Finding a banded woolly bear caterpillar during a walk in the woods leaves no doubt that autumn is upon us.  These familiar black and reddish-brown caterpillars are larval Isabella moths.

The woolly bears that we see in the fall are the second generation of woolly bears for the year; the first generation hatched out in May.  This second generation of woolly bears emerged back in August.  Since then , they have eaten leaves from a variety of plants from grasses to clover to trees and sunflowers.  Once the cold weather hits, the woolly bear finds a sheltered spot like rotted log, or under a rock, or in a pile of leaves, to overwinter. When the temperatures drop below freezing, woolly bears also freeze.  Fortunately woolly bears have a cryoprotectant, a natural sugar-based antifreeze which protects the caterpillar’s tissues from being damaged when it freezes.  In spring, woolly bears emerge from their sheltered spot, eat a few more leaves then make their cocoons and undergo metamorphosis to become an Isabella moth.

Folklore has it that woolly bears predict the severity of the upcoming winter based on the proportion of black and reddish brown banding on the caterpillar’s body.  A thin reddish brown band means we are in for a tough winter.

But is this folklore true?  Dr. C. H. Curran, curator of insects at the American Museum of Natural History in New York City (1928-1960) traveled to Bear Mountain State Park in 1948 to find out.  On a single day, he gathered as many woolly bears as he could find, compared the reddish brown segment to the black segment, then reported his findings and a winter weather prediction to a reporter at the New York Herald Tribune.  Dr. Curran continued his study for eight more years and was never able to conclude whether the woolly bear was able to predict the winter.

More recently scientists have found that the size of the reddish-brown band increases as caterpillar matures and that wet weather increases the size of the black bands.

While woolly bears may not be an accurate forecaster of the upcoming winter, they are still a delight to see during a visit to a park.  Perhaps you’ll see one curled in a ball or looking for the next leaf to eat.

Post by Susan Carver, OPRHP.