Wooly Bears - the bug, the myth, the legend

Tim Iverson, Naturalist

(10/2022) The myth holds that the wooly bear caterpillar is some sort of meteorological prophet. As an insect seer they can predict the severity of the upcoming winter. The story goes that on a dark and stormy night …. Wrong story. The story goes that the amount of black fur on the caterpillar is proportional to the severity of winter. The more black fur found means the harsher the winter will be. Conversely, if the middle brown stripe is larger than the black portions than the winter will be mild. In addition, if the head portion is dark than the start of winter will be severe. Or if on the hand, the hind end is darker and/or longer than the end of winter will be especially harsh.

Legend also has it that you can discern Old Man Winter’s intentions by the direction in which they crawl. If the caterpillar crawls towards the south than expect a brutal winter. If they’re making their way north than it should be a fairly mild winter. If they’re going east or west than perhaps check your compass, look puzzled, scratch your head, and find another.

The wooly bear has been heralded as a prognosticator of winter weather since at least the colonial era here in the Americas. It wasn’t until 1948 though that the myth hit a fever pitch. Dr. Howard Curran, Entomology Curator of the American Museum of Natural History, went to Bear Mountain, New York. He took a quick weekend trip there with some colleagues, their wives, and a reporter. While there he collected fifteen caterpillars, and counted their brown bands. From this he made a prediction on the upcoming winter, and the reporter ran the story in the New York Herald Tribune. The story was picked up by national markets, which was the equivalent to going viral in 1948.

Now, mind you fifteen specimen samples is hardly considered rigorous science. My guess is that this guy took a weekend vacation trip with some buddies and their wives and needed a way to write off the trip as a business expense so he took 15 minutes of his time to find 15 caterpillars to make wild guesses about weather. That’s purely speculation on my end and a digression at the very least if not borderline to full blown libel. The point is the story took off and it’s been engrained into pop culture ever since. It’s grown so outrageously in popularity that festivals have even arisen around the notion.

Wooly Bear Festivals have sprung up in at least six cities across the U.S. and Canada to celebrate the psychic who is shrouded in Punxsutawney Phil’s shadow. Each festival sports their own flare and ceremonies, but a couple boast races. "Trainers" coach these little guys to race up strings to a finish line. The first one to cross the line is considered to be boss supreme of the worm world and will be the official wooly bear forecaster for the year. This is an awful lot of frenzy over a fuzzy worm, but the fiction isn’t half as interesting as the actual facts.

The wooly bear caterpillar is the larval stage of the Isabella Tiger Moth. The body has 13 segments total, some say they represent the 13 weeks of winter. The fur (it always goes back to the fur) is called setae (pronounced see-tee) and is what makes its survival of winter possible. The fur doesn’t keep them from freezing, it makes it possible. This fur helps them to freeze in a controlled manner, but hold that thought.

Once the wooly bear caterpillar hatches from an egg laid by an adult moth it will start life in the spring voraciously munching on plants like dandelions and nettles. It will continue to do this all through spring and summer. Once the warm air moves out, and the chill of fall settles in the wooly bear makes its way from feeding grounds to overwintering sites. They usually set out for places underneath logs, rocks, or dense brush that will provide protection from any unwanted disturbance. The cool turns to cold and this is where the fur kicks in. The caterpillar begins to hibernate. Once this begins their bodies produce a natural "anti-freeze" called glycerol, and they begin to freeze almost solid. They will freeze until everything but the inside of their cells is frozen. The setae will actually begin the freezing process on the outside of the body, away from the internal cells. This is less damaging to their bodies, and energy reserves aren’t taxed on healing as much when it’s time to thaw out and wake up. It will spend just a few more weeks in spring eating some more before it spins a cocoon and grows up into a moth.

The average total lifespan for these insects from birth to death is usually one to two years maximum. In the colder arctic climates though there just isn’t enough food to spurn the kind of growth necessary to mature. Most of these caterpillars will take as many as 13 or 14 years to complete their life cycle!

The great clairvoyant caterpillar legend is based entirely on fur coloration. The bottom line is that they have no soothsaying ability. The fur coloration has more to do with the current season or past season than any upcoming one. If it’s been a great growing season than they’re likely to have narrower orange bands in the middle. If it’s been a poor season than the opposite should be true. The coloration pattern is entirely dependent upon feeding, age, and species. These caterpillars will molt approximately six times before reaching adulthood. With each successive molt they get a little less black.

I know, I’m a buzz kill. There are, however, some instances though where fact is stranger than fiction. The ‘pillar party doesn’t need to end though. We can still marvel at the fact that this remarkable insect has carved out its niche in this world in an incredible way. So, when you begin seeing these little guys crawling across trails and roadways in search of winter homes you can definitively say that winter is on its way. Despite what the fur color indicates or the direction they crawl I’d still buy a coat.