Can a caterpillar really predict whether Iowa will have a mild winter?

Across the state of Iowa—an expert at the Iowa State University Insect Zoo says there may actually be some science behind the folklore about how the thickness of a woolly bear’s caterpillar stripes can help predict the severity of the coming winter. Ginny Mitchell, coordinator of the zoo’s insect education program, says a fellow entomologist in New York studied the fuzzy creatures in the 1940s.

Black-and-brown caterpillars are now widespread in Iowa as they seek safe places to spend the winter. As the story goes, Mitchell says the thickness of the track’s center strip is key to weather forecasting.

There are also theories that if the caterpillar is crawling south when you find it, it is trying to escape the impending northern cold, and conversely, if it is moving north, a mild winter is ahead. At least two communities—Vermilion, Ohio, and Banner Elke, North Carolina—host fall festivals celebrating the woolly bear caterpillar’s supposed predictive abilities. A noteworthy fact: according to Mitchell, these furry creatures hibernate in the winter, and their bodies contain a kind of natural antifreeze.

There are reports of woolly bear caterpillars surviving temperatures up to 90 degrees below zero and even spending the entire winter frozen in an ice cube, only to emerge beautifully in the spring. Once temperatures rise for the season, it will create a cocoon and emerge in a few weeks as an Alexandra or Isabella tiger moth.