How Did A Fuzzy Caterpillar Become A Weather Forecaster? (2023)

The woolly bear caterpillar has long been associated with winter weather folklore. But why? And what does he turn into come spring? Find out!

by Amber Kanuckel Updated: September 27, 2021

How Did A Fuzzy Caterpillar Become A Weather Forecaster? (1)

The banded woolly bear, also known as the woolly worm caterpillar, is one of the “signs of nature” to watch to foretell the winter weather to come (he’s #18 on our list of20 signs of a hard winter). According to folklore, if the caterpillar’s orange band is narrow, the winter will be snowy; conversely, a wide band means a mild winter. And fuzzier-than-normal woolly bear caterpillars are said to mean that winter will be very cold.

How did these caterpillars become a winter weather forecaster? And what else do we know about them? While we only pay attention to them at one stage of their lifecycle, there’s much more to these furry weather prognosticators than meets the eye. Check out these interesting tidbits:

Why Do Woolly Bear Caterpillars Appear in the Late Summer and Fall?

As a caterpillar, the woolly bear is technically larva, which is the first stage of life for a moth or butterfly after it lays eggs. The eggs hatch in the fall, which is why woolly bear caterpillars are such a common sighting during this season. Though they are most common in the fall, early hatchlings can also be spotted during the summer months, too.

What Does A Woolly Bear Caterpillar Become?

Woolly bear caterpillars turn into the Isabella tiger moth (Pyrrharctia Isabella). You can recognize these moths by their yellowy-orange coloration, black legs, and small black spots on wings and thorax.

How Did A Fuzzy Caterpillar Become A Weather Forecaster? (2)

Woolly Bear Food, Habitat, and Lifecycle

Woolly bear caterpillars are known as generalist feeders, which means they will eat a wide variety of nature’s goodies, but they tend to favor leaves. Throughout the summer and fall months, they will feast on a wide variety of greenery from native plants —particularly herbs like dandelion, plantain, and nettle—but also tree leaves and other foliage.

While in caterpillar form, woolly bears tend to be nocturnal, eating at night and sleeping during the daytime, generally under fallen leaves or in other hidden spots. Of course, this isn’t always true, which is why we see these fuzzy caterpillars quite often meandering slowly about during the day.

How Did A Fuzzy Caterpillar Become A Weather Forecaster? (3)

As the weather turns colder, the woolly bear caterpillar goes into hibernation, choosing a sheltered spot in a fallen log, under a stone, or another good winter hiding place. Interestingly, these caterpillars might just be nature’s ultimate survivor—woolly bears produce a kind of antifreeze that protects their organs and other soft tissues while the rest of the caterpillar freezes solid over the winter. Because of this, they can survive temperatures as low as -90 degrees Fahrenheit!

When temperatures approach 50 degrees during the daytime in the spring, the woolly bear caterpillar thaws and starts moving around again, gorging itself on springtime greens like dandelions. As soon as they’ve eaten enough, they will spin a fuzzy cocoon — using their own fur, no less — and begin the transformation into their adult stage. Once a woolly bear has made its cocoon, which it will normally attach to grass or a twig, it will stay inside for somewhere between 10 to 15 days before emerging as an adult Isabella tiger moth.

(Video) Can Nature And Woolly Bear Caterpillars Be Simple Predictors Of Our Winter Weather Forecast?

So How Did Caterpillars Became Associated With Weather Forecasting?

How did the woolly bear caterpillar become a winter weather forecaster? These caterpillars and their ability to predict winter weather have been part of American folklore since the colonial era but were popularized by entomologist Dr. Howard C. Curran, curator of insects at the American Museum of Natural History in New York City, when he decided to put it to the test. In 1948, Curran headed to Bear Mountain, New York, to study the caterpillars and found that over half of his test subjects had wide orange bands, meaning the upcoming winter would be milder-than-average. And it was. He relayed his findings to a reporter and the story was published in the New York Herald Tribune.

Dr. Curran continued his study for eight more years but was never able to fully conclude whether the woolly bear was a reliable prognosticator. But the folklore continues to this day.

Are All Black Caterpillars Woolly Worms?

Caterpillars that are all black, all brown, or another color are a different species, not Pyrrharctia Isabella—so don’t think it means that winter will be brutal if you spot one!

Even though not everyone subscribes to the woolly bear method of weather forecasting, watching them in the fall is an exciting American tradition that is unlikely to change anytime soon. In fact, there’s even a famousWoollybear Festivalheld annually in Vermilion, Ohio that celebrates the caterpillar’s abilities.

Watch a woolly bear caterpillar make a cocoon (time-lapse)!

Our Predictions

We don’t use the woolly bear caterpillar or any other bits of folklore to make our predictions (here’s how we do it) and we just released our winter 2020-21 winter outlook. Here’s what we’re forecasting!

How Did A Fuzzy Caterpillar Become A Weather Forecaster? (5)


Amber Kanuckel

Amber Kanuckel is a freelance writer from rural Ohio who loves all things outdoors. She specializes in home, garden, environmental, and green living topics.


