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Myth Buster: Woolly Bear Caterpillars Don't Predict Winter Weather

Have you ever been told that woolly bear caterpillars can tell you how bad winter will be? These caterpillars are the fuzzy black-and-brown insects that are often seen this time of year, but can they predict the coming winter weather?

Woolly bear caterpillars are often seen during fall, but they don't predict winter weather. (Photo via Shutterstock)

According to folklore, you can tell how bad of a winter you are in for just by looking at a woolly bear caterpillar. Legend has it that the longer the caterpillar's black bands are, the worse winter will be. If you see one with a wide brown middle band and small black bands at the ends, it means we will have a mild winter.

This doesn’t seem like a very scientific way to predict winter weather, and it isn’t. It turns out that the appearance of a woolly bear caterpillar doesn’t tell us anything about the winter weather ahead.

Fall is the time of year when we start seeing woolly bears. This is because they are leaving the areas where the plants they eat are to find dark, sheltered places where they can hibernate for the winter.

The color of their bands has nothing to do with the upcoming winter. Instead, the variation in a caterpillar's bands has to do with its species, age and feeding habits. There are many different species of these caterpillars, and the colorings and markings vary among the different species.

In good growing seasons, woolly bear caterpillars grow larger. This means the caterpillars will have narrower rusty brown bands and longer black bands. The colored bands can also tell us a little bit about how old the caterpillars are. Woolly bears molt six times before they are fully grown. With each molt, their bands change, becoming more brown and less black with age.

This popular, weather-predicting myth isn't the only one connected with woolly bears. Some people believe that the direction the caterpillars are seen traveling in fall also tells us about the winter ahead. Caterpillars traveling south are said to be trying to escape the cold winter ahead. If you see a woolly bear caterpillar traveling north, it is said to mean a mild winter. And some people grew up being told that the hairier or woollier these caterpillars appear, the worse the winter will be. As you might expect, there's no truth to any of these myths.

While nothing about these caterpillars can tell us about what kind of winter we will have, they do have a unique way of surviving even the coldest winters. They produce a substance called glycerol, which works in their bodies like antifreeze keeps your car’s engine from freezing. As the weather turns colder, the caterpillars slowly freeze, but the glycerol prevents their inner cells from freezing. This lets the caterpillars survive even the most extreme winter weather.

For many people, woolly bears are one of the few insects many people know by name. But they actually go by many names. Their most common name is woolly bear caterpillar, but they are also called fuzzy bears or woolly worms. Some people call them hedgehog caterpillars, because they sometimes roll up into a ball and play dead if disturbed.

And while many people can easily identify these insects in their larval state, not many people know what these caterpillars grow up to be. Woolly bears turn into Isabella tiger moth caterpillars, an orangish-yellow moth that's active on summer nights.


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