Wooly Bears

Perhaps like you, I have been seeing lots of wooly bear caterpillars this fall. They are easily identified by their coat of long bristles or hair-like projections. The mid section of course is a reddish-brown, while black bristles cover the rest of the body. Wooly bears have given many kids their first introduction to entomology and the cycle of life. Remember those wooly bears kept in glass jars with holes punched in the lids? Many adults still seem to have a soft spot for these interesting little insects.

Wooly bears are the larval or caterpillar stage of tiger moths, and can be found over much of North America with the exception of the far north. They feed on a variety of herbaceous plants but seldom, if ever are pests. They emerge from eggs during the fall and of course are often observed before they crawl into the crevices of bark on trees, or find some other safe and snug place to spend the winter. They will produce an anti-freeze like substance in their bodies to keep them from freezing so that they can emerge safely next spring, pupate, and emerge as adult moths.

As many of you know, the width of the reddish-brown band of bristles on wooly bears can be quite variable. The variability is actually an indicator of the maturity of the caterpillar. However, the width of the band is also reported to predict the severity of the upcoming winter: The wider the band, the more mild the winter.

I suspect that most people assume that this is folklore from long ago. But according to the 1999 Old Farmer’s Almanac, it goes back to only 1948. Apparently Dr. C. H. Curran, curator of insects at the American Museum of Natural History in New York City, decided to have a little fun. He averaged the length of the reddish-brown segments and with the help or encouragement of a reporter from the New York Herald Tribune, used the length of the colored band to predict the severity of the upcoming winter. He continued his “study” for several years, and the accompanying press coverage catapulted wooly bears right up there with woodchucks for predicting the weather.

By the way, I have been careful to observe the width of the reddish-brown band on the wooly bears I have seen. Based on those careful observations, I have concluded that we are in for an interesting winter.

Chuck Lura

Natural North Dakota is supported by NDSU Central Grasslands Research Extension Center and Minot State University-Bottineau, and by the members of Prairie Public. Thanks to Sunny 101.9 in Bottineau for their recording services.