Woolly Bears on the Move

Although it’s fun to try to predict the severity of the coming winter by the amount of brown on a woolly bear caterpillar (the more brown = the milder the coming winter, according to folklore), the coloration of any given woolly bear caterpillar has more to do with its diet and age than the coming weather.  The more a Woolly Bear eats, the more frequently it molts, and each time it molts a portion of the black hairs (setae) is replaced by brown ones.  A Woolly Bear can molt up to six times — the best fed and oldest woolly bears, which have molted the most number of times, have the widest brown bands. (After overwintering as caterpillars, Woolly Bears pupate and emerge as small, brown moths called Isabella Tiger Moths, Pyrrharctia isabella.)