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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>Chuckyluck</span> Thu, 08/28/2014 - 17:13
Isabella caterpillars have bands of varying widths -- all in the same locality and same year. Go figure!! Black woolybears have black hairs covering the body. Fun to handle. Their hairs are really stiff. Saltmarsh caterpillars have MANY color phases. Yes, some are white, others yellowish, some even dark. Sometimes this species is considered to be a crop pest -- defoliator. Google this species, and enjoy its variability. Their hairs are long and soft.
<span>Rebecca A H</span> Mon, 08/18/2014 - 13:58
I see the brown and black ones all the time and i enjoy having them around. I always help them by pickin them up so no one runs them over when they cross the road. There such wonderful creatures its a shame when people kill them. I hope they are harmless cause ive touched them all my life and ive never been harmed.
<span>Lisa From Louisville</span> Thu, 08/14/2014 - 17:38
Just saw my first Wooly Worm of the season...we live near Louisville...he's ALL brown!!! What kind of winter are we in for?
<span>Thomas Hopper</span> Tue, 08/26/2014 - 20:13
during July of 2014, I have found 3 of these creatures. I have NEVER seen one in this area before September. Their bands looked normal, but I think we are in for an early winter, at least in Kansas.
<span>Taryn</span> Sat, 07/19/2014 - 11:00
wooly bears cannot predict winter. their coloring and thickness of hair may be because of different species, or even just because of different regions from which they are found.
<span>Jw King</span> Sat, 07/05/2014 - 13:10
July 5, 2014. I am very aware of the Wooly Worm. For years I have see all black, all brown or black & brown. While picking beans, I lifted a vine and on the main stalk was a WHITE Wooly Worm. What I saw, I saw. It was a Wooly Worm, only WHITE. I left it alone to feast on anything it likes.
<span>Leah Ct</span> Mon, 09/01/2014 - 21:51
I also found a white wooly worm this season. I have never seen one before!
<span>Jae</span> Mon, 09/08/2014 - 10:59
What is an all white wooly worm??? I am in central Illinois and just found a large amount resting on my shrubs. Never seen white ones before. Is there a way I could also attach a picture or do you know what it is without further identification needed.
<a title="View user profile." href="/author/editors">The Editors</a> Wed, 09/17/2014 - 15:03

There are several varieties of caterpillars that look like the woolly worm but are whitish. For example, the Virginian tiger moth caterpillar (Spilosoma virginica) is called the yellow woolly bear, which can range from white or pale yellow to reddish or brownish yellow.

http://www.butterfliesandmoths.org/species/Spilosoma-virginica

http://bugguide.net/node/view/498

Or, there is something called The Laugher, with a black head (Charadra deridens)

http://www.npwrc.usgs.gov/resource/insects/cateast/charderi.htm

http://www.discoverlife.org/mp/20q?guide=Caterpillars

The American dagger moth (Acronicta americana) also has a fuzzy white caterpillar, with black tufts and a black head.

http://bugguide.net/node/view/574806

The sycamore tussock moth (Halysidota harrisii) has orange and white tufts on cream to white fuzzy body, and an orange head.

http://bugguide.net/node/view/423

The Hickory tussock moth (Lophocampa caryae) has black tufts and a black area along its back:

http://bugguide.net/node/view/5690

https://www.maine.gov/dacf/mfs/forest_health/insects/hickory_tussock_moth.htm

Hope this helps! Happy sleuthing!

 <span>Ken Childs</span> Sat, 11/01/2014 - 12:30
You might want to add this information about other fuzzy caterpillars to the article since it's clear most people commenting haven't seen it. Also, there are all black fuzzy caterpillars such as Hypercompe scribonia which are out and about at the same time as Pyrrharctia isabella.