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?
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.
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.