Thomas R. O'Donnell

The woollybear boogie: a fall trek of Lilliputian proportions

In Uncategorized on September 23, 2018 at 2:00 pm
A fuzzy forager beating multiple feet across a little-used blacktop in Van Buren County. See you hanging around my yard light next spring, little fella.

A fuzzy forager beating multiple feet across an Iowa blacktop. See you flitting around my yard light next spring, little fella.

If you drive the little-traveled county blacktops of rural Iowa, as I do, you’re sure to notice a slow (and sometimes not-so-slow) march at this time of year.

They’re easy to spot in the distance: small smudges inching across the blue-gray pavement. The contrast of dark on light and the steady movement draws the eye, making the sojourns of woollybear caterpillars hard to miss, even though they’re relatively tiny.

I saw countless fuzzy travelers on my trips through southeast Iowa one recent weekend. There seemed to be one every few yards, crossing the pavement and, with luck, avoiding the many tires that would halt their travels (and their lives).

What’s going on here?

In Iowa, there’s only one person to call for the answer: Donald Lewis, Iowa State University’s extension entomologist. Lewis has been at this since the mid-1970s and, as they say in the journalism business, gives good quote.

“One of the greatest jokes of my life without a punch line is ‘Why did the woollybear cross the road?’” Lewis said last week.

We’ll get to that, but first let’s be sure what we’re talking about.

I’ve noticed that some of the crawlers creeping across the roads are bigger and browner while others are smaller and blacker. That’s because there are about half a dozen species of what people call the woollybear caterpillar. (There’s some debate about whether it’s two words – woolly bear – and two Ls – wooly bear. I’m sticking with woollybear because it looks nicer.)

The best-known beastie is the banded woollybear, which sports a distinctive orange racing stripe around its middle. This caterpillar is the stuff of legend – weather-predicting legend that I won’t go into except to say that it’s bunk. (Lewis says the critter’s coloration has more to do with past weather than predictions for the future.)

Lewis says he often sees two other woollybear varieties: the salt marsh caterpillar (which, he notes, is a curious name given we don’t have salt marshes in Iowa), which can range from blonde (and has more fun) to black; and the yellow woollybear, which can be almost cream colored.

A woollybear’s summer, much like a teen-ager’s, is spent eating grass and weeds (the caterpillar, not the human youth). But about this time of year it feels the urge to seek a cozy place to hole up, Lewis says.

That’s one of the things that makes these sizeable squirmers (up to 2 inches long) different: Many woollybear species curl up in a protected location and wait out the winter before building a cocoon and transforming into a moth. Most other moth species transform before winter. (In fact, the banded woollybear produces a chemical that acts as a kind of antifreeze while hibernating.)

“Crossing the road is part of this wandering behavior to find someplace hidden,” Lewis said. Even the woollybear species that do pupate (spin a cocoon or become a chrysalis) in the fall are on the run at this time of year, looking for good place to make the switch.

“But of course they’re not going to stay hidden until it gets cold. As long as it’s a warm, sunny day they’re going to be wandering,” Lewis said.

I’ve noticed that some of these guys really haul, uh, abdomen across the road – maybe to avoid a set of Firestones barreling toward them. “I don’t think tires enter into their calculations or their behavior,” Lewis said, deflating my idea. “Before we make too much of their speed, we’re going to have to get down on the pavement to measure the temperature and see if is temperature-correlated. If not, we’ll have to come up with some other excuse for why some are fast and some are slow.”

For the woollybear, life as a caterpillar is the apex of their celebrity. They metamorphose into the Isabella tiger moth (Pyrrharctia isabella), “a plain, pale cream-colored moth that nobody notices,” Lewis said – or seeks out for weather forecasts. The salt marsh caterpillar (Estigmene acrea) becomes the salt marsh or acrea moth, a flashier white, orange and black creature, and the yellow woollybear becomes the white Virginia tiger moth (Spilosoma virginica).

The cadres of caterpillars you see cutting across that county road are only looking to get on with their short lives. So should we avoid crushing them with our Camrys and Cadillacs?

That’s a philosophical question, Lewis said. “Do you swerve to miss bunny rabbits, squirrels, turtles and snakes? Do you have respect for the interdependent web of life that we’re all a part of?”

He votes for avoidance – as long as he can do it safely. “I try to miss all living creatures with my car. If they’re not hurting me I don’t want to hurt them.”

Good advice.

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