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

720x480-bvc-2020-post-roll.jpg

Reader Comments

Leave a Comment

Wooly worms

September ,2016 , every wooly worm I have seen in Ohio has been all white. Does this mean we're in for a snowy winter??

I have seen all white as well

I have seen all white as well and I live in SW Virginia. I sure hope it don't mean all snow!

I too JUST saw My First White Wooly Worm!!

My 14yo GrandDaughter had just drove in driveway and she spotted Many (6+) Wild Turkey and shortly iS
Iced the white wooly at base of a tree!:) Sophia said it must mean a very white winter!:)?? Am also anxious for Replies also as Tammy!:)) Come on y'all!! I know someone out there has some awesome Tales!:) Blessings to ALL!!! (And yes we live in KY .. Outside BeaverDam, Ohio County!:)

White Wooly Worm

Same here Sothern Ohio I have seen 2 so far, both as white as can be.

Winter 2916

So what's the prediction for this year

Wooly bear caterpillars

In Delaware I Have seen several wooly bear caterpillars, all of which have been totally blond this month. Hopefully we will have a mild winter!

Looking for data

I would love to use this for data analysis in my AP Biology class. Does anyone know where I can find data supporting or refuting this hypothesis about the weather/woolly bear relationship?

Black woolly bear caterpillar

Saw the first black woolly inside a massive vine growing on a railing on the deck on August 31, 2016. I live in Elizabeth City, N.C.

wooly bear

Just saw a black wooly bear in my garage a while ago. 08/28/2016. Plan to keep for the grandkids to see.

wooly worm - gray

first ones i saw today 8/25/16 saw 3 and all of them were gray or silver what does this mean, i live in middle of kansas

Just saw a completely black

Just saw a completely black one on the side of my house here in south western West Virginia. I seriously hope this doesn't mean we are in for a bad winter.

Black Wooly Bear!

I saw a completely black one today also, Cindy! I am in SW PA near Pittsburgh. I came to this page curious to find what it meant. According to this article, it would indicate a MILD winter--which seems to be completely opposite what other prognosticators are predicting!

It depends where you live.

The Editors's picture

It depends where you live. The Old Farmer’s Almanac (unlike many folks) is also predicting a fairly mild winter in some regions.  See our long-range weather maps and forecasts for winter 2016–2017 here: http://www.almanac.com/content/long-range-forecast-2017

read the first wooly you see

the first for 2016 was seen today and observed to be all orange (amber). My insights call for an extremely variable late fall, winter, early spring with some horrific turbulence. A very early snowfall is forecasted with abnormally strong and stormy weather extremes, both hot and cold, wet and dry.

wholly worms

Just saw a solid tan one in east Tennessee.

wooly worms

I saw an all orange wooly bear yesterday..8/27/16

Just found and all yellow one

Just found and all yellow one is western PA. First time I've seen one

Wooly bears

I remember playing with one with my grandpa when I was but a wee lad . When you first pick one up it goes into a circle and you can scootch it around in your palm - it tickles! then it uncurls and roams around heading for the highest point on your hand. I never hurt one, just played with it for a bit then put it back where I found it. Wooly Bears Are Neat Critters!!

A solid black woolly worm wow

A solid black woolly worm wow our nation is out of control...

Black wooly bear

I found a solid black one a couple of days ago in Middle Tennessee.

I wasn't familiar with them, so put it in a container with plenty of clover and other greens, and when I checked today, it has built a web and the pupae is inside. Guess I'll be seeing it transform before long.

I found a solid black one too!

Here in Louisville, Kentucky; I found a solid black wooly worm, never seen one all black before either. Sadly it was dead.

Black Wooly Bear

I just saw a solid black wooly bear on my patio in DFW Texas. First I've seen; he is very active, travels fast!

Wooly Bear in danger

We found a Wooly Bear under a frozen glove on the side of our house. We brung it inside and warmed it up. It is up and moving now, and we plan to keep it until after the winter storm. We are most likely going to walmart to get some Violets for it to eat .. is that the right thing to do?

Oh, bless! It’s too bad the

The Editors's picture

Oh, bless! It’s too bad the wooly worm picked the frozen glove. During the winter months, wooly bear caterpillars do not need to eat. Instead, they hibernate, or sleep, in a safe spot all winter long. When spring returns, wooly bear caterpillars wake up. You might want to put him in a safe spot! It’s hard to say if he’ll survive, but it’s very kind of you to try.

Once they wake up in the spring, they enjoy clover But they’ll known to eat herbs, grass, dandelions, and sunflowers.

Southern Illinois

All black here.

Can't see info stated in title

Perhaps my phone isn't displaying pages correctly because all I can see is the information leading up to and including the facts and lore. I can't see any information that tells you how the colors predict the weather or what the colors mean. Maybe it's just my phone though.

Ohio- found an all black

Ohio- found an all black woolly bear! what does this mean! winter is approaching

Albino Wooly Worm

Any predictions for our winter based on an "albino" wooly worm?

animals

In the book of Job in the bible there is a verse were he says animals can teach us things Job 12 : 7 Niv bible .

woolly worm

I just saw an all-black woolly worm this evening. It was the first one I had ever seen. It was about 2-1/2 inches to 3 inches long and 1/2 inch to 1 inch wide. It was interesting to see but it gave me the creeps. I don't know where it went-- somewhere in the yard, I hope. I saw it go down the side of the porch but it backed up and was on the top of the porch again. However, I missed seeing it disappear!

Pages