Woolly Bear Caterpillars and Weather Prediction

Do Woolly Worms Really Predict Winter Weather?

August 28, 2019
woolly-bear-caterpillar-winter

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 or 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 one of the most recognizable caterpillars in North America (alongside the monarch caterpillar and tomato hornworm).

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

What is a 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, particularly in 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 woolly caterpillars are true ‘woolly bears’ though!
    • If you find an all-black woolly caterpillar, don’t worry—this doesn’t mean that we’re in for a severe, endless winter! It’s just a caterpillar of a different species, and is not used for forecasting. The same is true for all-white woolly caterpillars. 
  • 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 prediction for this winter? Read our official winter forecast here: 

Source: 

The 1998 Old Farmer's Almanac

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Reader Comments

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Woolly bear

Just saw our first woolly bear. We found it in our hydrangeas. It is about equal parts brown and black. So cute! I live in NE Ohio, not far from the home of the Woolly Bear Festival.

Woolly bear sightings in Maine

4 woolly bears sighted in various locations in foothills of western Maine, all rusty colored, no black.

Woolly Bear caterpillars

I haven't any Woolly Bears so far this year but it's been super hot here in Texas so I guess we'll see them when it gets cooler. They are always crawling into the patio area where my cats sleep and I have to put them back into the yard. I had never heard of or seen these before moving here from Virginia but I think they are beautiful. I was used to the green caterpillars when growing up and it always excites me when I see a Woolly because they make me think of Halloween which is my favorite holiday.

Caterpillars

Noticed very black caterpillars crossing roads in MD.since July 4th weekend.few years back when I saw them it was cold and wet winter...id bet we freeze this winter..its yet to be seen...but nature is quite funny how it acts.

Wooly bear caterpillar nickname

We've been calling them B. O. B. {Black orange black} since we were kids. Don't know if it's just us or do others also share this fun nickname?

Wooly Bear Catapillar

The wooly bear is black on each end & a beautiful dark mahogany brown in the middle. I have lived near Concord NH since 1960. It is the late Fall/Autumn wooly bears we look for while putting the yard to bed for winter. Only the late fall woolies accurately predict the winter season. The wooly bear mostly predict the severity of the cold along with the snowfall or the upcoming winter & Spring. The brown is the weather part. If the brown is short the severity of winter is short, if long the severe weather is long. Also, & most important... if the brown is toward the head the winter weather will come early, if toward the tail spring weather will be late; & vice versa. We have been following this for planting/growing seasons since 1960. So if the brown is close to the head & close to the tail = early winter & late spring. If brown is short & in the middle of the caterpillar = late winter & early spring. Since 1960 I have written down what late fall woolies looked like, & in my town & they have been correct 100% of the time. You must only look at your yard woolies Here in NH just 2 town over the winter can be totally differently on cold & snow fall. There is a caterpillar here that is black with just a pinstripe of brown, different species. The wooly bear is safe for kids to handle & great for kids to get an up close & personal interaction with nature. Setting them loose is personal, but some farmers & some garden websites say they are harmful to certain crops. The ones you see in the spring are last years woolys that have come out of hibernation & are looking for a place to turn into a moth, the moth lays eggs, the eggs hatch out the caterpillar; so you can only use the autumn wooly to predict the upcoming winter.

Woolly bear

So I just saw one ..May 14th 2019 ..here in my backyard in Coquille Or... we have a lot of them here..and it's middle was very long and very Reddish.. we had a very mild Winter here this past year... didn't even go through all my pellets or wood.. so MAYBE??? it is a past prediction...

It WAS a cold winter!

Just finished reading the article and the comments from late autumn 2018. So all those black wooly worms were right...it was really icy, icy cold. In Michigan school districts had up to three weeks of snow and cold day cancellations! This year we are doing a weather-related agriculture maze, so I am curious what other weather folklore is fairly accurate?

Wooly Bear Capterpillar

I found an all black, 2 to 3 inch long wooly bear on my patio this a.m. It was raining and not too cold outside. Now I am wondering if the rest of the winter will be really snowy and cold.

Woolley Bear Catapillar

Just found an ALL orange woolley bear in my christmas tree xmas 2018! Short winter?? Early spring??

orange caterpillar

The Editors's picture

Hi there! If it is truly a woolly bear caterpillar species, then folklore would say that it is predicting a very mild winter. The amount of orange on a woolly bear can actually be influenced by age, etc. An older caterpillar may have more orange. There are also orange, fuzzy caterpillars of other species–including the very odd-looking, and venomous, southern flannel caterpillar (aka puss or asp caterpillar), that lives from New Jersey on down to the southern states.

