Frost on the pumpkin, honking geese overhead, and a forest full of skeletal trees -- fall has come, and winter's closing in.
An equally reliable sign of seasonal change is the intermittent parade of woolly bears that marches along and across country roads. It begins in September and continues until consistently cold weather settles in. Some days I see dozens of woolly bears, all on their way to some secret hideaway that even they don't understand. Driven by changing photoperiod -- shorter days -- which in turn directs their hormones and instincts, they're searching for winter shelter. They may find it under a tuft of grass, beneath a pile of leaves, in a hollow log or under a rock. There they curl into a ball and while away the winter as caterpillars.
Driven by hunger: Come spring, woolly bears leave their shelter and, driven now by hunger, gorge on dandelions, pig's ears, and grasses. Then they spin a silky cocoon and begin the fascinating transformation from caterpillar into moth. In late May adult Isabella tiger moths emerge.
Compared to its well known larval counterpart, the Isabella moth is nondescript and unknown to most naturalists. They mature quickly and spawn a summer brood of woolly bears. It is these subsequent summer moths that lay the eggs that become the caterpillars we see each fall. Hence, Isabella tiger moths breed twice a year.
Fascinating as the natural history of woolly bears may be, it is their alleged weather forecasting skills that captures the imagination. Woolly bears are easily recognized. They are about two inches long, hairy and black with a rust-colored band encircling the midsection.
It is the rusty band that tells the tale. Folklore has it that the width of the rusty band can predict the severity of the coming winter. The narrower the rusty band, and hence the blacker the woolly bear, the more severe the coming winter will be.
And don't be fooled by the all black caterpillars of the giant leopard moth. They behave much like a woolly bear, but are a completely different critter. Examine one closely, and you'll see bright red bands between its body segments.
Not so: As far as the weather forecasting ability of woolly bears is concerned, it's just not so. Woolly bears do not predict the weather. They react to it. It is their physiological and anatomical reactions that probably gave rise to this bit of folklore.
A woolly bear's rusty ban widens with age. Each time the caterpillar molts, it emerges with a wider rusty band. Unseasonably cold fall mornings send younger individuals scurrying in search of winter shelter. So off they go, through woods and fields, across roads and highways. Older, rustier caterpillars, meanwhile, have already retired for the winter. That's why we see so many mostly black woolly bears on chilly mornings. It is not unreasonable that someone somewhere made the connection between woolly bears with narrow rusty bands and cold weather. Throw in a coincidentally bad winter or two, and I'm sure it didn't take long for woolly bears with narrow rusty bands to become associated with hard winters.
Current reflection: In truth, though, what we see reflects current conditions, not a prediction for the future. Heck, professional meteorologists have a hard time nailing a five-day forecast; why should we expect better from a lowly caterpillar?
The woolly bear gets its name from the long hairs that cover its body. But the covering is far from woolly. The hairs are short, stiff and bristly. They help protect the fleshy caterpillar from predators. Many predators avoid bristly, irritating food items. When a woolly bear is disturbed, it simply curls up into a ball -- a seemingly lifeless fuzzball.
Few charades are foolproof, however. Skunks roll woolly bears around on the ground until the hairs fall off. And birds such as orioles, tanagers, and cuckoos whack hairy caterpillars on a branch to remove the bristly hairs.
If you find a woolly bear this week, examine it carefully. If its rusty band is narrow, the caterpillar is relatively young. And the coming winter? Your guess is as good as the woolly bear's.