Woolly Bear Caterpillars: Identification and Winter Weather Lore

Woolly bear caterpillars—also called woolly worms—have long been said to predict winter weather. According to folklore, the wider the rusty brown band on the woolly bear’s body, the milder the winter. More black? A harsher season may be ahead. 

All-black, all-white, or yellow fuzzy caterpillars aren’t part of the folklore. So, if you spot one of those, it isn’t forecasting an apocalyptic winter! Learn more about the legendary woolly bear caterpillar and how to “read” its colors to make your own winter weather predictions.

How to Identify a Woolly Bear Caterpillar

If you see a black and brown fuzzy caterpillar, there’s a good chance it’s a woolly bear! The woolly bear is often black on both ends and rusty brown in the middle, though some are mostly black or mostly rusty brown. 

The woolly bear caterpillar is the larva of the Isabella tiger moth (Pyrrharctia isabella), which has yellow-orange and cream wings spotted with black. Alas, the moths are not known for their weather-predicting abilities. 

Woolly Bear Folklore: What the Colors Mean

The woolly bear caterpillar has long been associated with winter weather. It’s said that the 13 segments on the woolly bear’s body represent the 13 weeks of winter. According to folklore: 

The wider the rusty brown sections (or the more brown segments there are), the milder the coming winter will be. The more black there is, the more severe the winter. 

Love weather lore? Read about more signs of a hard winter. 

Can Woolly Bears Really Predict Winter Weather?

Most scientists will tell you that the folklore of woolly bear predictions is just that—folklore. One Canadian entomologist did, however, put the legend to the test. 

Between 1948 and 1956, Dr. C. H. Curran set out to forecast the coming winter weather using woolly bears. His average brown-segment counts ranged from 5.3 to 5.6 of the 13 total segments on the caterpillar, meaning that the brown bands took up more than a third of the woolly bears’ bodies. 

Lo and behold, the corresponding winters were milder than average! 

But Curran was under no scientific illusion: He knew his data samples were small. Although the experiments made the folklore seem more believable to some, Curran was mainly just having fun. 

Try Your Own Woolly Bear Winter Forecast! 

If you come across a local woolly bear, observe the colors of the bands and what they foretell about your winter weather. Woolly bears’ markings vary from year to year and from region to region. Remember:

If the rusty band is wide, it will be a mild winter. The more black there is, the more severe the winter.

What do you think they’re predicting for the winter? Do their fuzzy forecasts match the Almanac’s winter outlook? We’ll leave the weather-prognosticating “skills” to your observation!

Did you know? The 2027 Old Farmer’s Almanac is now available! Get yours where books and magazines are sold, or order straight from Amazon to your home.

Whether the predictive powers of the woolly bear caterpillar are fact or folklore, we always enjoy the fun! Feel free to share your experience with the woolly bear in the comments below.