Wooly bear

Just saw a all orange wooly bear 12/31/18 on Nantucket, MA Short Winter?

very dark wooly

Location: Saint Louis I just found a woolly by the revolving door in our lobby. I thought it was all black but upon closer inspection it does have a short very dark reddish brown band. It's 22 degrees outside today but it's been in the 50's for the better part of the week. I made him a shelter in a small box with tissue but not sure what to do for him. Help!

Woolley Bears in barn

So far there are two just roaming around the barn. I move them under the hay but they just crawl back out and don't seem to have any interest in settling down yet. Almost completely orange so praying for a mild winter here in the Chicago-land area.

Woolly Bear caterpillars

We found three woolly bears in an log pile and they looked just like the ones in the picture. So it should be a normal winter in the suburbs of Chicago, IL. I found another place for them in an unused section of the log pile and I hope they will be okay for next year.

Wooly Bear Caterpillar

I rescued on from the lawn mower this afternoon. I gathered up some grass clippings and dry leaves and gave it a plastic box with holes in it and gave it a warm place to live untill the weather up here in Mass subsides on Saturday. Another Nor' Easter is nipping our heels for later today and into tomorrow. Then this weekend we will set Nostradamus free to become a pretty moth in the spring!!

Wooly Bear

I live in central Ohio and my Wooly Bears are mostly reddish brown with black ends. I wish I could post a picture. I took one yesterday.

Wolly bear caterpillar

My cats found a wolly bear caterpillar were in Absecon NJ it was more black

Wooly Bears Scientific Analysis 2018 - 2019

Perhaps someone at our wonderful Almanac publication could gather all the Wooly Bear sightings as reported here. As it seems there have been a varied crossection of N. America responded. Many of which are calling for harsh winters. I have not observed any yet, but plan to make a foray around our home in hopes if finding some and will report my sightings later.

There are not many items I find in my inbox that I enjoy reading more than my old Farmer's Almanac...thank you Ben and our current staff !

interesting

That’s an interesting idea. We have phenology charts for other types of spring sightings (first bud, etc.) and we have a foliage map.  Maybe a woolly bear map is worth considering! 

Wooly Bear All Black!

I saw on in October in upstate New York that was all black!!! We are in for it!

All Black!

Found one of these Woolly bear caterpillar's today while raking leaves and it was All Black. No brown segment at all this year. Uh Oh....lol

All Black!

Found one of these Woolly bear caterpillar's today while raking leaves and it was All Black. No brown segment at all this year. Uh Oh....lol

WOOLY WORMS

I live in southern Arkansas, northern Louisiana border, I have been seeing a lot of wooly worms, all black and about 3 to 4 inches in length... this legend has been passed down through the family, (yess,we have Native American Indian blood lines), and the story goes, the blacker the worm the colder the winter and the length of the worm, is the amount of snow that you will receive.... it hasn't failed us yet, so maybe the south is getting a good winter this year, we really need to get one, get rid of the mosquitoes..

Wooly worms?

Last year, I saw two of them on the side of my house...I live in Bixby, OK. I had never ever seen these before. Someone said don't touch them, they're fuzzy, spiky stuff can sting you?? Ok no big deal, it was only two.
This year?? We have had thousands!!!!! Alllll over my van, I'd think they're gone, be drivin down the street, open my window and almost immediately there would be one (or more than one!) trying to get in the window! They freak me out, I don't like them, at all!
My kids dont mind them, and also they haven't had hundreds on their cars like I have! I'm still seeing a bunch everyday, usually on my deck where I like to sit outside....I moved where I was parking my van, so they haven't really been on it recently....as I took the dog out today, one dropped outta the tree I was underneath, and landed right next to my foot! Freaked me out! I swear they have radar for me, the only one here afraid of them!
I don't understand how/why we only had a couple last year and this year soooooo many!! Does that mean we will have a ton again next year??? Ick! I want them to stop but they just keep coming and coming and coming!

Yellow in color

Forgot to mention that all of ours here are yellowish. Some white white ones, but mostly yellow. I've only seen one brown/black one and it wasn't at my house, it was somewhere else.

Wrong Caterpillar

Lisa, you are confusing two very distinct caterpillars. There is one yellow/white one that falls from trees and can sting you, but the caterpillars featured in this article is NOT that one.

Don't be afraid of them!

I pick them up whenever I think there's a chance that they might get stepped on. They are so cute. Not sure if they really do predict how cold winter will be, but it's fun to speculate! I've often thought of getting a bumper sticker that says, "I Brake for Woolyworms!" (a.k.a. Wooly Bear Caterpillars).

woolly worm

a customer of mine saw a prey mantis eating a woolly worm

Wolly worm

Found one thus morning more black then yellow bad storms According to this

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