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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>Bbandgsmom</span> Mon, 09/16/2013 - 09:31
Last year (2012) we saw only a couple total for the whole fall here in Midwest Ohio; we had an extremely mild winter. This year, however, there is no shortage of our furry friends and in many colors. Makes me wonder whats in store for the upcoming winter!! Brrrrr
<span>Becca C</span> Fri, 09/13/2013 - 17:31
Found what seemed to be a white woolly bear in Lancaster, PA today. Never saw one that wasn't orange and/or black before. Cool to see others are as confused as I am as to what that might mean?
<span>Jodi Correll</span> Wed, 09/25/2013 - 20:22
I just saw a snow white one today. My first all white one and I'm 52!
<span>Judy Blank</span> Thu, 09/19/2013 - 16:10
I just saw a wooly bear on my front porch and it mostly reddish brown with a black head does it mean a hard winter?
<a title="View user profile." href="/author/editors">The Editors</a> Sun, 09/15/2013 - 12:15
As we understand it, there are many white caterpillars in the tiger moth family (many of which are called woolly worms or woolly bears). For example, a yellow woolly worm (Spilosoma virginica), also called the Virginia tiger moth, can appear in a white caterpillar phase. For photos of the various colors that this caterpillar can be, see: http://bugguide.net/node/view/498 Although folklore focuses on the banded woolly bear, which does not have a white phase, there are weather sayings related to pale or white woolly bears as well. Some say that pale woolly bears mean that a mild winter is expected, but white woolly bears mean that lots of snow is coming.
<span>Spring Skews</span> Sat, 09/14/2013 - 14:57
A few weeks ago my friend posted a pic of a pure white one on her desk. I dont know what it means either
<span>Diane Paquette</span> Sun, 09/15/2013 - 16:19
my husband and i were out moving the picnic table to mow the lawn and all of a sudden we saw wollybears every where not just by the picnic table but all out back we picked up 52 of them and they had small black tips and all brown in the middle neva saw so many ever!!!! saved em all i hope!!!!!!!
<span>Cathy L. Carter</span> Mon, 09/09/2013 - 20:42
Found the first wooly bear of the year here in Winston Salem, NC. It was small. It was black on the ends, brown in the middle.
<span>Ruru</span> Tue, 09/10/2013 - 21:19
I live in Daleville, VA and this week every wooly caterpillar I have seen has been completely black.
<span>Lucy Carpenter…</span> Tue, 09/10/2013 - 07:40
I am curious about the extent of the caterpillar determining the weather....Have been seeing a lot of white ones here in Brown County, Ohio, which is a first for me...Does anyone have any info about the white ones????