Woolly worms: Forecasters or folklore folly?

I have heard it already: “I just saw a woolly worm, and it had a lot of black on it. Must be a harsh winter ahead!”

Almost everyone has heard the folklore about woolly worms — the darker and fuzzier they are, the worse the weather is supposed to be in the coming winter. Conversely, the more brown, orange or copper red, the milder the winter should be. What about this folklore? Should it be marked up as folly, or should we be bracing ourselves for a rough winter?

Woolly worms are actually called woollybear caterpillars. According to the Old Farmer’s Almanac, woollybear caterpillar lore began in 1948, when Dr. C. H. Curran, curator of insects at the American Museum of Natural History in New York City, began studying the caterpillars. Over the course of eight years he captured, measured and documented relative colors of woollybear caterpillars and tried to associate upcoming winter conditions with the color patterns. He would forecast the coming winter weather through a reporter friend of his at The New York Herald Tribune. Woollybear caterpillars became North America’s most recognizable caterpillar.

In recent years, Banner Elk, North Carolina, has hosted an annual “Woolly Worm Festival” each October, highlighted by a caterpillar race. Vermillion, Ohio also hosts an annual festival.

But, before we get too warm and fuzzy about festivals and folklore, let’s review some facts about woolly worms.

Notable Purdue entomologist Tom Turpin has written about these famous caterpillars. “The woolly worm featured in these festivals has the ‘official’ common name of banded woollybear,” he said. “The name is official because it is the one listed in the Entomological Society of America’s Common Names of Insects & Related Organisms publication.”

Turpin said there are other common names also used for this caterpillar, including black-ended bear and fuzzy wuzzy. This fuzzy caterpillar is called banded because it is black on both ends with a reddish brown band in the middle.

Woolly bear caterpillars, like other caterpillars, eventually turn in to a moth. In the fall, woolly bears crawl about looking for a suitable spot to hunker down for the winter. They pupate in the spring and emerge as moths.

“The banded woollybear is scientifically classified as Pyrrharctia isabella,” wrote Turpin. “Known as the Isabella moth, it is one of the so-called tiger moths.” These are medium-sized moths with a wingspan of about two inches; the moth is a dull yellow to yellow-orange with sparse black spots. They are usually conspicuously spotted or banded. The caterpillars of tiger moths are normally hairy, which is why they are known as woollybears or woolly worms.

Turpin said that the caterpillars feed on a wide variety of food plants found in many different habitats. Food plants range from hardwood trees to plantain — a common roadside plant and lawn weed. They are also an occasional soybean pest in Indiana.

What is it that affects the variability of those black and brown bands?

“There is some year-to-year variation in the amount of black hair on banded woollybears, but the differences are caused by age and wetness,” wrote Donald Lewis, Department of Entomology at Iowa State University, in 1994.

Carol Quish, University of Connecticut, wrote that the caterpillars molt several times during the summer and fall. “At each molt, a portion of the black setae (hairs) are replaced with orange/brown setae, making the middle sections longer,” she said. “So the older the caterpillar, the more molts it has gone through, therefore the less black areas and more orange/brown.”

So, how accurate is the brown-banded caterpillar of the Isabella moth in predicting the winter weather? “Not at all!” said Turpin. “It is folklore, pure and simple.”

There is one forecast you can count on, however — when you see woolly worms in the fall, winter will soon be upon us. Additionally, it will probably be cold at some point, and we may have some snow!

John Woodmansee is an extension educator in Whitley and Noble counties.

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