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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>Kentuckywoman54</span> Mon, 10/19/2009 - 16:48
I was raised on this way of forecasting the winters. The woolys here in my part of Ky. are showing very little brown. Very large area of black on both ends. Will be interesting to note what kind of winter we end up with. Unusually cold for this time of year and early frost so far...
<span>Wolley Nut</span> Mon, 10/15/2012 - 17:51
I live in N.E. Ohio just east of Cleveland and the wolly bears I'm finding are almost all brown with only the very tips on each end black. This would indicate a warm winter here. I hope they are right.
<span>Chyk</span> Mon, 11/05/2012 - 15:49
I live in this area of Ohio too and the Woolies we've seen have a large brown middle with just the ends being black. Just like last year! My bet is on the Woolie and we are having a mild winter (so I hope!)
<span>Buck Hunter</span> Wed, 10/17/2012 - 10:45
I live in the same part of Ohio I've been out archery hunting for the past few weeks and seen dozens off woolly bears with little to no brown stripe and the buck I got Monday over I'm pa had more fat on real it then pony deer I've ever got I would say we are going to have one real bad winter
<span>Tigress</span> Mon, 10/19/2009 - 12:40
I have also heard this all my life and I agree has been accurate to a point. My belief is old sayings from generation to generation have thier reasons to carry on, If they did not believe in knowing what they see to be the truth, which is to predict the coming winter. Good feeling to read this article. Thank you
<span>Awtup6H</span> Sun, 10/18/2009 - 20:14
i have heard as a child for weather forcasting the catapiller is quite accurate in priducting the coming winter
<span>Craig King</span> Fri, 10/16/2009 - 19:50
This is something I've heard all my life, passed down from several generations in my family. I never made the empirical observation myself, but my grandmother did every year, and she swore by it! Some other signs she looked for were the thickness of hulls on hickory nuts and walnuts, and if the garden produced a bountiful crop that summer.
<span>Howard Kruse</span> Wed, 12/09/2009 - 09:36
I have to agree some with Craig King. I have watched the Wolly Worm for years but have not gotten any answers about the weather. I find the the Quantity of Nuts and wild berries that are produced, the thickness of the shells are a better clue as to the temperature of the winter. Also find that the closer to the ground that the wasps and hornets build their nests in the summer the colder it will be in the winter. I think that folks in different areas have their own special ways of determining how they think the weather is forecasted in that area. Hardyville,Va
<span>Edgar Toensing</span> Mon, 10/29/2012 - 19:20
In MN, we know we are in for a long winter when the highway crews are putting up snow fences in Aug.
<span>Krenaudsmith</span> Wed, 10/14/2009 - 18:58
hmmm very cool and my daughter was facinated when i read it to her