Woolly Bear Caterpillars and Weather Prediction

Using Woolly Worms for a Winter Forecast

August 30, 2018
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 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!

 

Source: 

The 1998 Old Farmer's Almanac

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Reader Comments

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White Ones are not Woolly Bears!

I keep seeing people post about white "woolly bears". There is no such thing. There are a couple of different species of moth caterpillars that are white and fluffy or fuzzy, but they are not true Woolly Bears(Isabella Tiger Moth). If you check online photos, you can see what the white fuzzy caterpillars are. I see the lovely fuzzy white ones around this time of year as well. They have much longer hair, are smaller and thinner.

White Wooly Bears

I live in Central Virginia. Every fall, thousands of wooly bears cross a certain stretch of my road. One fall day, I saw a sea of only white ones! I had never seen white ones before, and I haven't seen them since. That winter was nationally known as "Snow-Mageddon!"

Just saw a Woolly in East PA

It was a pretty even black, then brown, then black. We also saw an all black fuzzy caterpillar but we think it was a giant leopard moth caterpillar. So I guess we'll have an average winter? Too bad, I was hoping for a mild one lol.

predicting winter weather with wooly worms

you mention the brown and black band,but we've seen all white wooly bears,what does that mean?we live in upstate ny.

Enjoy the fuzzy wuzzies!  To

The Editors's picture

Enjoy the fuzzy wuzzies!  To our knowledge, there is no white form of the banded woollybear (woolly worm), which is the orange and black caterpillar that folklore normally associates with winter weather predictions. However, there are several caterpillar species that can be fuzzy and white or cream, sometimes with spots or tufts of a different color. As one example, the caterpillar of the Virginia Tiger Moth (Spilosoma virginica), called the Yellow Woollybear, can appear all white or all pale yellow or cream. It is in the same family as the banded woollybear, but a different genus. It can be found throughout most of North America.

Wooly worm

10/18/16 Saw a all black and a mostly orange band today. What does this mean? Same trail,same day and time!

My first white Woolley worm!!

I use these fun creatures every year and have never seen an all white before today. I live in Southern Indiana near Bloomfield. Bring on the snow!!

No Orange all Black Woolly Worm

I live outside Albany, NY and have seen a woolly worm that was totally black, no orange. Not that I'm hoping for a ton of snow, but in our area we're in a rainfall deficit.

WHITE Woolly Worms in West-Central INDIANA

Our family has ALWAYS predicted the upcoming winter forecast by the woolly worm and also by cutting the seed of a persimmon in half. This is the first year we have ever saw a white woolly worm! Our daughters are now 20 & 23 and STILL love this family tradition. It's too early for our persimmon forecast. Anxious to see what that prediction looks like!

White woolly catapillar

Watch out for the white one they are poisonous
I had one crawl up my leg and it must of stung me
Cause I was up all night itching nothing the doctors could anything but let it run its course

Boston

I've got a Woolly Bear in my back yard very short segments of black on either end and a long band of brown in the middle. Hopefully another mild winter in Boston if you believe. 9/13/16

We live i

We live i
n Indiana, central, we see all colors here black, white, brown, and striped soooo what does it mean????

saw a wooly bear with no black at all, only brown

saw a wooly bear with no black at all, only brown, what prediction would be made from this observation?

all-brown woolly bear

The Editors's picture

If it was truly a woolly bear caterpillar, larva of the Isabella tiger moth, then all-brown would mean a mild winter according to folklore. A nice prediction for the heating bill!

Woolly worms

The other day while taking my dog out to his outdoor surrounding, I saw a very black woolly bear on the ground. I live in SW PA.

I live in Lancaster and just

I live in Lancaster and just pulled about 30 off my tea. Some all black some all Brown/Orange some all white and some of various combinations of those.

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!

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.

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