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Out In the Woods – Feeding and Age Determine Wooly Bear ‘Forecast’

moth: Andy Reago & Chrissy McClarren caterpillar: National Weather Service

By Kevin McKeon, Maine Master Naturalist

We’ve all seen wooly bear caterpillars crawling around. “Where are you going? What kind of winter will we have? Your black band is smaller than your orange one, so what are you telling me? Why are you in a ball?” Let’s begin with folklore—and those colored bands.

The black bands describe the upcoming winter: long bands indicate a long, cold, snowy season. If it’s longer around the caterpillar’s head, the early winter will be more severe; at the tail means a late winter woe. A thick “fur” coat means a cold winter. If it’s traveling southerly, it’s escaping the severe cold coming from the north; moving northerly, a mild winter is coming. Look closely enough and you’ll notice that there are 13 segments making up its body…one for each week of winter!

These colonial-era myths blossomed in 1948, when Dr. Howard Curran, entomologist at the American Museum of Natural History, counted the bands on 15 specimens, his winter’s forecast was published in the New York Herald Tribune, then picked up by the national press: The rest is history!

Since 1973, Vermillion, Ohio celebrates the state’s largest one-day festival—The “Wooly Bear Festival”—hosting parades, caterpillar races, and “official” analysis of the color bands and fur…all leading up to the winter’s forecast proclamation. Banner Elk, North Carolina, trumpets their “Wooly Worm Festival”, with all-day worm races, and the fastest worm and owner not only being crowned, but paid! Pennsylvania, Kentucky, and even Ontario hold similar galas.

Now, for the rest of the story (and please don’t be dismayed!) …

The wooly bear’s coloring is mostly determined by its feeding and age. A rich food source makes for a fat, long caterpillar, with longer black bands along each end and a shorter orange band. And they shed their skin six times, each time becoming less black and more orange. Curling up and playing dead? They do it when disturbed, earning the Hedgehog Caterpillar moniker.

Marshes and meadows, their preferred habitat, hold grasses and other greens for the caterpillar to eat, and wildflower nectar to feed the adult moth, called the Isabelle Tiger Moth. The moth, after emerging from its cocoon and eating for a bit, will mate and lay eggs. After a few days, our furry friend emerges from its egg and begins eating almost anything green.

In temperate climates, there are two generations per year, and it’s the second generation we usually see, in late summer/fall, crawling around, looking for a place to overwinter under thick vegetation. As they enter hibernation (called diapause with insects) and slowly begin to freeze, their cells are protected by the formation of glycerol—a natural anti-freeze; many amphibians do this, too. Their setae, or fur, is there to help them regulate how fast they freeze! In the cold of the Arctic, they age much more slowly: they’ve been recorded to remain caterpillars for up to 14 years!

Awakened by early spring warmth, the caterpillar will eat for a short while, then search for a protected spot to form a cocoon. In late May/early June, the adult moth emerges to begin the life cycle of the next generation.

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