Woolly Bear Caterpillars and Weather Prediction

Using Woolly Worms for a Winter Forecast


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.

Then, again, you can always check the winter weather predictions in The Old Farmer’s Almanac!

Find out which other animals can predict the weather and learn how to tell the temperature from cricket chirps!


The 1999 Old Farmer's Almanac

Reader Comments

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Woolly bear in PA

We were out splitting wood and came across not one but two all black woolly bears. We live in south central PA almost near the MD line. This is the first time in my 50+ years ever seeing a pure black one and I've lived in a number of different states.

Wooly Bear

I found two Wooly Bears while kayaking on the Clackamas River yesterday. We were near Estacada and the caterpillars' brown segment was 1/3.

wooly caterpiller

i am in the north east and all my caterpillar are all white what does this mean

White wooly bear

I don't think it's the wooly bear we're talking about here. I saw a white one up at my Dad's house in Pocono Summit, two years ago in late summer. I let it walk onto my hand and looked at it's face. What a face! It had sporadic black bristles in what looked like a weird angry expression. Reminded me of the Seinfeld episode where Uncle Leo loses his eyebrows and Elaine magic markers new ones on him, except everyone that looks at him thinks he's angry. Mother Nature sure has a sense of humor sometimes.

Wooley Bear Catapillar

I found a Wooley Bear Catapillar today in Patterson WA. Looks just like the above photo. Black on both ends and rusty color in the middle. Maybe half and half.

Woolly bear catapillars

I saw two woolly bear Catapillar's in central New Jersey today and both were totally rusty color

Yellow Wooly Bear

Pale Yellow Wooly Bear (no black) spotted today in 90 degree weather in Columbus, Ohio. Haven't seen many Wooly Bear's at all compared to 50 years ago. This one seemed slightly larger than usual.

yellow woolly bear

Had one on my deck railing today in South Jersey.

All orange woolly worm

Saw two all orange/rust woolly worms today here in Southern Maine. No black stripes or tips.

Spotted in MN

The dog and I found a wooly bear this morning in the Twin Cities! The middle band took up about 1/3 of it's body, so I'm hoping he's right and the meteorologists' prediction of a tough La Nina winter are incorrect!

No wooly bears at all!

I haven't seen any wooly bears at all this year. I've seen 3 of the all-black wooly's... all were dead.
Where have all the wooly's gone?
I live in Western Massachusetts and am outside much of the time. Surely I would've seen at least ONE by now!

Wooly Bear Caterpillar

I saw one today 9-19-2017 in DuBois, PA crawling across my driveway that was totally black no brown at all. Sounds like a bad winter. We will see as winter comes and goes.

White Wooly Bear

Yesterday my cat found a new friend in the house crawling through the living room, an all WHITE Wooly bear! Saved him from the cats claws! Hope it isn't true what they say...

White Wooly Bear

What DO they say about the white wooly worms?
We are in Southwest Ohio (Cincinnati area).

white woolly worms

i live here in IL. central part. Effingham. We are called Crossroads of I-70 and I-57.
We also have seen the while Woolly Worms. Did anybody ever answer you about
what it meant? Usually they say, the darker, colder and more precept but, never said
what white was.

Oregon sighting

Found one crawling on my deck tonight in Albany, OR. Less than one third was brown.

wooly bears

Yesterday l rescued (from my cat) what looked like a wooly bear but it was solid black. Could be a different species? Or should I head south for the winter?

Solid Black Woolly Bear

Yes, you may occasionally see the caterpillar of related species, like the Giant Leopard Moth, which are solid black in appearance! Fortunately, they don’t signal a harsh winter ahead. (Though we would still recommend heading south.)

Wooly Bear

I saw an insect that looked like a wooly bear but it's hairs were long. It kind of looked like a flannel moth caterpillar but same color pattern. As wooly bear.

Wooly Bear

I mean a caterpillar, not insect


Hi Becca,

The Yellow Bear Moth caterpillar and Virgin Tiger Moth caterpillar can sometimes have color patterns similar to wooly bears. The difference between these look alikes is that the Yellow Bear and Virgin Tiger caterpillars have longer, non-bristly hairs than Wooly Bears, which have shorter, bristly hairs. It’s possible the caterpillar you saw was one of these look alikes. 

Wolly caterpillar

I have seen three two of them we're just black tipped short the other was all brownish I'm 74 years old and I've been watching them since the late forties Central New York

Found this huge black fuzzy

Found this huge black fuzzy with orange skin in Ocala Fl while tending my monarchs and milkweed today!

white fuzzy wuzzy

so what would a creamy white fuzzy wuzzy mean?????

creamy white fuzzy wuzzy

The creamy white fuzzy caterpillar is likely a different species than the banded woollybear (or woolly worm), which can appear dressed in fuzzy black with an orange belt around the middle, or it can appear all black or all orange. The larva of the Isabella tiger moth, this caterpillar is the one normally associated with folklore about 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. Unfortunately, I don’t know of any “official” folklore that links white or cream fuzzy caterpillars to winter predictions, although some people suggest that their appearance might mean lots of snow to come.

Black Wooly Bear

I spotted a huge, beautiful black wooly bear this morning in a Tampa Bay!

Wooly Worm

Just found a solid black Wooly Worm on the back
porch in Hampstead North Carolina

Can a Woolie bear caterpillar be yellow in color?

It looked like a woolie bear to me! It had the long hairs and real slow movement but it was yellow in color on the body and the hair seemed white! Was it a baby woolie bear? Please comment if you know what this caterpillar is! Thank you! Jamie S, East Fishkill, NY

Yellow Woolly

I guess the answe would be yes as I just found an all yellow one in Western NC.

Little Bear moving through the garage

I walked out into the garage today and found a solid black woolly bear moving through the garage. I was surprised to see him inside, it's a first and this early in the year. We just relocated and was happy to see him of course. I guess it is time to ensure we have plenty of fire wood, blankets, groceries and prayers for winter.