Woolly Bear Caterpillars and Weather Prediction

Using Woolly Worms for a Winter Forecast

August 30, 2018

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

University of Missouri

The woolly bear caterpillar—also called woolly worm and fuzzy worm—has the reputation of being able to forecast the coming winter weather. Whether this is fact or folklore, learn more about this legendary caterpillar and how to “read” the worm.

Here’s the legend: The Woolly Bear caterpillar has 13 distinct segments of either rusty brown or black. 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. 

How the Woolly Bear Caterpillar Became “Famous”

  • In the fall of 1948, Dr. C. H. Curran, curator of insects at the American Museum of Natural History in New York City, took his wife 40 miles north of the city to Bear Mountain State Park to look at woolly bear caterpillars.
  • Dr. Curran collected as many caterpillars as he could in a day, determined the average number of reddish-brown segments, and forecast the coming winter weather through a reporter friend at The New York Herald Tribune.
  • Dr. Curran’s experiment, which he continued over the next eight years, attempted to prove scientifically a weather rule of thumb that was as old as the hills around Bear Mountain. The resulting publicity made the woolly worm the most recognizable caterpillar in North America.

Woolly Bear Caterpillar. Photo by SillyPuttyEnemies/Wikimedia Commons.
Woolly Bear Caterpillar. Photo by SillyPuttyEnemies/Wikimedia Commons.

What is the Woolly Bear Caterpillar?

The caterpillar Curran studied, the banded woolly bear, is the larval form of Pyrrharctia isabella, the Isabella tiger moth.

  • This medium-size moth, with yellowish-orange and cream-colored wings spotted with black, is common from northern Mexico throughout the United States and across the southern third of Canada.
  • As moths go, the Isabella isn’t much to look at compared with other species, but its immature larva, called the black-ended bear or the woolly bear (and, throughout the South, woolly worm) is one of the few caterpillars most people can identify.
  • Woolly bears do not actually feel much like wool—they are covered with short, stiff bristles of hair.
  • In field guides, they’re found among the “bristled” species, which include the all-yellow salt marsh caterpillar and several species in the tiger moth family. Not all are ‘woolly bears!’
  • Woolly bears, like other caterpillars, hatch during warm weather from eggs laid by a female moth.
  • Mature woolly bears search for overwintering sites under bark or inside cavities of rocks or logs. (That’s why you see so many of them crossing roads and sidewalks in the fall.)
  • When spring arrives, woolly bears spin fuzzy cocoons and transform inside them into full-grown moths.
  • Typically, the bands at the ends of the caterpillar are black, and the one in the middle is brown or orange, giving the woolly bear its distinctive striped appearance.

Isabella Tiger Moth. Photo by Andy Reago & Chrissy McClarren/Wikimedia Commons.
Isabella Tiger Moth. Photo by Andy Reago & Chrissy McClarren/Wikimedia Commons.

Do Woolly Bear Caterpillars Forecast Winter Weather?

Between 1948 and 1956, Dr. Curran’s average brown-segment counts ranged from 5.3 to 5.6 out of the 13-segment total, meaning that the brown band took up more than a good third of the woolly bear’s body. The corresponding winters were milder than average, and Dr. Curran concluded that the folklore has some merit and might be true.

But Curran was under no scientific illusion: He knew that his data samples were small. Although the experiments legitimized folklore to some, they were simply an excuse for having fun. Curran, his wife, and their group of friends escaped the city to see the foliage each fall, calling themselves The Original Society of the Friends of the Woolly Bear.

Thirty years after the last meeting of Curran’s society, the woolly bear brown-segment counts and winter forecasts were resurrected by the nature museum at Bear Mountain State Park. The annual counts have continued, more or less tongue in cheek, since then.

For the past 10 years, Banner Elk, North Carolina, has held an annual “Woolly Worm Festival” each October, highlighted by a caterpillar race. Retired mayor Charles Von Canon inspects the champion woolly bear and announces his winter forecast. 

If the rusty band is wide, then it will be a mild winter. The more black there is, the more severe the winter. 

Woolly bear caterpillar in defensive posture.
Woolly bear caterpillar in its defensive posture.

Most scientists discount the folklore of woolly bear predictions as just that, folklore. Says Ferguson from his office in Washington, “I’ve never taken the notion very seriously. You’d have to look at an awful lot of caterpillars in one place over a great many years in order to say there’s something to it.”

Mike Peters, an entomologist at the University of Massachusetts, doesn’t disagree, but he says there could, in fact, be a link between winter severity and the brown band of a woolly bear caterpillar. “There’s evidence,” he says, “that the number of brown hairs has to do with the age of the caterpillar—in other words, how late it got going in the spring. The [band] does say something about a heavy winter or an early spring. The only thing is … it’s telling you about the previous year.”

Every year, the wooly worms do indeed look different—and it depends on their region. So, if you come across a local woolly worm, observe the colors of the bands and what they foretell about your winter weather.

What’s the real winter weather prediction for 2018The 2019 Old Farmer’s Almanac was just released! Look inside for our official forecast!



The 1998 Old Farmer's Almanac


Reader Comments

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seen first woolly bear worm today

3/12/17 find it odd to have my first woolly bear today. I live in northern wisconsin and he was in the lawn frozen. I felt sorry for him so I brought him in the house to see if he would thaw out, He did :). Within an hour he was moving around. I put some grass in the bucket for him, I hope he makes it till it warms up so I can put him back outside. Any suggestions on these?

Not sure how "frozen" it

Not sure how "frozen" it really was. Interesting fact, in northern latitudes, woolly bear accumulate glycerol to enhance their diapause freeze tolerance.

