10/28/2026
Looking at this woolly bear caterpillar (Pyrrharctia isabella), you might think that the upcoming winter will be mild with the thick orange and thin black bands that this specimen sports. The truth behind these stripes is actually age! When a woolly bear, or Isabella tiger moth, first hatches from their egg they are completely black. As they molt, the hairs on their backs begin to turn orange.
The myth that Isabella tiger moth caterpillars predict the upcoming winter was given popularity by Canadian entomologist Dr. Charles Howard Curran during his time working in Bear Mountain, New York studying the chemical DDT. While at Bear Mountain, he catalogued the black and orange band sizes of 15 individual caterpillars and made a prediction that was later published in a news article for the New York Herald Tribune.
One of the remarkable skills of the woolly bear is their ability to overwinter as full-grown caterpillars. During autumn, they will be on the move to search for the perfect place to hunker down in, like under logs or curled up in the leaf litter of your yard. As temperatures lower, their metabolism slows down, and the hairs on their body trigger a process in which their bodies produce a type of glycerol "antifreeze" that insulates their bodies to protect the delicate tissues in their bodies during fluctuating temperatures. They can withstand temperatures as low as -90 degrees Fahrenheit with this process.
Every year in October, Banner Elk, North Carolina hosts a Woolly Worm Festival. Residents of Vermilion, Ohio host a Woolly Bear Festival, which was started by TV personality Dick Goddard.
Woolly bears have many other names: banded woollyworm, weatherworm, black-ended bear, hedgehog caterpillar. What do you call these fuzzy creatures? Leave a comment and let us know!
Caterpillar photo taken by Naturalist Breanna at Red Brook Metropark
Adult moth photo sourced from butterfliesandmoths.org/species/phyrrarctia-isabella