Nature: Wandering woolly-bears well known, but can they predict the winter weather?

A woolly-bear crosses a road in Muskingum County/Jim McCormac

NATURE: Wandering woolly-bears well known, but can they predict winter weather?

Columbus Dispatch
January 2, 2021

NATURE
Jim McCormac

On Dec. 12 of last year, I headed to remote areas of Muskingum County. Bird photography was my primary goal. The sun shone brightly, but it was a seasonally apropos 43 degrees for a high.

Especially alluring was a gorgeous northern mockingbird occupying a dense thicket. He was as interested in me as I was in him and popped out to closely scrutinize me. Mockingbirds are far more inquisitive than most songbirds and pay close attention to their surroundings.

His behavior allowed for great photo ops. Suddenly, the mocker dropped to the nearby roadbed and seized a woolly-bear! This is the first time I can recall seeing a bird take one of these heavily bristled caterpillars. Unfortunately, the bird shot into the thicket’s innards with his prize, and I could not see how he dealt with the larvae and its coat of spiky hairs.

The mockingbird tipped me to watch the roads more closely. I ended up seeing dozens of woolly-bears, and many giant leopard moth caterpillars (Hypercompe scribonia), which look similar.

Woolly-bears are perhaps North America’s best-loved and most familiar caterpillar. They are often noted — and frequented smashed — as they wander across roads. They can be active in very cool temperatures, especially if the sun is out. I’ve seen them wandering in temperatures in the mid-30s.

A woolly-bear is the immature stage of the Isabella tiger moth (Pyrrharctia isabella). The moth is quite attractive: creamy-yellow and burnt-orange, and sparsely peppered with black dots. In spite of its good looks, hardly anyone other than a lepidopterist would recognize the moth. But everyone from elementary school kids to the mailman knows the fuzzy, banded caterpillars.

One reason that so many people know them is because woolly-bears are abundant. The second of two broods of caterpillars hatch from eggs in late summer or fall, and the mature larvae seek sheltered nooks with the coming of cold weather. Once ensconced in its winter sanctuary, the woolly-bear will ride out the winter months and form a cocoon come spring.

But if it gets warm enough, the larval bears rouse themselves and wander, even in mid-winter. They are provisioned with nature’s version of hand warmers, chemicals known as cryoprotectants. These solutions allow the caterpillar to endure temperatures so cold that it becomes a larval popsicle, yet not suffer tissue damage.

It has long been held that woolly-bears are weather predictors: they foretell the severity of the coming winter. Legend has it that the wider the light-brown center band of the caterpillar, the milder the coming winter. Blacker caterpillars are an omen of a long severe winter.

Charles Curran, curator at the American Museum of Natural History, studied the woolly-bear band width theory between 1948 and 1956. He, his wife, and several acquaintances would make annual fall foliage trips to the area of New York’s Bear Mountain State Park, where they also encountered scores of woolly-bears. Curran kept fastidious notes on woolly-bear coloration in an attempt to link them to weather patterns.

Curran and his allies jokingly formed the Original Society of the Friends of the Woolly-bear. His larval weather correlations were inconclusive, and caterpillar forecasting can probably be put in the same league as that of groundhog Punxsutawney Phil and his winter-ending shadow.

Further throwing a wrench into woolly-bear weather-predicting is the issue of misidentifications. Giant leopard moth caterpillars also overwinter, are commonly seen roaming about, and greatly resemble black (bad winter) woolly-bears.

Yet another caterpillar active into early winter is the yellow-bear, the larva of the Virginian tiger moth (Spilosoma virginica). It looks like a pale woolly-bear, and thus a predictor of a mild winter.

Naturalist Jim McCormac writes a column for The Dispatch the first and third Sundays of the month. He also writes about nature at www.jimmccormac.blogspot.com.