Wooly Bears

Saw a wooly bear crossing my lawn yesterday here in Oregon, equal stripes of black and orange. It seemed odd to see him this time of year. We have had an unusually cold, icy and snowy winter so far for the Multnomah Valley. Right now it is milder (a bit over 40 degrees) and raining - maybe that's what made him come out.

All brown in Ulster County/Accord, NY!

On my New Year's Day run I saw a wooly bear crossing the road that was all brown. There was no black to be seen. I thought it was strange but then, it's 60 degrees here in NYC today and all next week the temps are predicted to be in the 40s and 50s. Hmmm .....

Solid black

Saw a solid black wooly bear in Pennsylvania

Woolly Bear Caterpillar

I just found this caterpillar crawling very slowly in my basement. He has equal segments of brown and black. My house is about 150 years old on a farm in Ontario, Canada. I don't know what to do with him, any ideas?


I just found one in my basement tonight. I'm wondering where he came from! I don't know what to do with him. Lol

Brown with black stripes

In central Indiana in October and November I saw a lot of black ones crossing the road, but when I took a closer look they were orangish brown with black stripes at each end. I was told this meant a cold snap at the beginning of the winter (which we are having now) followed by a mild or normal winter with a cold snap at the end. I hope wooly worms are better meteorologists than groundhogs.

First weekend of November, I

First weekend of November, I saw a total black woolly warm. My immediate thought, was...oh no! A severe Winter. I guess time will tell. Most forecasters are calling for a mile winter in Northeast North Carolina. I have never seen a black one before. My first. I was explaining about the woolly warm to several friends and they thought I was making this stuff up. So this is a great piece I will share with them. I guess we will stay tune and see what ole Jack Frost and Mr. Winter has in store with us.

Here in Maryland they are

Here in Maryland they are black.

I have encountered numerous

I have encountered numerous totally black Wooly Bears this past Fall on my county road trips surrounded by bean and corn fields here in South Central Indiana. It will be interesting to see if it does affect our winter. Here it is the first week of November and it has been unseasonably warm up to this date. I guess look out for February and March this upcoming year.

I spotted several wooly bears

I spotted several wooly bears while driving thru Kentucky last month. I noted they seemed totally black from where I sat in the passenger seat. Severe winter, we shall see.

Yes I've seen at least 8

Yes I've seen at least 8 wooly worms and they where all black ,so I guess we might have a severe winter just have to wait and see

We were hiking the Walkill

We were hiking the Walkill River preserve, saw over 25 wooly bears, all with larger brown segments than black, also spotted an all light tan one, they were very active due to the warm day. Looking forward to the mild winter.

I have seen several crossing

I have seen several crossing the road as I have been driving here in Blue Rock Ohio. Today I pulled over to take a Picture of the very large (biggest one that I have ever seen) All Black Woolly Bear. I have yet to see one with any brown . I have a few Local friends who have reported seeing all white Woolly Bears too.

Woolly caterpilliars in nw pa (lake erie)

Saw a woolly caterpillar (Mon-10-24-16). Black head with large middle of the brownish orange and the end black. Some say it will be a mild winter, while others say if it has a black head, winter will be bad. What is the myth? Hoping for a mild winter.

Wooly Worms

There's also a festival in Beattyville, KY. Although probably not as large as the one in NC. Seen a lot of all black worms this year- and we did have a cold, snowy winter last year.

Woolly Bear

While walking trails along the Blackstone River we saw a tiny Woolly Bear mostly Black but only about 1 inch long . So Cute Can you bring in House to watch it???? We live in Mass along the River.

wooly worms????

What does the all tan one mean. i just seen one on the porch.


the tan or sometimes all white wooly worm is said to report a very snowy winter.

Wooly in Wisconsin

In SE Wisconsin I have been seeing Woolys that are mostly black with a small band of brown. I have seen a few that look solid black also.

Mild winter

Looks to be a mild winter here on the Texas Gulf Coast. Wooly worm had equal bands of black and brown.

Newell wv

I've seen more black woolly worms then the brown

Black Woolly Warms in WV

I live in Huntington, WV. I've seen only two woolly warms on my back porch and both were completely black...could it be the same one twice over a couple of weeks time...sure but don't think so. From my understanding, this means a colder, snowier winter.
I spoke with a customer the other day at work and she saw a completely white woolly warm...I asked her what that means seeing how I've never heard of that and she said research it. I did and I discovered it "means" blizzard like conditions!
I say to you all, I hope so!!!!

Happy Winter to ya'll as we say in WV!

mild winter michigan

just saw 3 woolly's in the garden all three mostly brown. but yet forcast for us in COLD and Lots of snow guess we'll see you is going to be right

All black woolly spotted

Lansdale, PA, very large, all black woolly spotted in my garden yesterday...so what are we in for winter weather-wise?

Black Woolies

I live in Northwestern PA and have only seen all black Woolies so far. I guess we can't complain, as last winter was wonderful, not much snow!

White/Creamish Wooly Worm

I just saw a THICK white one on my back door two days ago. I'm in southern NC so, I'm used to black, brown, and black/brown but, never white! We don't really get much actual snow (we get ice) in my part of the state so, I guess I'd better hold on to my hat!

All White Caterpillar 2016

I just seen an all white one this month, and it showed a brown streak on it's back , which indicated a mild winter with a streak of harsh winter, which is exactly what we had in 2015 / 2016 winter. Hopefully that will be the same for 2016 / 2017 winter.

wooly bear

today, september 27th 2016, i spotted a totally black wooly bear......... cold winter????