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  • J. Woken

Weather According to the Woolly Bear

Updated: Jan 8

As the cool autumn weather eases us into another winter the woolly bear caterpillars are out and about, inching across many a road in search of spots to hibernate the winter away. These fuzzy little creatures are more interesting than one might think, with a biology that makes them a local wild marvel and a history that offers them up as any old school outdoorsman’s winter preparation guide.

An all-black woolly bear (Isabella Tiger moth) caterpillar creeps across a sidewalk. / Jessica Woken

The banded woolly bear caterpillar is typically identified by the band of reddish-brown around its middle sandwiched by a black head and tail. This larval insect will emerge in the spring as the abundant and unimpressive Isabella tiger moth, that fuzzy, bland orange moth fluttering around springtime porch lights in almost annoying numbers. But, as unimpressive as the bug may seem, this caterpillar actually creates its own “antifreeze” (glycerol) within its body chemistry, enabling it to survive frigid subzero temperatures and even, if it so happens, a winter encased in ice! In addition, instead of spinning a cocoon made solely of silk like other species of caterpillar do, woolly bear cocoons are made largely using their own fur. Little fuzzy marvels, indeed!

A white woolly bear (Virginia Tiger moth) caterpillar munches on a leaf outside Cannon Falls Mayo Clinic, a cute but daunting predictor of heavy snows to come. / Jessica Woken

Each year I seek out the road-crossing woolly bears with anticipation. Not only are their first appearances a clear sign my favorite season (autumn) is fast approaching, but folklore says the size of the woolly bear’s band is a good predictor of the upcoming winter: more brown means a milder season, more black means a harder one. Some even claim that spotting pale yellow or white woolies indicate heavy snow and blizzard conditions lie ahead.


In light of that, my personal sightings this season have caused me some anxiety. First, I found an all-black woolly; days later, an all-white one. What does this combination mean in folklore land? A very hard, long winter, with heavier than average snowfall. Oy vey.


According to science, however, the bands of the woolly bear caterpillar have little to do with future weather and more to do with temperatures when they hatched and how old the caterpillars are. Woolly bear coats get more brown with each molting or shedding, which can happen up to six times before the insect reaches its final larval stage. Also, white or pale-yellow woolly caterpillars are technically an entirely different species from the banded variety: these will transform into the Virginia tiger moth, basically an all-white version of the rust-orange Isabella.


Hard-core believers in the woolly bears’ abilities claim the caterpillars can predict winter weather to a stunning 80% accuracy. Interestingly enough, both The Old Farmer’s Almanac and The Farmers’ Almanac tout that they, too, achieve 80% accuracy. The Old Farmer’s Almanac predicts that winter 2018-2019 will be milder than usual, with less snow than average. Their rival publication, The Farmers’ Almanac, is on the woolly bears’ side: They claim a harder, snowier winter is on the horizon.


Who can we trust? Old Farmer’s, Farmers’, or woolly bear wisdom? It won’t be until we spot the pileated woodpeckers and hungry robins (the avian signs of springtime) that we’ll be able to say for sure who will have predicted correctly.


Author’s Note: Look out for other fuzzy caterpillar varieties out and about right now in the local wild, including American dagger and white-marked Tussock caterpillars. But beware! Individuals with sensitive skin can acquire itchy, burning rashes from the stinging hairs of those furry guys. Sometimes it’s best to look and not touch our local wild friends.

Left: An American dagger moth caterpillar held hostage on a red Solo cup. Right: A white-marked Tussock moth caterpillar with its signature red head and row of thick, stinging tufts. / Jessica Woken


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