The Carlisle Mosquito Online

Friday, November 5, 2004


Biodiversity Corner Woolly Bear

Name: The Woolly Bear caterpillar is the larval stage of the Isabella Tiger Moth, Isia isabella a.k.a. Pyrrharctia Isabella. Other common names for the caterpillar are the banded woolly bear, the fuzzy bear, the hedgehog caterpillar (because of the way it curls into a ball when disturbed), and in the southern U.S. it is called the woolly worm.

Woolly Bear (Photo by Kay Fairweather)

When and where seen: Jon Golden found the woolly bear at the back of his house on School Street on October 30. You are most likely to notice woolly bears in September and October when they crawl around looking for a sheltered place to spend the winter. Since they spend the winter as caterpillars, it is possible to see them later in the year.

Identification: The woolly bear caterpillar is about 2 inches long and has a dense covering of bristles. At the head and tail end the bristles are black, and in the center they are a reddish brown. The width of the bands of color varies. The woolly bear moves quite quickly — for a caterpillar — at a rate of about four feet per minute. If you touch one or pick one up, it will immediately curl up into a tight ball.

Other tiger moth caterpillars: The woolly bear is the best known of the tiger moth caterpillars. All are quite common in the fall; all will curl into a ball; and all of them are reasonably large and hairy. The 3 black and brown bands distinguish the woolly bear from the others. I found a giant leopard moth caterpillar this fall. Despite its name, it is also a member of the tiger moth family. The bristles are all black and when the caterpillar curls up you can see bright red bands between the body segments.

Food: Unlike some caterpillars that will eat only one species of plant, the woolly bear is not a picky eater. It will eat dandelion, plantain, nettles, and a whole variety of low-growing weeds and grasses.

Weather forecasting: According to folklore, the width of the brown band on the woolly bear is a predictor for severity of the upcoming winter — the wider the brown band, the more mild the winter. What really seems to be happening is that the color varies with the age of the caterpillar, so if the past winter was heavy and spring was late, the fall caterpillar would be younger and sporting different color patterns.

References: Peterson First Guides, Caterpillars, Amy Bartlett Wright; Stokes Nature Guides, A Guide to Observing Insect Lives, Donald W. Stokes; Farmers Almanac on the web at; Central Region HQ for the National Weather Service at

Submissions for the Biodiversity Corner are encouraged from everyone. Please feel free to write up any species that interests you. The only requirements are that it exists in the wild and was seen in Carlisle. You can also let me know what you've seen and I will write it up. Send your info to Kay Fairweather at 392 School Street, Carlisle MA 01741 or to

2004 The Carlisle Mosquito