Can Woolly Bear Caterpillars Really Predict Winter Weather?

We find out if there's science behind the claim.

December 21, 2016
woolly bear caterpillar on gravel
pavels/ Shutterstock

You may have seen this critter recently: the woolly bear caterpillar, aka the larva of a species of tiger moth. They’re bristly, with black stripes at each end and a reddish brown stripe in the middle—and pretty darn cute (almost as cute as these interspecies best friends). They’re also the subject of a strange bit of folklore.

In fall, woolly bears cross roads or paths searching for protected places to hibernate, traveling up to a mile a day—and if you catch a glimpse of one, some say you might be able to tell what Old Man Winter has in store. 


Related: 8 Gardening Tasks You Should Do This Winter

Supposedly, the longer the reddish brown band, the milder winter will be; while longer black bands mean bitter cold and lots of snow are on their way. But is this tale of old really true?

Turns out, those stripes do tell you something about the woolly bear’s environment, but probably not about future weather. According to the National Weather Service, the caterpillar’s coloring is based, in large part, on how long the caterpillar has been feeding. The better the growing season, the bigger the caterpillar will grow, which results in larger black bands and a narrower reddish brown band. Meaning, the coloration is more of a recap of the previous season, not an indicator of the one to come. 

Related: 6 Ways To Embrace Hygge, The Danish Secret To Staying Happy During Winter


Needless to say, you shouldn't put too much faith in this as a weather-predicting tool, but don’t discount it as a potentially fun family activity. (Another fun idea: decorating an edible holiday tree for your backyard birds.)

If woolly bears are already hibernating in your area, you’ll have a chance to spot them again in spring, when they resume eating until pupating in a cocoon and emerging as adult moths two weeks later. 

Oh, and don’t worry about them ruining your garden either—they are not one of the 15 worst garden pests. In fact, they can actually be an asset, as they eat mostly weeds, including dandelion, clover, and grasses, and generally will not harm your ornamentals or vegetables.