How do caterpillars predict weather? ›

The longer the woolly bear's black bands, the longer, colder, snowier, and more severe the winter will be. Similarly, the wider the middle brown band is associated with a milder upcoming winter. The position of the longest dark bands supposedly indicates which part of winter will be coldest or hardest.

What does Farmer's Almanac say about the wooly caterpillar? ›

The woolly bear caterpillar tells if it is a bad winter if there are a lot of them crawling around, if he has a heavy coat and if the black band on his back is wide. The more black than brown he is or the wider the black stripe, the worse the winter.

What does caterpillar mean in weather? ›

Orange segments predict mild weeks, and black ones foretell bad winter weather. Others also look at the thickness of the hair—thick means a bad winter ahead, and sparse means a mild winter. One more weather belief surrounding this tiny weather forecaster revolves around the direction it's coming from when found.

What does a black and orange fuzzy caterpillar turn into? ›

Description: The woolly bear is a fuzzy, orange and black caterpillar that becomes a dull, yellow to orange moth with a fat, furry thorax and a small head. Ecology: One of our most familiar caterpillars, woolly bears are renowned wanderers.

What determines what a caterpillar turns into? ›

Once the caterpillar is done eating and growing, there is a lack of the juvenile hormones, which causes the caterpillar to form a silk cocoon or shiny chrysalis around itself and begin radically transforming into a gorgeous butterfly. The cocoon is often hidden under branches, in a bunch of leaves or even underground.

What happens to caterpillars when it gets cold? ›

As it gets colder, the caterpillars slowly freeze, but the glycerol prevents their inner cells from freezing. This allows them to survive even the most extreme winter weather conditions. In fact, woolly bear caterpillars can survive at temperatures as low as 90 degrees F below zero.

How accurate is the woolly worm predict winter? ›

As much fun as it is to search for the woolly worm each fall, don't put your bets on it. The caterpillar can't predict what Old Man Winter has in store for the upcoming winter season. The caterpillar's coloring is thought to be based on its age, how long it's been feeding and its species.

What are the wooly worm predictions for 2023? ›

2022-2023 Woolly Bear Winter Prediction

So, this year the beginning will be worse, the middle not as mild, and the end about the same. Many of the Woolly Bear caterpillars we have seen this fall have dense hair. This is an indication the winter will be cold.

How accurate is the wooly caterpillar? ›

Dr. C.H. Curran, former curator of insects at the American Museum of Natural History in New York City, surveyed the bugs back in the 1950s. His studies showed that the woolly bear caterpillars had an 80 percent accuracy rate. However, today's entomologists say no one has been able to replicate the study.

What does the wooly caterpillar predict for the weather? ›

Woolly bear caterpillars—also called woolly worms—have a reputation for being able to forecast the coming winter weather. If their rusty band is wide, it will be a mild winter. The more black there is, the more severe the winter.

What does it mean when a caterpillar is all black? ›

Well, no. The Old Farmer's Almanac says: “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.”

What is the biblical meaning of seeing a caterpillar? ›

Biblical Meaning of Caterpillars

The Christian religion butterfly's biblical meaning is seeing the butterfly as a symbol of resurrection. The biblical meaning of the caterpillar in our dreams tells you about a complete transformation that will take place within your mind, body and soul.

What happens when a dog eats a caterpillar? ›

Oral exposures, while not common, are definitely possible and may lead to drooling, head shaking, pawing due to discomfort, gastritis, esophagitis, difficulty swallowing, enteritis and tongue, lip and oral irritation. Treatment for a pet exposed to a caterpillar is largely symptomatic and supportive.

What does a white wooly worm mean? ›

In case you didn't know, folklore says that thin brown bands on the woolly worms means a harsh winter is coming, wider brown banded woolly worms mean a mild winter, nearly black woolly worms means a severe winter is coming, and finally the very light brown or white woolly worms mean a snowy winter according to the ...

Why do caterpillars cross roads? ›

The second generation is the one noticed in late fall when the woolly bears are crossing the roads, usually in great haste as if they have someplace special to go. In fact, they are only scurrying to find a sheltered location under dead plant debris, etc., where they will spend the winter as a larva.

Can you tell what a caterpillar will turn into? ›

A caterpillar is a wormlike and often brightly colored or hairy or spiny larva of a butterfly or moth. It is nearly impossible to tell whether a caterpillar will turn into a moth or a butterfly without identifying the species of caterpillar.

How accurate is the woolly worm? ›

Still, even though scientists would prefer to not acknowledge the woolly worm it has a n 80 to 85% accuracy rate of predicting our winters, which is pretty amazing if we really think about it. So enjoy fall, have some fun with old folklore and try to predict winter.


1. The Myth of The Woolly Bear
2. Can Caterpillars Predict the Weather?
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3. Can a Woolly Bear REALLY forecast winter? Five Researched Facts! (Isabella Tiger Moth Caterpillar)
(Nature at Your Door Frank Taylor)
4. Furry Forecasters: Can Woolly Bear Caterpillars Predict Weather? #WoollyBearCaterpillars #funfacts
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5. Predict Winter Weather With The Woolly Worm!
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6. Can Woolly Worms Predict the Weather?
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