared in U.S. News & World Report, The Charlotte Observer, News & Observer, and The State. He has won 15 awards from the North Carolina Press Association and GateHouse Media, for pieces ranging from news features and investigative reporting to photography and multimedia projects.