They’re all around us at this time of the year. But unlike cicadas or crickets, they’re silent. And they’re often mistaken for a small rock or piece of wood. I’m talking about the caterpillar stage of the Isabella Tiger Moth – commonly known as Wooly Bears.
By Bill Lawyer
They’re all around us at this time of the year. But unlike cicadas or crickets, they’re silent. And they’re often mistaken for a small rock or piece of wood. I’m talking about the caterpillar stage of the Isabella Tiger Moth – commonly known as Wooly Bears.
I first noticed one a few weeks ago on the deck off the back of my house. Even though I’ve seen them many times before over the years, my first thought was it was a stone that had somehow landed there.
It was only when I picked it up to put it back in the yard that I noticed it was moving.
It rolled up into a ball — a hairy – no, fuzzy – ball. Many species of moths have caterpillars with hair. But most, such as gypsy moth caterpillars, just have a sprinkling of hair with irritating chemicals to repel would-be predators.
The hair of the wooly bears, on the other hand, is more like soft, thick fur.
For the average resident there may not be anything odd about finding a furry caterpillar in October, but the scientists among us know this is not the norm.
Most moths and butterflies either fly south for the winter or spend the winter dormant, in the egg stage of insect metamorphosis. In this stage they cannot be killed by cold weather.
Through careful observation, field naturalists have learned that in spring the larval (caterpillar) stage hatches from its egg, and then goes through a series of molts through spring and summer.
Eventually, they then pupate, and finally emerge as adult moths. The adults then mate (in ways too complicated to explain here) and then the females lay eggs in the fall. And so the cycle continues.
For whatever evolutionary reason – perhaps to fool predators – the Isabella moths go through one and one-half stages each year. They overwinter as caterpillars, rather than eggs, and then metamorphize in the spring. They lay eggs in the summer, which make it to the caterpillar stage again in the fall.
The amazing part, as scientists have discovered, is how these soft-bodied caterpillars survive the cold. Here’s how biologists at the University of Western Ontario explain it:
“It [the caterpillar] literally freezes solid. First, its heart stops beating, then its gut freezes, then its blood, followed by the rest of the body. It survives being frozen by producing a cryoprotectant in its tissues. In the spring, it thaws out and emerges to pupate.”
The wooly bear caterpillars have fascinated people for many years.
Those people who look to nature to predict what kind of weather the coming seasons will bring have adopted the wooly bear to predict what kind of winter will be coming their way. Similar to the way people have used groundhogs (Punxsutawney Phil, notably) to forecast what sort of weather will occur from early February to the end of March.
In the case of the wooly bears, the prediction is based on the color of their fur. Most wooly bears are usually two toned – black with a brown band in the middle.
Legend has it that the thicker the brown band, the colder the winter will be.
No reputable entomologist would accept that, as studies show that even caterpillars from eggs laid by the same moth can have varying thicknesses.
After noticing the first wooly bear on my deck, I then encountered one in my basement, and one on the driveway by my garage. And those were found without even trying.
But if you want to see if there’s any truth to the weather forecasting theory, you now have a reason to go out and look for wooly bears – right in your backyard.
