What the Wooly Bears Say About the Winter Ahead

Pyrrharctia isabella, the Isabella tiger moth, whose larval (caterpillar) form is called the banded woolly bear, woolly bear, or woolly worm, occurs in the United States and southern Canada. It was first formally named by James Edward Smith in 1797.

mature eggs

This species is a generalist feeder, consuming many plant species, including herbs and trees. Based on the caterpillars' wide range of food plants, this moth could be found almost anywhere that plants grow

Canadian and U.S. folklore holds that the relative amounts of brown and black hair on a larva indicate the severity of the coming winter. It is believed that if a Pyrrharctia isabella's brown band is wide, winter weather will be mild, and if the brown band is narrow, the winter will be severe. In a variation of this story, the color of stripes predicts the winter weather, with darker stripes indicating a harsher winter. 

Another version of this belief is that the direction in which a Pyrrharctia isabella crawls indicates the winter weather, with the caterpillar crawling south to escape colder weather. 

Next year, the caterpillars that survive winter will become Isabella Tiger Moths.

There is no scientific evidence for winter weather prediction by Pyrrharctia Isabella, but that hasn't stopped many places across the country from having wooly bear festivals. And it hasn't stopped many people - including myself - from taking note of these fuzzy critters and noting what they are "predicting" for winter. Actually, hatchlings from the same clutch of eggs can display considerable variation in their color banding, and a larva's brown band tends to widen with age as it molts.

Curious about our coming NJ winter?
Here is my own wooly bear's prediction for my part of NJ this winter.