Woolly Bears

A Woolly Bear caterpillar-www.bugguide.net-in A Garden For All by Kathy Diemer https://agardenforall.com

A Woolly Bear caterpillar (photo credit: www.bugguide.net)

According to folklore, a bristly, brown and black bottle-brush textured caterpillar may be able to determine whether we will have a severe or mild winter, simply by displaying more or less of one of its two colors.  More brown, a milder winter, more black, a harsher, longer winter.  How is it that we give such credence to a two inch long fuzzy slinky, and where did this legend come from?

Woolly Bear caterpillar-organicgardening.com-in A Garden For All by Kathy Diemer https://agardenforall.com

Woolly Bear caterpillar (photo credit: organicgardening.com)

To find out more about the curious little calico caterpillar, commonly known as a woolly bear, and scientifically called Pyrrharctia isabella (the Isabella Tiger Moth), I consulted with The Farmer’s Almanac (www.almanac.com), which dates back to 1948, when Dr. C. H. Curran, an insect curator of The American Museum of Natural History, traveled 40 miles to Bear Mountain State Park to collect as many woolly bear caterpillars as he could in one day.  Over the next eight years, Dr. Curran continued experimenting, trying to prove that the portion of reddish-brown segments on the woolly bear could forecast the coming winter weather.  Although Dr. Curran understood that his findings were inconclusive, he and his friends had great fun during the process, even calling themselves the Original Society of the Friends of the Woolly Bear. Regardless of the scientific outcome, woolly bears have become one of the most recognized caterpillars in North America.

Travelling Pyrrharctia isabella caterpillar-franklincountymgs.com-in A Garden For All by Kathy Diemer https://agardenforall.com

Travelling Pyrrharctia isabella caterpillar (photo credit: franklincountymgs.com)

And Pyrrharctia isabella’s popularity doesn’t end there, for there are Woolly Bear Festivals held every year (dating back to the 70’s) to celebrate this furry caterpillar, from Beattyville, Kentucky, Banner Elk, North Carolina, Vermilion, Ohio, Lewisburg and Oil City in Pennsylvania, and Lion’s Head, Ontario.  Banner Elk’s 25 caterpillar race results in a $1,000 first prize, along with the “prestige” of having your worm used to pronounce the official winter forecast . . . not a bad take for a lazy afternoon.  The Beattyville Woolly Worm Festival doesn’t say what the grand prize is for the fastest woolly, but claims to have over 110,000 visitors to their fair each year.  So, these events are no laughing matter to the towns that host them, and I wonder how often the chosen caterpillar makes a correct weather prediction?

Pyrrharctia Isabella Moth-Wikipedia-in A Garden For All by Kathy Diemer https://agardenforall.com

The golden Pyrrharctia Isabella Moth (photo credit: Wikipedia.com)

But seriously, what’s the scoop on these scruffy little two-toned critters that wander onto our lawns, decks, driveways (etc.) in mid-autumn, disappear in winter, and re-emerge in spring? The true woolly bear is the larval form of the Isabella Tiger Moth (Pyrrharctia isabella) and can be found in many cold regions, from northern Mexico throughout the United States and across the southern third of Canada, including the Arctic. The banded woolly bear larva emerges from the egg in the fall and overwinters (under bark, inside cavities of rock or logs) in its familiar caterpillar form, when it literally freezes solid. It survives this frozen state by producing a cryoprotectant (similar to antifreeze) in its tissues. In the spring the woolly bear thaws out, emerges to pupate (prepares to become a moth inside a fuzzy self-spun cocoon) and a few months later makes its final appearance as Pyrrharctia isabella. Although not too stunning as moths go, the medium-sized Isabella Tiger Moth, with yellowish-orange wings flecked with black, has only days to find a mate!

Pyrrharctia isabella caterpillar-Wikipedia.com-in A Garden For All by Kathy Diemer https://agardenforall.com

Pyrrharctia isabella caterpillar (photo credit: Wikipedia.com)

Like most insects, woolly bears progress through four stages in their life: egg, larva, pupa and adult.  Contrary to popular belief, hatchlings from the same clutch of eggs can display considerable variation in their color distribution, with black bands at the ends, and a brown center band which tends to grow with age, negating the common understanding that the colors remain consistent throughout the caterpillar stage. Their body is made up of 13 distinct segments, and some traditional forecasters say that the 13 segments of the caterpillar’s body correspond to the 13 weeks of winter. Woolly bears don’t actually feel much like wool, instead quite prickly with short, stiff spikes of hair. And handling them is discouraged, because the bristles may cause irritation for people with sensitive skin (they will often play dead if you pick them up anyway). They feed mostly on weeds, including dandelion, clover, and grasses, and generally will not harm your ornamental plants or vegetables. Overall, they’re a likeable enough critter and who’s to say if they really can foretell our weather tendencies . . . although I hope not, because the last one I saw was solid black . . .


  1. I had no idea woolly bear caterpillars were SO popular! They have a Big job on that little body….

  2. Hi Kathy, I have enjoyed all your latest posts. It is amazing how you come up with these different stories. Particularly loved the wooly bear. The information you give is wonderful! Mom

  3. Hi Aunt Kathy,
    I loved learnin about these cool critters.
    I had NO idea how cool they are.
    I hade a GREAT time looking at all
    These things ( but this is my favorite thing)

    • Why thank you, Lilly! Keep visiting because I’ll be talking about cardinals and turkeys and horses in upcoming posts. XO~

  4. Lillian Christen Bier says:

    Thank u for the info. My daughter caught one of these in our yard and put the little guy in a large mason jar. She included a handful of grass & a stick. In place of the metal lid, she used a plactic lid and punched out some holes. We put him in the kitchen window where the isn’t any direct sunlight & the temp would be the coolest. That was 3 days ago. But when we woke up this morning, he was gone & in his place was a fuzzy looking cocoon!!!! My daughter was so excited & i was pretty suprised myself [ i really wasnt expecting it to survive 🙁 ]. She started asking me all these questions which I had absolutely no answers for. Now, after reading this, I do. I like how ur article is such a fun, quick & easy read while also being full of information. Thank u!
    Lilly B.

    • I am so glad you and your daughter enjoyed the article! I try to take lots of technical info and consolidate it into bite sized tidbits of fun information that can be enjoyed without having to overthink it. Thank you for writing, Lillian. Please visit again ~

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