The woolly bear caterpillar is the larva of the Isabella tiger moth (Pyrrharctia isabella), and no, it isn’t poisonous. It doesn’t sting either. The bristles carry no venom, although someone with sensitive skin might get a bit of an itch from holding one. It spends the winter frozen in leaf litter and turns into a pale orange moth the next spring.
Most people meet one in October, crossing a driveway on its way to somewhere sheltered for the winter. Several other fuzzy caterpillars are out at the same time, and a few of them do sting. So if the one in front of you isn’t clearly black at both ends and orange in the middle, identify garden pests from a photo with PlantIn before you pick it up. As for the old idea that the bands predict the winter, it doesn’t hold up.
Quick Facts About the Woolly Bear Caterpillar
| Fact | Details |
| Scientific name | Pyrrharctia isabella (family Erebidae, tiger moths) |
| Also called | Banded woolly bear, woolly worm |
| Size | A little over 2.5 cm (1 in) when fully grown |
| Look | Stiff bristles, black at both ends, rusty orange in the middle |
| Found | Across the United States and Canada |
| Eats | Plantain, dandelion, dock, aster, goldenrod, nettles, grasses |
| Stings? | No. Bristles are not venomous |
| Winters as | A caterpillar, frozen under bark, logs or leaf litter |
| Becomes | Isabella tiger moth, wingspan 3.8–5 cm (1.5–2 in) |
Banded Woolly Bear Caterpillar Identification
Look for black at both ends and a rusty orange band in the middle, spread over 13 body segments. A grown one is just over 2.5 cm long. Run a finger along it and the bristles feel stiff and even, closer to a bottle brush than to fur, with no tufts or long hair pencils sticking out. Remember that last part. The fuzzy caterpillars that do sting tend to have tufts.
Touch one and it curls into a ball and goes still. It’s slippery like that, and surprisingly hard to pick up.
Colors vary a lot. Siblings from one egg batch can look noticeably different, and every caterpillar loses some black and gains orange each time it molts, six times in all. A small, mostly black one in early autumn is usually just young. The bands tell you about age and species, nothing about the weather.
Yellow, Black, Brown or White Woolly Bear Caterpillar: Which One Is It?
“Woolly bear” gets used for several hairy tiger moth caterpillars, and North America has around 250 tiger moth species, so it isn’t a precise name. A banded one and an all-brown one are often the same species at different ages. Yellow or white usually means something else.
| What you see | Most likely species | Notes |
| Black ends, rusty middle | Banded woolly bear caterpillar (Pyrrharctia isabella) | The one in the folklore |
| All rusty brown or orange | Older banded woolly bear | The black shrinks with each molt |
| Yellow, cream or pale brown, softer and longer hair | Yellow woolly bear (Spilosoma virginica) | Becomes the white Virginian tiger moth |
| White | Pale yellow woolly bear, or a hickory tussock moth (see below) | Check for black tufts |
| Glossy black bristles, up to 7.5 cm (3 in), red rings when it curls | Giant leopard moth (Hypercompe scribonia) | Sometimes called the giant woolly bear caterpillar. Doesn’t sting |
| Black-brown, in Greenland or the Canadian Arctic | Arctic woolly bear (Gynaephora groenlandica) | Takes years to mature |
Giant Leopard Moth Caterpillar vs Woolly Bear
Size gives it away. A giant leopard moth caterpillar can reach 7.5 cm, about three times the length of a banded woolly bear, and it’s glossy black from end to end. When it curls up you’ll see thin red rings between the segments. The banded woolly bear is duller and always has some orange in the middle. Neither one stings, and you’ll find both tucked under flower pots or firewood in winter.
Yellow Woolly Bear Caterpillar
This is the one gardeners actually complain about. The yellow woolly bear (Spilosoma virginica) has two or three generations a year and doesn’t stick to weeds: Utah State Extension lists hemp and many vegetable crops among its food. If you’re finding holes in vegetable leaves, turn the leaves over before you blame a disease. It winters as a pupa in soil debris, so you won’t see it crawling around in October.
Is the Woolly Bear Caterpillar Poisonous?
No. There’s no venom, and the bristles aren’t urticating, meaning they don’t snap off in your skin and release irritants the way stinging caterpillar hairs do. Kids have been picking these up for generations.
Two small caveats. The bristles can cause dermatitis in some people, usually a short itch or a little redness where they pressed in. Cornell’s IPM program also says loose caterpillar hairs can set off asthma, especially in children, so wash your hands afterwards and keep one away from a child’s face.
Why People Think the Woolly Bear Caterpillar Stings
Most of the time it was a different caterpillar. Before you pick up anything fuzzy, rule out these:
- Hickory tussock moth caterpillar: mostly white with black markings and a few long black hair pencils. Usually on hickory and walnut.
- White-marked tussock moth caterpillar: bright red head, yellow-and-black stripes, upright yellow or white tufts on the back.
- Saddleback, stinging rose and io moth caterpillars: smooth-bodied, with branching spines instead of fur.
Their stings leave a burning rash that can last more than a week. Press packing tape onto the spot and pull it off to lift out the hairs. Then wash the skin and treat it like any insect sting, and get medical help if the swelling spreads or breathing changes.
Is a Woolly Bear Caterpillar Poisonous to Dogs and Cats?
Not toxic, but chewing one is unpleasant for the animal. The ASPCA says swallowed caterpillar hairs can irritate a pet’s lips, mouth and throat, and lists head shaking, pawing at the mouth, vomiting and diarrhea as typical signs. It isn’t considered life-threatening.
Call your vet or the ASPCA Animal Poison Control Center (888-426-4435) if symptoms go on for more than a few hours, the face swells, or you’re not sure which caterpillar your pet found.
