Woolly Bears in a Winter Wonderland?


This time of year often invites a clash of clothing. It can be chilly in the morning, but by mid-afternoon we’re all running the air conditioners and peeling off layers. It can be tough to predict what the weather will be just a few hours from breakfast, never mind what it will be three months from now. But we try!



photo by Catherine Boeckmann

Whether you’re a diehard fan of the Farmer’s Almanac or an astute observer of woolly bear caterpillars, chances are good you play the prediction game. It’s human nature to want to know what’s coming up, so we can prepare by buying a new pair of heavy-duty boots or by booking our February vacations to Florida.

But how accurate can we really be? The tale goes that by observing the brown bands on woolly bear caterpillars, also known as the larva state of the Tiger moth, we can know whether it’s going to be a brutal winter or a mild one. If the bands are thin, stack the firewood high. If the bands are thick, don’t worry, it’s going to be an easy season.

Dr. Howard Curran, former curator of insects at the American Museum of Natural History in New York City, studied this phenomenon back in the 1950s. For several years, he and his wife spent their autumns gathering as many woolly bears as they could and measuring the brown bands. They didn’t claim to be doing a scientific study; they would’ve needed to track a much larger population over a greater amount of time to get results that could be considered conclusive. Instead, they were simply interested in casually observing the woolly bear population.

They found that about 80 percent of the time, the woolly bears accurately predicted the severity of the winter.

Before we put meteorologists out of business, consider the fact that most entomologists consider the woolly bear method of weather prediction to be a fun bit of folklore.

It’s been hypothesized that the bands on woolly bears might have more to say about the previous winter than the future winter. The earlier in the spring the caterpillars emerge from their eggs, the more time they have to grow wider bands before heading into hibernation in the fall. During milder years, eggs get laid earlier, and caterpillars have a longer period of growth before turning into moths.

The Farmer’s Almanac, which bases its predictions on historical data, says this winter will be a tough one across most of the country. National Oceanic and Atmospheric Administration (NOAA), which uses state-of-the-art instruments to track and model weather patterns, says not so fast. Woolly bears seem to be sporting average bands this year. The only way we can know for sure what the winter will be like this year? Wait a few months.