Can Woolly Bears Really Predict Winter?

By Taylor on November 14, 2014 in Blog

Photo by Patrick Snell, Mark Ackelson Fellow

Many Iowans have probably heard of the Woolly Bear (Pyrrharctia isabella) or the Woolly Worm.

If not, folklore states that the Woolly Bear can forecast the upcoming winter by the colors on its fur. The Woolly Bear has 13 ridges that can be either black or brown. The 13 ridges are to help signify the 13 weeks of winter. The longer the black markings are on either end signify that there will be a harsher winter. You can also estimate if the beginning or the end of winter would be worse. If the black is longer on the head then it will be a harsher winter the first few weeks, if on the tail then the last few weeks.

But, this folklore is actually not accurate. The coloring of the caterpillar has multiple different factors, such as how long it has been feeding, its age and what type of species it is. Also, it has the fur to help protect themselves from the winter. It helps them create an anti-freeze around their body and they can survive to temperatures up to -90 degrees.

Before these caterpillars grow up to be Isabella Tiger Moths they spend 14 years as a caterpillar. They shed their fur six times before they become adults and they grow to about an inch and a half long.

Information courtesy of the National Weather Service.