Woolly Bears, also called Woolly Worms are a commonly seen caterpillar of the Isabella Tiger Moth (Pyrrharctia Isabella). They are quite common from northern Mexico throughout the United States and across southern Canada.
You can often see them in the fall slowly traveling along the ground seeking out a place to spend the winter. If you pick one up, they will curl up and play dead. Distinctive banding of reddish-brown adorns their bristly body. Woolly bears do not actually feel like wool but they are covered with short, stiff bristles of hair. Beware because the hairs of this caterpillar may cause dermatitis to some people.
Some say that the woolly bear’s banding helps forecast the winter weather but most scientists discount this as folklore. According to legend, the wider its middle brown section is the milder the coming winter will be. A narrow brown band is said to predict a harsh winter.
Color variations are due to many factors though including the caterpillar’s age. The older the larvae the more reddish hairs are present; therefore they have less brown or black hairs on the ends. As larvae they consume a varied diet of plants and are found in most areas where there are plants to consume.
Northern areas usually have two generations a year, but southern areas may have three or four generations. The first generation of eggs hatches into caterpillars in the spring. During the summer they feed and grow and then spin a brown cocoon. Pupation lasts for 2 to 3 weeks, when the adult Isabella Tiger Moth emerges to mate and lay eggs. Eggs that hatch at the end of summer feed and grow during the fall, then find a place to overwinter in the leaf litter. Overwintering as a caterpillar in leaf litter, these insects have the ability to produce a cryoprotectant (antifreeze) which permeates their cells and keeps them from freezing. In the spring they emerge as adults and the cycle continues.
The adult is a medium-size moth, with yellowish-orange and cream-colored wings with small dark spots.
Woolly bears came to notoriety when in the fall of 1948, Dr. C. H. Curran, curator of insects at the American Museum of Natural History in New York City, went to Bear Mountain State Park, NY, to study woolly bear caterpillars. He collected as many caterpillars as he could in a day, determined the average number of reddish-brown segments, and then forecast the coming winter weather. Dr. Curran's experiment, which he continued over the next eight years, attempted to prove scientifically a weather rule of thumb. The resulting publicity made the woolly bear the most recognizable caterpillar in North America.
Woolleybear Festivals are held in various locations in the fall across the nation including two places right here in Pennsylvania. One has been held yearly in early fall since 1997 in Lewisburg, Union County. It features crafts for kids, food, games, a pet parade, and a "Weather Prognostication Ceremony." Also in Oil City, Venango County, the Woolley Bear Jamboree, begun in 2008, features "Oil Valley Vick" to predict the winter weather.