Black and Brown Caterpillar: The Woolly Bear, Identified

A fuzzy caterpillar that is black at both ends and rusty brown in the middle is, in North America, almost always the banded woolly bear (*Pyrrharctia isabella*). NC State Extension describes mature caterpillars as a little over an inch long and covered in stiff hairs, with rusty-red hairs in the middle of the body and black hairs at either end; the National Weather Service gives about 1 1/2 inches. When disturbed it commonly rolls into a ball (Missouri Department of Conservation).

It turns into the Isabella tiger moth, which the Missouri Department of Conservation describes as having a 1 3/4 to 2 1/4 inch wingspan and yellow or tan forewings with faint lines and small dark spots; females have orange hindwings.

The banded woolly bear is not one of the stinging caterpillars. NC State Extension calls it virtually harmless to people. The Missouri Department of Conservation adds a caution: contact with the bristles can cause dermatitis in some people, although most people have no reaction, and sensitivity varies between people and between caterpillars.

The practical rule is to move it with a leaf or stick, or wear gloves, rather than pick it up bare-handed, and to wash your hands afterwards. Be more careful with any caterpillar you are not sure about: the southern flannel moth caterpillar, which can be reddish-brown and looks like a tuft of cotton or fur, has venomous hairs (Texas A&M). If a rash, pain or swelling follows contact with any caterpillar, see a clinician; in the United States Poison Help on 1-800-222-1222 can advise.

• Garden tiger (UK and Europe, also called woolly bear): up to 6 cm, mostly black and ginger with longer white hairs (Wildlife Trusts)
• Brown-tail (UK): black with long brown hairs, two red spots and white marks along the sides, found in conspicuous communal webs; its hairs cause skin irritation (Wildlife Trusts)
• Knot grass (UK): black with brown hairs and a row of alternating red spots and lines along the top (Wildlife Trusts)
• Southern flannel moth caterpillar (southern US): teardrop-shaped, silky hairs like cotton, yellow or grey to reddish-brown; a stinging caterpillar (Texas A&M)
• Fall webworm (North America): caterpillars living together in webs at the ends of branches, active later in summer and into fall (University of Maryland Extension)

A lone caterpillar with clean black ends and a rusty middle, walking across a path in autumn, is most likely the woolly bear. A caterpillar in a communal web, with tufts, or looking like a cotton ball is something else, and should not be handled. See the caterpillar varieties page for more.

No. The folklore holds that the longer the black bands, the longer and harsher the winter, and that a wide brown middle band means a mild one. The National Weather Service traces the legend's popularity to Dr. Howard Curran, who in 1948 counted the brown bands on 15 caterpillars at Bear Mountain, New York, and made a winter prediction. Some forecasters also link the caterpillar's 13 body segments to the 13 weeks of winter.

The National Weather Service's verdict is that the colouring depends on how long the caterpillar has been feeding, its age and its species, so it reflects the current or past season's growth, not the coming winter. NC State Extension explains the mechanism: as the caterpillars grow, black hairs are replaced by orange ones, so the rusty band is widest in mature caterpillars. A wide band means an older caterpillar. The Missouri Department of Conservation likewise says the prediction has no scientific basis.

Woolly bears eat low plants, including many weeds. NC State Extension lists plantain, dandelion, dock, aster, goldenrod and some grasses; the Missouri Department of Conservation adds maple and elm, sunflowers and clovers. There are one or two generations a year in North Carolina and two broods in Missouri.

The caterpillars people notice crossing roads and paths in autumn are often full-grown larvae looking for a place to spend the winter; the Missouri Department of Conservation says the species overwinters as full-grown caterpillars. They withstanding freezing temperatures down to -90 °F according to NC State, with glycerol acting as a natural antifreeze (Newlin Grist Mill). In spring they pupate in a cocoon made from their own hairs and emerge as moths (Missouri Department of Conservation).

Nothing, in most cases. NC State Extension points out that because woolly bears are virtually harmless, feed on weeds and are important in folklore, it would not make sense to apply an insecticide for their control. If one is in the way, move it with a leaf into leaf litter or under a shrub, where it can find shelter for the winter. To confirm the species, photograph it from above and the side; photograph it and the app identifies it.

Research and drafting for this page used AI assistance. Every figure, date and quotation was then checked line by line against the sources listed at the bottom of the page, each of which was opened while writing. Nothing here is a diagnosis. If a bite, sting or contact with an insect is followed by trouble breathing, swelling of the face or throat, spreading redness, fever or any symptom that worries you, get medical care; in the United States Poison Help (1-800-222-1222) is free and open 24 hours a day.