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Woolly Bear Caterpillars: Identification and Winter Weather Lore

a woolly bear or a woolly worm caterpillar, brown and black, on pavement.

Based on the measurements of the distinctive woolly bear caterpillar, you can figure out your weather forecast!

Image Credit:
University of Missouri
Written By: Jess Sullivan Digital Editor

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. 

Before making your own winter forecast, take a closer look! Not every fuzzy caterpillar is a woolly bear, and even woolly bears can vary in color. Here’s how to identify one and read its bands.

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 banded woolly bear is usually black on both ends and rusty brown in the middle, though some are mostly—or even entirely—black or rusty brown.

White or yellow fuzzy caterpillars are often different species, some also called “woolly bears,” rather than the familiar banded woolly bear of winter folklore.

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.

Banded woolly bear caterpillar with black ends and a rusty-brown middle beside an Isabella tiger moth
The woolly bear caterpillar (left) grows into an Isabella tiger moth (right).
Credit: SillyPuttyEnemies / Andy Reago & Chrissy McClarren

What Do Woolly Bear Colors Mean for Winter?

The woolly bear caterpillar has long been associated with winter weather. According to folklore, the woolly bear’s 13 body segments represent the 13 weeks of winter. Here’s how to read its colors:

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. 

winter weather folklore, using a woolly bear caterpillar to predict winter

Can Woolly Bears Really Predict Winter Weather?

That’s part of the fun of woolly bear folklore! Their colors aren’t a proven way to forecast winter, but one entomologist decided to put the legend to the test.

Between 1948 and 1956, Dr. C. H. Curran counted the rusty-brown segments on woolly bears. His counts suggested milder winters—and lo and behold, the winters that followed were milder than average! Still, Curran knew his samples were small. He was having fun with an old tradition, not claiming a scientific breakthrough.

Try Your Own Woolly Bear Winter Forecast!

Spotted a woolly bear? Take a look at its black and rusty-brown bands and make your own winter prediction! Do your fuzzy forecaster’s predictions match the Almanac’s winter outlook?

Watch a woolly bear in action in this short video!

Whether it’s fact or folklore, we always enjoy the fun! Share what your local woolly bears are predicting in the comments below.

Frequently Asked Questions

  • Is a woolly bear the same as a woolly worm?

    Yes! “Woolly bear” and “woolly worm” are both common names for the black and brown banded fuzzy caterpillar that becomes the Isabella tiger moth. You may also see them written as “wooly bear” or “wooly worm,” with one “l.” Despite the nickname, it’s a caterpillar, not a worm.

  • What do woolly bear caterpillars eat?
    Woolly bear caterpillars eat the leaves of low-growing plants—think dandelions, plantain, dock, asters, goldenrod, and even some grasses.
  • Are woolly bear caterpillars poisonous or safe to touch?
    No, woolly bear caterpillars aren’t poisonous or venomous. They don’t sting, but their bristly hairs can irritate sensitive skin. The safest bet is to enjoy watching them without picking them up.
  • Where do woolly bear caterpillars live?
    Woolly bear caterpillars live all over North America—from the United States and Canada down to Mexico. Look for them around grasses and weeds. When fall rolls around, you might spot them seeking shelter under bark, rocks, logs, or a cozy pile of leaves to ride out the winter.
  • What do woolly bear caterpillars turn into?
    Woolly bear caterpillars become Isabella tiger moths (Pyrrharctia isabella), with cream and yellow-orange wings spotted with black. After spending winter as caterpillars, they spin cocoons in spring and emerge as moths.
Weather Lore
Sources
  1. National Weather Service — Woolly Bear Caterpillar - Winter Predictor Or Not?
  2. Iowa Department of Natural Resources — Winter Is Coming: Can the Woolly Bear Predict It?

About The Author

Jess Sullivan

Jess Sullivan

Digital Editor

As Digital Editor of The Old Farmer’s Almanac, Jess is dedicated to bringing readers content that is accurate, clear, useful, and engaging. She has years of experience crafting written communications ...

Read more from Jess Sullivan

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Comments

<span>Crystal Fry</span> Wed, 10/09/2013 - 10:47
Saw a big fuzzy black one with very few brown on it here in Shippensburg,PA
<span>Robyn Douglas</span> Mon, 10/07/2013 - 20:12
I live in Lafayette Indiana and have seen only all cinnamon colored wooly bears so far this year. We can only hope they're telling the truth.
<span>Carolrae</span> Sun, 10/06/2013 - 18:43
I was so excited to find my first wooly bear of the year and it was a doozy. Very large solid black one - just gorgeous!-in Des Moines, IA.
<span>Elayne K</span> Thu, 10/10/2013 - 17:35
I live in Earlham Iowa & just found another totally black wooly a few minutes ago. It was headed South. Guess time to get the farm ready for another winter like last year.
<span>Jodie Sz</span> Wed, 10/09/2013 - 14:08
A large all black one may have been the Giant Leopard Moth caterpillar. I've been seeing lots of the Woolly Bears while walking my dogs in Mid-Michigan and the little guys have been mostly brown with little black. But today I say the big black one and brought it home to identify it, he is back outside now. Here's a link to a webpage about the leopard moth. http://bugguide.net/node/view/595354
<span>Dr. Jim Chapple</span> Sat, 10/05/2013 - 11:29
Check out Vermilion, OH as October 6 is the annual Woolybear Festival..the largest one day festival in the state of Ohio with the longest parade. Check out the city website!
<span>Rachel Hunter</span> Fri, 10/04/2013 - 13:07
I just found my first alive Woolly Bear that no one had squished - never will understand why people squish these cute little guys! I live in Ohio, usually the Woollys I find have little dark-brown, almost black butts, with brown-orangey mid sections. But the one I just found today is almost all the orangey-brown color! He has a teeny tiny black band by his head and that's it, goes back to orangey-brown! :)
<span>Marrbsst</span> Fri, 10/04/2013 - 11:25
I have been observing the critters for about a week now busily crossing the parking lot when I walk each day at work. I have seen at least a dozen of them each day. The days have been unseasonably warm here in Augusta, ME. Nice wide brown bands. Perhaps a mild winter? I wouldn't have called last winter mild, more like normal.
<span>Mallori</span> Thu, 10/03/2013 - 09:19
This is awesome. I'm from Ohio and I found a really fat fluffy black and brown one. It scared me at first I had all the lights out and I saw something crawling around the floor when I moved the stool and turned on the lights it took me a second to recognize it then I was like come on little fella your going outside. I wonder is that good luck to find one on your bedroom floor?
<span>Brady</span> Thu, 10/03/2013 - 09:15
Walking in Winooski, VT we have seen about 9 Woolly Bears, with normal reddish-brown stripes and black ends, about average length. Fuzzy and cute as usual.