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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>Susan@Lambsbest.com</span> Sun, 10/10/2010 - 11:28
Georgia wolly worms/bears are all orange this year as well.
<span>Fireonered</span> Tue, 09/28/2010 - 10:03
NJ wooly bears are all orange this year too! I thought I was imagining it, but then I found this article. I wonder what is going on?
<span>Teddy</span> Mon, 09/27/2010 - 10:45
Wooly bears, Acorns and ice in the Northeast. This year there are so many acorns I cant walk a step in the back yard without stepping on three. The wooly bears are all orange though. This combination usually means that when we have precipitation we will see little snow, a lot of ice and the winter will be longer than normal. We are collecting the acorns for the deer due to the ice build up on trees will make it nearly impossible for them to get a decent meal in late february. Signing off in the lower hills of the Berkshires
<span>Nawe417</span> Tue, 09/21/2010 - 13:55
Here in S.W. Missouri, as far back as when I first came here in 1965, all the old folks predicted the winter as to how black looking they were. When lighter, a mild winter, when dark, a harder winter.
<span>Jbauer81</span> Thu, 09/09/2010 - 14:41
Our wooly worms/bears are all orange also! Here in central southern michigan. What does it mean?!
<span>Jjstewart</span> Mon, 08/30/2010 - 16:15
Our woollies have always had thick dark bands on them. yesterday I saw two without a single band....they were both a dark orange, very furry and quite large. what does this mean for this winter in southern Wisconsin?
<span>Glorioussnookie</span> Sat, 02/27/2010 - 07:36
I grew up in PA. One year I showed my Mom one I found, she said"Oh No are they all like that?" I told her yes, she said, we're in for a bad winter" Well those wooly bears were right, it was a terrible winter. this past fall in West TN the wooly bears were black and so far we have had 17 inches of snow when a normal total snowfall for the season may be 1 to 2 inches. I have lived here for 14 years and this is the first time I ever saw the wooly bears all black and I would definitely say they were right! So much for science ha!ha! GOD BLESS!
<span>Ron Ro</span> Fri, 11/13/2009 - 12:28
Interesting article -- but what does it mean when up here in central New York, neither I nor my family have yet to SEE even one woolly bear this Fall? It's the first time I can recall that happening in my 73 years up here.
<span>Kimmie76</span> Sat, 10/06/2012 - 21:40
As of October, 2012, I've seen 2 wooly bear caterpillers with NO BLACK. Does anyone know what that means for Catskill Mountain weather this season? Thanks!
<span>Theresa Upstate</span> Tue, 09/18/2012 - 11:43
In up state NY (Watertown) yesterday I saw my first Woolly Bear of the season and it was very black on both ends with an equal amount of rust in the middle. So in three parts two were very black and one deep rust. :)