What Does a Woolly Bear Caterpillar Eat?
Weeds, mostly. NC State Extension’s banded woollybear fact sheet lists plantain, dandelion, dock, aster, goldenrod and some grasses, and the National Weather Service adds nettles. They feed during the day and stay low, on plants close to the ground rather than up in shrubs.
None of that is a crop, which is why NC State tells people not to spray for them.
Curious what yours was eating? You can identify the weed it was eating from a photo in the PlantIn app. Often it’s broadleaf plantain.
Woolly Bear Caterpillar Winter Prediction: Does It Work?
It doesn’t. Band width depends on how old the caterpillar is, how long it has been feeding and which species it is, so it describes the summer that just ended. The National Weather Service’s woolly bear winter forecast explainer comes to the same conclusion.
The folklore goes like this: wide black ends mean a long, hard winter, and a wide orange middle means a mild one. Some people read the 13 segments as the 13 weeks of winter, with a dark head end meaning a cold start.
Science got involved in 1948, sort of. Dr. Howard Curran, curator of insects at the American Museum of Natural History, went up to Bear Mountain, New York, and looked at 15 caterpillars. A reporter came along, the New York Herald Tribune ran the story, and Curran kept counting for about eight years. Fifteen caterpillars from one hill can’t say much about a continent’s weather.
Because the orange band widens with every molt, a well-fed caterpillar late in the season will always look like a mild-winter forecast. Banner Elk, North Carolina, holds its Woolly Worm Festival every October anyway.
How the Woolly Bear Caterpillar Survives Freezing
It freezes. Once it has settled under bark, a log, a stone or deep leaf litter, it starts making glycerol, a natural antifreeze, and ice forms between its cells but not inside them. The heart stops first, then the gut, then the blood. NC State and the National Weather Service both give its limit as around -68 °C (-90 °F). In spring it thaws and starts eating again.
The bristles don’t keep it warm, by the way. They seem to help it freeze in a more controlled way.
What Does a Woolly Bear Caterpillar Turn Into?
The Isabella tiger moth. It’s a plain thing, yellow-orange to buff with a few small black spots and a wingspan of 3.8–5 cm, and it flies at night, so most people never connect it with the caterpillar. Females have pinkish hind wings. The moth comes out about two weeks after the caterpillar pupates in spring.
Woolly Bear Caterpillar Life Cycle
- Eggs, laid in batches of 100 or more on weeds, grasses and trees.
- Caterpillar. It molts six times and ends up just over 2.5 cm long.
- Winter, spent frozen in a sheltered spot. North Carolina gets one or two generations a year, so a caterpillar you find in spring might be a moth by summer.
- Cocoon. In spring it eats a little, then spins a loose cocoon with its own bristles woven in. That’s the fuzzy cocoon people find under boards and pots.
- Moth, about two weeks later.
Arctic Woolly Bear Caterpillar
This is a different species (Gynaephora groenlandica) from Greenland and the Canadian Arctic, and its summers are short. It can only feed for a few weeks after the snow melts, so it takes about seven years to get big enough to pupate. You’ll still see “14 years” quoted online. That number traces back to an older study, and current references put it at around seven. In winter it survives down to about -70 °C.
How to Care for a Woolly Bear Caterpillar You Found in the Fall
Usually the best thing is to put it back where it was going: a leaf pile, the base of a hedge, under a log. A woolly bear crossing the path in October has finished eating and is looking for a place to freeze. A warm house gets in the way of that.
If your kid wants to watch it turn into a moth, though, it’s doable.
- Get a plastic tub with a few small air holes, put a paper towel on the bottom, and add some twigs and dry leaves to hide under.
- Give it fresh plantain or dandelion leaves every day. A summer caterpillar that’s still growing may need them twice a day. It gets its water from the leaves, so skip the dish and lightly mist one leaf instead.
- Over winter, keep the tub somewhere cold but sheltered, like an unheated shed or garage. Autumn caterpillars need that chill before they’ll pupate.
- In spring, bring it back into the light, offer food again and wait for the cocoon.
- Let the moth go at dusk, near where you found the caterpillar.
FAQ
Can You Touch a Woolly Bear Caterpillar?
Yes, gently. Banded woolly bears don’t sting or bite and have no venom. Expect it to roll into a ball on your palm. If your skin is sensitive you might itch a little, so wash your hands after and don’t rub your eyes. Leave white caterpillars with black tufts alone until you’re sure it isn’t a hickory tussock moth.
Is a Woolly Bear Caterpillar Dangerous?
Not really, to people or pets. It has no venom and doesn’t sting. The bristles can make sensitive skin itch or irritate a pet’s mouth, and loose hairs can trigger asthma in some people. The bigger risk is picking up a stinging tussock moth caterpillar because you thought it was a woolly bear.
What Does an All Black Woolly Bear Caterpillar Mean?
Most likely it’s a young banded woolly bear that hasn’t molted much yet. The other common option is a giant leopard moth caterpillar: glossier, up to 7.5 cm long, with red rings between the segments that show when it curls. Neither tells you anything about the coming winter.
How Long Do Woolly Bear Caterpillars Live?
A banded woolly bear that hatches in late summer stays a caterpillar for roughly eight months, frozen for most of it. The pupa stage takes about two weeks, and then the moth flies through the summer. Arctic woolly bears are the exception, at around seven years as caterpillars.
Do Woolly Bears Eat Garden Plants?
The banded one mostly eats weeds like plantain, dandelion and dock, so damage worth worrying about is rare. The yellow woolly bear will chew vegetable leaves. Picking them off by hand is enough for either, and NC State advises against insecticides for banded woolly bears.
