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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Here in waaaaayyyy Upstate

Here in waaaaayyyy Upstate New York on Vermont border we are just now seeing Wooley Bears for the first time this year. Alll so far have been even between black front, orange middle, and black rear. The "lore" I have always heard is that the segments predict how long each portion of the winter will be---front section is for Fall and Early winter; middle for mid winter and rear for end of winter shading in to spring. This does correspond with a harsh or mild winter if you think about it just not direct temperatures. Altho we have very few squirrels out here in Farm Country (go figure!) we have a bumper crop of black walnuts on yard trees and have seen LOTS of acorns on trees and ground. Have seen LOTS of foxes recently many more and with more fur than you would expect. More road kills than usual among all furry things---does this mean they are more active looking for food? And baby skunk in the daytime last week! Enjoying introducing very curious grand daughter to Wooley Bears and lady bugs etc but NOT so much the incredibly ANNOYING and prolific "Biting flies" that followed the recent flooding here. What is UP with THAT??????

I just saw a woolly bear ALL

I just saw a woolly bear ALL ORANGE with just alittle black band around face. What does that mean? I live in upstate NY

Hello, it might have been a

The Editors's picture

Hello, it might have been a different variety. According ro folkore, the narrower the brown (orangish) band on the woolly bear caterpillar, the more severe the coming winter.

I'm upstate as well, in the

I'm upstate as well, in the Finger Lakes area right near Lake Ontario. I have fou d 3 woolys that had a little black on head and tail and a big band of brown/orange. A friend of mine is finding the same. I haven't seen this much brown/orange on one in quite awhile. Livestock don't look too shaggy coated either.

I can only hope it will be mild, as I absolutely hate winter.

i have seen wooly worms this

i have seen wooly worms this year that are almost blond with no red or black bands. any idea what this means? i am in the laurel highlands in western pa

If by "blond" you mean the

The Editors's picture

If by "blond" you mean the lighter brown section, it means that the wider the middle brown section is (or the more brown segments there are), the milder the coming winter will be. Conversely, a narrow brown band is said to predict a harsh winter.

We are in So. CT near NY

We are in So. CT near NY border and just found a Wolly Worm that is about 50:50 brown and black. What does this mean for CT winter?

We are in southern ct and

We are in southern ct and just found a black and brown caterpillar that was evenly brown and black. What does that mean??

I have also been seeing a lot

I have also been seeing a lot of woolly bears here in central Ohio that are exactly half brown and half black. I am also curious as to what that means.

I found quite a few this year

I found quite a few this year that are all brown, one had a small segment on the front that was black. My neighbor also found all brown ones too. I live in Webberville, MI

Here in Toronto Ontario I

Here in Toronto Ontario I have seen off white and totally gray ones:-) Interesting! Two one the off white and the other one was silver gray.

Stay away from these, the

Stay away from these, the bristles are infectious.

All Black here in Salvisa. Ky

All Black here in Salvisa. Ky from North Carolina and have always seen striped in NC! I think the solid colors mean a solid winter!!

They are all black here in

They are all black here in Springfield Twp, NJ too. Have never seen them all black!

The Wooly I saw this week

The Wooly I saw this week appears to be all black but with a shadowing of rust color beneath the black.I had heard of the Wooly's predictions but had forgotten so now will see if we have a rough winter. We live in Michigans Upper Peninsula.

On my way home from work, I

On my way home from work, I have been seeing that wolly worm on the road and it was very black every time I have seen it and I am seeing it more and more. I live in Roughemont NC

I agree, all that I have

I agree, all that I have found here in North East Ohio, 2 miles from Lake Erie are also all black. Not boding well for a smooth winter at all.

I live in NE Ohio as well.

I live in NE Ohio as well. Just returned from a walk in the Metro Parks, saw several of them and they were more than half orange..... Although I was not at the lake but in the Chagrin area, I wonder why the difference in the same general vicinity... Still hoping for a mild winter!!

Fortunately, the woolly bear

Fortunately, the woolly bear caterpillar I had just found late last week was almost entirely reddish-brown, with hardly any black whatsoever. I sure could use a mild winter here in Northern Virginia. Last winter was hellacious, with a three foot snowfall in one weekend last February. I am soooo not looking forward to a repeat of that. Thank you ~ (•8-D

I live in Fayetteville, NC.

I live in Fayetteville, NC. Just saw a wooley worm for the first time! I had to look it up just to know what it was. I was so surprised at how big it was. I took pictures with my finger for comparison :) No brown/red at all. Completely black. It will be interesting to see what the weather is like here!

I live in Western NC about an

I live in Western NC about an hour west of Boone, NC. This year the Woolly Worms here are mostly black with very little red or either all black.

I live in the southwest part

I live in the southwest part of Virginia (the mountains) and I've seen two caterpillars, barely the tinest of black on each end and 99% brown/orange in the middle. Never seen one that wasn't striped at all---interesting to see what kind of winter this will be.

I have seen all black ones

I have seen all black ones then some with black on each end and brown in the middle. What does that mean?

“If they’re solid black, it’s

“If they’re solid black, it’s going to be a bad winter. I’m hoping for a bad winter,” said Dick Kilmer of Moscow.

Georgia wolly worms/bears are

Georgia wolly worms/bears are all orange this year as well.

NJ wooly bears are all orange

NJ wooly bears are all orange this year too! I thought I was imagining it, but then I found this article. I wonder what is going on?

Wooly bears, Acorns and ice

Wooly bears, Acorns and ice in the Northeast.

This year there are so many acorns I cant walk a step in the back yard without stepping on three. The wooly bears are all orange though. This combination usually means that when we have precipitation we will see little snow, a lot of ice and the winter will be longer than normal. We are collecting the acorns for the deer due to the ice build up on trees will make it nearly impossible for them to get a decent meal in late february. Signing off in the lower hills of the Berkshires

Here in S.W. Missouri, as far

Here in S.W. Missouri, as far back as when I first came here in 1965, all the old folks predicted the winter as to how black looking they were. When lighter, a mild winter, when dark, a harder winter.

Our wooly worms/bears are all

Our wooly worms/bears are all orange also! Here in central southern michigan. What does it mean?!

Our woollies have always had

Our woollies have always had thick dark bands on them. yesterday I saw two without a single band....they were both a dark orange, very furry and quite large. what does this mean for this winter in southern Wisconsin?

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