Can Woolly Worms Really Predict the Winter Weather?

Legend has it that the woolly worm, a tiger moth caterpillar, can portend what weather winter will bring. In the fall, people look for wandering woolly worms to determine whether winter will be mild or harsh. How much truth is there in this old adage? Can woolly worms really predict the winter weather?

What Is a Woolly Worm?

The woolly worm is actually the larval stage of the Isabella tiger moth, Pyrrharctia Isabella. Also known as woolly bears or banded woolly bears, these caterpillars have black bands at each end, and a band of reddish-brown in the middle. The Isabella tiger moth overwinters in the larval stage. In the fall, caterpillars seek shelter under leaf litter or other protected places.

The Legend of the Woolly Worm

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Woolly Worms: The Original Winter Weather Outlooks

By Tiffany Means

According to folk wisdom, when the brown bands on fall woolly bears are narrow, it means a harsh winter is coming. The wider the brown band, the milder the winter will be. Some towns hold annual woolly worm festivals in the fall, complete with caterpillar races and an official declaration of the woolly worm's prediction for that winter.

Are the woolly worm's bands really an accurate way to predict the winter weather? Dr. C.H. Curran, former curator of insects at the American Museum of Natural History in New York City, tested the woolly worms' accuracy in the 1950's. His surveys found an 80% accuracy rate for the woolly worms' weather predictions.

Other researchers have not been able to replicate the success rate of Curran's caterpillars, though. Today, entomologists agree that woolly worms are not accurate predictors of winter weather. Many variables may contribute to changes in the caterpillar's coloration, including larval stage, food availability, temperature or moisture during development, age, and even species.

Woolly Worm Festivals

Although the woolly worm's ability to predict the winter weather is a myth, the woolly bear is revered by many. In the fall, many communities in the U.S. celebrate this cuddly caterpillar by hosting Woolly Worm Festivals, complete with caterpillar races. 

Where to go to race a woolly worm:

• Woolly Worm Festival - Held the 3rd weekend of October in Banner Elk, NC
• Woolly Worm Festival - Held in mid-October in Lewisburg, PA
• Woolly Worm Festival - Held in October in Beattyville, KY
• Woolly Worm Festival - Held in early October in Vermilion, OH
• Apple Festival - Held in late September in Central Square, NY (Woolly worm races are held as a fundraiser for the local search and rescue team.)