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.

 

Woolly-bears on the move

 

A Woolly-bear (Pyrrharctia isabella) crosses a road. I saw many of these well-known caterpillars last Sunday. The temps were in the low to mid 40's F, but it was sunny, and the bears were on the move.

I was at the Wilds and vicinity in Muskingum County, Ohio, mostly looking for birds to photograph. But wandering larvae temporarily side-tracked my quest.

I did shoot some birds, including this Northern Mockingbird (Mimus polyglottos). He was nestled in a shrubby thicket, but when I stopped for a look, he popped out to look back. Mockingbirds are extremely in tune with their surroundings, from my experience, and pay close attention to detail. Far more than most songbirds, it seems. Perhaps this behavioral characteristic aids them in carefully listening to and learning the songs and sounds that they mimic so well.

Anyway, after about ten minutes of watching the mockingbird, hoping for an interesting flourish of the wings or something else of note, I was rewarded. The bird suddenly flew down to the road and seized a Woolly-bear that had wandered onto the pavement. Yes! But my hopes for photo documentation were soon dashed when it flew into the heart of the thicket to deal with its prey. I could not see how he dealt with the larval bear and all its stiff bristles, but I imagine it sliced it open with that stout bill and slurped out the innards. Baltimore Orioles (Icterus galbula) successfully feed on spiny Eastern Tent Caterpillars (Malacosoma americana) in this way.

This was the first time that I've seen a bird prey on Woolly-bears. Their dense coat of bristles probably is a pretty good bird deterrent, most of the time.

A Giant Leopard Moth caterpillar (Hypercompe scribonia) crosses a road not far from where the mockingbird grabbed the Woolly-bear. I saw many of these, too, although the Woolly-bears outnumbered them by a good margin. This caterpillar is somewhat larger and thicker than the Woolly-bear, all black, and when seen well the reddish-orange bands delineating its abdominal segments are diagnostic.

I suspect that Giant Leopard Moth cats are frequently mistaken for "dark" Woolly-bears". As you may know, there is a pervasive myth that the darker the Woolly-bear, the tougher the coming winter will be. However, any analysis of that myth would have to somehow take into account the problem with caterpillar misidentifications. There is yet another very common species of tiger moth, the Virginian Tiger Moth (Spilosoma virginica) whose caterpillars can be active into late fall. Its caterpillars are known as Yellow Bears (it isn't rare for adult moth species to go by a different common name than their caterpillars). Yellow Bears are variable in coloration but often resemble very pale Woolly-bears. Such larvae, when misidentified as they almost certainly commonly are, would be "light" Woolly-bears that forecast a mild winter.

This is what a Woolly-bear becomes, if not eaten by a mockingbird, Buick'ed while crossing a road, or bumped off in some other way. The Isabella Tiger Moth, a handsome insect. While legions of people know the caterpillar, probably very few would recognize the moth that it transforms into.

This is a Giant Leopard Moth, a truly stunning species and always a crowd-pleaser. A leopard in mint condition is an entomological work of art, with its array of black circles and iridescent blue markings. Press one gently with your fingers, and it may "reflex bleed": exude two amber droplets from the front of the abdomen, just above the head. It's a very cool effect, and the droplets presumably are toxic and assist in warding off predation by birds.

Woolly-bears make bad meteorologists

Ah, the Woolly-bear, Pyrrharctia isabella, America's most beloved caterpillar. The tubular little beasts are impeccably zoned into neat patterns of burnt-orange and black, making for a darn good-looking larva. Woolly-bears are also undoubtedly the most widely recognized of North America's thousands of species of caterpillars, and that's due to their supposed ability to prognosticate the coming winter weather. The wider the orange band, the milder the winter, so the folklore goes. If that were true the bear in this photo would be calling for a balmy winter.

Not to burst any bubbles, or cast aspersions on any of the Woolly-bear festivals that have sprung up (one in Vermilion, Ohio - the "Woollybear Festival" - began in 1973), but there is no credibility to the caterpillars' role as weather forecaster. The widths of the colored bands are unrelated to future weather. Their size is much more aligned with their age. Caterpillars grow through various stages, each termed an instar. Five instars/stages is a common number of growth phases for most of our caterpillars. As they grow, and shed their "skin" between instars, caterpillars often change appearance markedly. In the case of the Woolly-bear, the black bands widen with age, and thus older caterpillars are darker. Dark old specimens might lead one to believe a brutal winter is on tap.

Get any sort of semi-warm snap, especially with sun, this time of year and out come the bears. It is very common to see Woolly-bears legging it across roadways under such weather conditions in early winter. I was able to stop at a few interesting places on my way to Canton last Wednesday afternoon, and saw numerous bears crossing roads. The temperature when I made this photo was only about 40 F.

For reasons unknown, Woolly-bear caterpillars are inveterate wanderers in fall and early winter. It doesn't seem to make much sense, as these caterpillars can eat an enormous variety of very common plant life, so there would seem to be little reason to risk the numerous threats that come with roaming far and wide. But nomads they are, and they know better than we what they are supposed to be doing.

The issue of the Woolly-bears' alleged skills as winter forecasters is also muddied by misidentifications. Unfortunately, not all people pay close attention to detail (just watch Fox News for proof!), and as distinctive as Woolly-bears are, there are similar species. The one above is a Giant Leopard Moth caterpillar, Hypercompe scribonia, and it too wanders widely in late fall/early winter. Some people will see one of these and instantly think the White Death will soon be upon us.

Another common ground-roaming fall caterpillar is that of the Virginia Tiger Moth, Spilosoma virginica, which is known as the "Yellow Bear". Were a true Woolly-bear believer to see this one, its nearly solid yellowish color might convince them that winter is slated to be quite Floridian.

This one, believe it or not, is another "Yellow Bear", but it might be better termed a Black Bear. The caterpillars of Spilosoma virginica are incredibly variable in coloration, and thus this one species is capable of fooling lepidopteran-illiterate Woolly-bear fans into believing the upcoming winter will be incredibly brutal, or unnaturally balmy.

Free-ranging Woolly-bears face great hazard when attempting to cross roads hundreds of times wider than they are. The mortality is high, but fortunately Woolly-bears are abundant. Vehicular carnage seems to dent their population very little. If they do make it to the other side, the bear will seek a sheltered spot to overwinter. That's right, this species rides out the winter that it is supposed to be forecasting as a fully grown caterpillar. The Woolly-bear can essentially freeze solid, and cryoprotectant chemicals in its system prevent irreparable damage to its vitals.

If all goes well for the Woolly-bear, come spring and warmer weather it will pupate and later emerge as this gorgeous moth, the Isabella Tiger Moth. I suspect very few people would recognize the moth, even though vast numbers of them would instantly identify the caterpillar.

Woolly-bears: fuzzy forecasters

A "woolly-bear", possibly the most recognized caterpillar in these parts. It's the larva of the Isabella Tiger Moth, Pyrrharctia isabella. Countless thousands of people can instantly recoginze the caterpillar; probably only a minute fraction of a percent could identify the moth.

This has been a boom year for moths and butterflies, and you can count in the woolly-bears. I've already seen scores of them, mostly crossing the roads, and many others are reporting lots of the little tubular fuzzies. Woolly-bears are stricken with a wanderlust in late fall, and that's why we see them roaming far and wide.

A well-known old wive's tale has it that the severity of the coming winter can be forecast by the woolly-bear's stripes. A big wide brown band and it'll be a mild one. Mostly black, and the bear is telling us we're in for a frigid winter. The bear above, being dominated by brown, is indicating an easy winter to come.

We'll see.