Woolly Bear Weather?

Ever heard of Pyrrharctia isabella, commonly called the Isabella tiger moth?  Perhaps you know it better in its larval form: the banded woolly bear.  Tiger moths get their names from their bold, contrasting colors much like the stripes of a jungle cat.  We have approximately 250 species of tiger moths in North America, of which the Isabella tiger moth (and its larval form, the banded woolly bear) is but one type.

A popular insect in folklore, the woolly bear larva is black at both ends and reddish-brown in the middle.  It’s found throughout the United States, Mexico, and southern Canada and produces two generations of caterpillars each year (in May and August).  The second generation is the one we usually notice in late Summer or early Fall when the larvae scurry across roads to find sheltered locations to endure the harsh winter months.  They survive our winter freezes by producing a cryoprotectant in their tissues, a kind of anti-freeze common in numerous types of insects.  In the Spring, the caterpillars will feed quickly on dandelions, plaintain, and other herbaceous plants and then metamorphose into a moth with white or yellowish wings scattered with black spots.  Wingspan is about two inches.  With its dramatic colors, it is well-liked among all insect watchers, young and old, in both its larval and adult forms.

In weather-prediction folklore, inherited from Native Americans, if the woolly bear larva has wide black stripes at the ends of its body, then we’re supposed to have severe weather during the coming Winter.  Is this true?

From long ago, we’ve hunted for portents and predictors in the natural world to help us understand the cosmos.  During the Medieval Period, scholars employed a now-debunked “doctrine of signatures” to discern God’s intentions in the plant kingdom for human usage.  For instance, if a plant had leaves shaped like a heart, then the plant was examined for its cardiac cures.  If the plant was shaped like a fetus or showed leaves melded together, then it was studied for its aid for pregnant women and broken bones, respectively.  So might the woolly bear be helpful as a predictor for coming weather?

The short answer is emphatically, “No.”  Larvae produced in the same clutch of eggs can vary from mostly red to mostly brown or even black, invalidating any actual temperature-related trends that may be otherwise evident.  Width of the rusty-colored rings may only indicate the maturity of the larvae: how near the caterpillars are to full growth before autumn weather stimulates their search for winter shelter.  Alas, another myth debunked by those darn scientists!

But don’t tell this to the good folks in Vermilion, Ohio outside Cleveland.  Each September or October since 1973, they have celebrated the “Woolly Bear Festival” – claimed to be the largest one-day festival in the entire state – that includes a parade, costumes, woolly bear races, and a quasi-official analysis of the bear’s prognostications for the coming Winter.  Similar festivities now take place in Kentucky, North Carolina, and Pennsylvania.  Imagine: an entire community promulgating myth to advance their revenues.  References to the spineless nature of insects notwithstanding, this seemingly innocent effort sounds like some ham-fisted politician running for Congress!

Since ancient times, we’ve searched fruitlessly for easily recognized patterns in natural phenomena to predict weather.  Recall the old ditty, “Red at night, sailors’ delight; red in the morning, sailors take warning.”  In fact, the Farmers’ Almanac is full of these so-called patterns of prediction.  In continuous publication since 1818, the periodical alleges an 80-85% accuracy rate for its annual forecasts, using a “top-secret mathematical and astronomical formula that relies on sunspot activity, tidal action, planetary position, and many other factors.”  Of course, these claims are not corroborated by independent researchers or peer-reviewed scientific journals.  Given the popularity of the Farmers’ Almanac and other persistent myths in our culture, including some of the mind-numbing claims in recent political campaigns, it seems we’re wired genetically for the fantastic and too-often throw reality to the four winds.

As a scientist, I’m both fascinated and irritated by the all-too-frequent gullibility of our species, especially as we enter the second decade of the 21st century.  The next prevailing cultural myth?  Who knows?  Let’s throw a party, and I’ll consult my tea leaves.