Illustration by Adelaide Tyrol
I once had a college professor who said he could predict the weather by playing woolly bears like dice. He would pick up a woolly bear, which immediately curled up, then shake the fuzz-ball, blow on it, and roll it onto the ground. If the woolly uncurled and crept east or west, an average winter was coming. When it crawled north, mild weather lay ahead. But if it headed south, beware!
Across its vast range, which stretches from northern Mexico throughout the lower 48 states and up into southern Canada, myths are based on the three bands of a woolly’s coat. Some say that a wide middle band is a harbinger of a mild winter. Others insist that if the black band in front is longer than the one in the rear, the early part of the coming winter will be more harsh, and vice versa. There’s even a story that the number of body segments covered with black fuzz foretells the number of hard winter months ahead.
In truth, the woolly bear’s stripes paint a picture of weather past. There are 13 segments to a woolly bear’s body: the front four to five segments are black, the middle four to six are reddish-brown, and the rear two to three segments are also black. Occasionally, all-black woollies have been found.
The woolly bear’s reddish-brown band grows faster than the black bands on each end as the caterpillar ages. During mild autumn weather, the tawny middle grows quite wide before the larvae enter winter dormancy. Wide middle bands seen in autumn, therefore, and in the following spring, are evidence of a lingering fall. During a cool autumn, however, woolly bears grow slowly, so the black bands tend to remain wider. If woolly bears are forced to hibernate when their black bands are still quite wide, it’s because an early winter came along. Woolly bears found in the spring with narrow middle bands are a reminder that the past winter came early.
Why bear wool at all? A woolly’s stiff bristles do not sting, nor is its body poisonous. But bristly hairs cause discomfort as they build up in the stomach linings of birds. Our native cuckoos are among the few local birds that can eat woolly bears and other hairy caterpillars. Over time, as a cuckoo’s stomach becomes felted with caterpillar hairs, it sheds the stomach lining and grows a new one. This past spring and summer, when we were invaded by hoards of hairy tent caterpillars, the call of the black-billed cuckoo was common as they feasted. Other birds that feed on hairy caterpillars may also eat woolly bears include: gray catbirds, American crows, rufous-sided towhees, and brown thrashers. Certain mammals may also partake, including deer mice, raccoons, coyotes, striped skunks, and red foxes.
Woolly bears feed in old fields, roadsides, pastures, and meadows. Although they prefer plantains, dandelions, and grasses, they will consume campions, clovers, asters, and other flowers. Woollies eat the lower leaves and do little or no damage to gardens and ornamentals. “The caterpillars do eat elms, maples, birches, sunflowers, and other species,” says Donald Lewis, extension entomologist for Ohio State University and an expert on woollies, “but their population is never large enough to have a significant impact on foliage. And there aren’t enough of them to have a big effect on nutrient cycling as they convert leaves into droppings.”
The woollies we see in autumn are the summer’s second generation. Caterpillars emerge in April or May, feed, and then spin a brown cocoon of silk into which they weave a soft felt made of their own hairs. Cocoons are located in deeply furrowed tree bark, in rock crevices, and beneath stones. After pupating two weeks, an Isabella tiger moth emerges from the cocoon. Female Isabellas have orange-tinted wings, while the males’ wings are tan. The abdomen is covered with a tawny felt bearing three rows of black spots.
Fertilized females lay pale yellow eggs on the leaves of plants that will make good food for the larvae. Eggs hatch a week later. Caterpillars molt about six times as they grow. With each new instar, the brownish, middle band widens. When this first generation of larvae mature, they pupate, transform into adult moths, and lay the eggs that will hatch into the crop of late-summer woollies.
When autumn arrives, woolly bears scurry in search of a cozy place to overwinter, favoring the shelter beneath leaves and under rocks and logs. Concentrated proteins and sugars in their body fluids form an antifreeze so effective that a caterpillar can survive even encased in ice. But be careful if you discover an overwintering woolly bear – the heat from your hand can cause it to thaw and awaken, at its peril.
Michael Caduto is an author, storyteller, educator, and ecologist living in Chester, Vermont.