Does a Woolly Bear Caterpillar Predict Winter Weather?

In the caterpillar world, few are as well-known as the woolly bear (sometimes known as a wooly worm). While monarchs caterpillars surpass them in name recognition, they’d take an easy second place. After all, while people might not know what they’re called or what they turn into, a decent percentage of folks have at least spotted a woolly bear. Many of those same people might also point to the caterpillar and make a prediction about winter based on its appearance — but is that prophecy? Is it a myth? Here’s what to know about these familiar, fuzzy creatures.

Woolly Bear Caterpillar Weather Predictions: Fact or Fiction?

Legend claims the size of a woolly bear’s black and brown stripes can predict a harsh winter. Some folklore even breaks it down by the length of each black stripe.

• The longer the caterpillar’s black stripes, the colder the winter
• When the caterpillar’s brown fuzz takes up most of its body, there’s a mild winter ahead
• If the longer black stripe is by the head, the first half of winter will be colder
• If the longer black stripe is by the caterpillar’s lower half, the second half of winter will be colder

That’s a whole lot of predictive weight to place on a single caterpillar!

If you’re raising your eyebrows, your skepticism is warranted. As is the case with many such claims, woolly bear caterpillars don’t really predict the harshness of an upcoming snowy season.

The differences in coloring result from differing molts. So, while observers might notice discrepancies from one woolly bear to another or different stripes on the caterpillar’s bodies, this has to do with the caterpillar’s life cycle and the resources available to it. Milder conditions with abundant food usually causes caterpillars to have wider brown bands.

Where Do Woolly Bear Caterpillars Live?

While they don’t foretell of warm or cold winters, woolly bears are still beloved across the country. Multiple places in North America (including Canada!) host woolly bear festivals to celebrate these tiny creatures.

How Do Woolly Bears Survive Winter?

Woolly bears overwinter under leaf piles, logs, wood piles, and in other cozy places. Their ability to survive cold is incredible: according to the National Weather Service, they can survive temperatures approaching -90 degrees Fahrenheit, and they’ve even survived overwintering frozen in an ice cube.

Their bodies produce glycerol, a substance that keeps the caterpillar’s most vital cells from freezing when the weather gets bitterly cold. When the weather warms, the caterpillar then emerges from “hibernation.”

Does a Woolly Bear Caterpillar Turn Into a Butterfly or a Moth?

In spring, the woolly bear spins a cocoon and transforms into the Isabella tiger moth. These moths appear throughout summer, when they lay eggs — and the woolly bear cycle begins again.

Sources

• National Weather Service, “Woolly Bear Caterpillar: Winter Predictor, Or Not?“
• Mass Audubon, “Why Did The Woolly Bear Cross The Road?“
• The Forest Preserve District of Will County, “Why Don’t Woolly Bear Caterpillars Freeze to Death?“