Looking for a home: the mass migration of woolly bears

Harvest Moon

Fall is a time of change and transition.  Geese chevron the sky, crows gather in murders to head south, and the cool night temperatures have deer and moose are once again moving from the deep canopy of woods to fields.  Ravens and foxes roam  the back meadow, mowed earlier and now green with new grass and clover, hunting voles and mice that are equally busy gathering nuts and seeds for their winter cache. The roads are filled with harvesters and threshers, and antique tractors pressed into service gathering potatoes and broccoli. The solid green of the summer woods is bedecked in hues of red and gold and copper, and the leaves on the poplars shiver first gold then silver in the freshening winds. Everything is changing, but around the end of September, one peculiar pilgrimage, the likes of which we had never seen before moving here, takes place: the woolly bear mass migration to our garage.

Woolly bears are those fuzzy ebony and burnt orange caterpillars that look like short, plump pipe cleaners, and that have long been viewed as a predictor of winter’s severity. 
Common knowledge is that a narrow band of orange flanked by wider black bands on either end means heavy snows, while the plumpness of the fuzzy crawler measures cold.  The plumper, the colder. The Farmer’s Almanac, a bastion of folk wisdom, especially about weather, and published right here in Maine, often includes the findings of woolly bear watchers, generally with mixed results.  Of course, that esteemed publication warns that one should also consider the acorn fall and the subsequent squirrel activity along with the band width and plumpness of woolly bears.  It’s too cold here for either oaks or large populations of gray squirrels, so we have no way to confirm the woolly lore we see creeping around us

The only true study of how savvy the furry crawler is at predicting winter weather took place more than a half century ago when a curator at the American Museum of Natural History rounded up all the woolly bears he could find in the Hudson Valley north of New York City and began measuring the stripes.  The study took place over eight years, and what he concluded about the reliability of the folk knowledge seems to have been lost to history.  That hasn’t affected how people view these little crawlers, especially those of us who live in the far north and know that the weather can change in a heartbeat.  Any early warning of what winter is likely to bring and when is always welcome. It’s why we pay attention when they begin their march, and march it is.

About midday, they crawl from the thick green of the fall lawn, emerging a few at a time, and begin heading east, up the driveway, toward the garage. As the sun passes overhead, hovering for just the briefest of times near noon, the numbers increase, and the pace quickens. Phalanx after phalanx of woolly bears move with remarkable speed over the sun-warmed asphalt, right into the shadowy coolness of the garage, and there they slow down.    Not a dozen or even two, not a score, but more.  They come in pairs and solo until the entire driveway is covered with undulating little bits of black and orange, and a casual stroll around the house yields a hundred or maybe two.  They come persistently, day after day, seeking a winter home. 

The march of the woollies

We have long been familiar with woolly bears and their mythologized ability to predict the coming winter.  We are, after all, northerners, used to hearing and believing the knowledge and lore of those who came before us.  As children, we scooped the caterpillars into cupped hands and watched as they rolled themselves into tight little spheres of fluff, resting lightly in our childish palms, and today, the grandkids do the same.  That the woolly bears roll up into tight little balls and play dead like an opossum is particularly intriguing to little folks. As adults, the first sighting of a woolly bear sends a shiver of anticipation, both joyful and fearful, at the thought of the coming winter. Young and old, they intrigue us in the same way the garage, or perhaps I should say doorways, intrigue them. 

We do not know exactly what it is about the garage that attracts them, what their steady marching across the cooling ground means, and so we are left to speculate, piecing together perceptions and misperceptions of the behavior of woolly bears. Until I looked them up this year, we did not know what stage of life this is for them, how long they live, or even what they become. We simply know that they come, over and over again, in numbers that are astounding. Can there really be that many caterpillars in the world?

Bruce worries about them, fears that they will come into our winter-icy garage, find a crack in which to hide and, as he puts it, freeze-dry themselves to death.  He scoops them up and tosses them back onto the lawn, but they are relentless, single-minded, and in a very few minutes, they are back on the driveway, marching toward the garage.  We had long assumed that the woollies pupated into Monarchs – someone must have told us that at some time – and as we love butterflies both for their beauty and for their ability to help pollinate flowers and herbs, vegetables and fruits, we encourage them as neighbors.  Who lets their neighbors freeze to death?  With each year we have lived here, the numbers of woolly bears increased while the number of Monarchs did not. It was a mystery.

Woolly bears love cold climes, surviving, nay, thriving even as far north as the Arctic, and they are uniquely suited for chilly climes, and  they do not pupate into Monarchs.  Rather, the woolly bear is the larva of the Isabella tiger moth that, although a pretty enough moth, is no Monarch, and although I have nothing to which I can compare the journey it takes to become that moth, it seems to have an unusual life cycle. 

The woolly bear emerges in all its black and orange glory in the fall from an egg buried all summer in the soil, and then rushes about trying to find a place to overwinter. Some are plump and fat – two inches long, a half inch wide – and some are tiny, barely a half inch in length and thin, but all in search of shelter, it seems. That  means finding a spot where the caterpillar can safely freeze and lie undisturbed through the winter.   That’s right, the woolly bears literally freezes solid. What allows the caterpillar to do this is something called a cryoprotectant, which is a substance that keeps tissue from being damaged when it freezes.  It’s common in some species of Arctic and Antarctic fish.  In the woolly bear, freezing is a process. First its heart stops beating, then the gut, and finally the rest of the body, and there it is, freeze-dried woolly bear, and so it remains until spring.  It then thaws out and pupates before becoming the moth.  For some reason, our garage is an attractive location for their winter snooze and metamorphosis. 

We don’t see a lot of the moths, which leads us to believe they are probably good food for the tenants in the bat house fifteen feet up the utility pole, but the number of woolly bears that show up each year seems to continue to rise, and each one seems convinced the garage is the best place to be.  Even though we know they will not perish if they winter in the garage, Bruce still scoops them up and tosses them back on to the lawn, because he is tired of stepping on them or squashing them when he picks up a basket or bucket, toolbox or piece of wood under which the fuzzies have hidden, preparing for their winter sleep. And the caterpillars still turn around and march right back to the garage. Although their pace is slower as the temps get lower, they still stroll through open doors, squeeze in through tiny cracks, wiggle under the rubber jam of the overhead door, and queue up along the rear foundation.  They are so common and plentiful that even the dogs no longer take notice of the tiny black and orange undulating bodies and instead, step around them, more concerned with the red squirrels that have begun to dart back and forth across the road, preparing, too, for the coming cold when woolly bears will be a distant memory, along with the last glorious days of fall. And we too hasten our preparations, stacking wood, mulching the garden, planting garlic, canning green tomato pickles and apple sauce, all in anticipation of the long cold days ahead, taking our cues from the woollies who are so relentless in their fall preparations.