Fall Tidings of the Banded Woollybear Caterpillar

Written and illustrated by Mary Welz, Education Director

On a lovely afternoon in mid-October, I had a first fall sighting for the year of a banded woollybear caterpillar (Pyrrharctia isabella), during a visit to the future site of Sycamore’s Carl Ziegler Wetlands and Education Center north of Bloomington. Just as the leaves were beginning to glow with the vibrant hues of autumn, this intrepid individual was on the move, traveling upland from the wetland areas at the preserve, where it likely fed on such host plants as native asters or goldenrods. Larvae of this species are also known to feed on plantains, sunflowers, clovers, some grasses, as well as maple and elm trees. The iconic black and orange banded ‘furry’ caterpillar was unwavering in its journey, pausing only occasionally to investigate cracks and crevices along the way as potential hiding places to wait out the coming winter.

The larval form of the Isabella tiger moth, the banded woollybear caterpillar has long been associated with winter predictions. Folklore claims that the greater the amount of black on a banded woollybear, the more severe the winter weather. In actuality, research has revealed that the amount of black varies with the age of the caterpillar as well as the seasonal moisture levels during its development.

While science has debunked the myth of its weather forecasting abilities, the banded woollybear’s adaptation for winter survival offers further fascination.

To withstand the cold temperatures, the caterpillar finds shelter in leaf litter, under logs, or in rock crevices. It then undergoes unique changes in its body chemistry, producing antifreeze-like chemicals, known as ‘cryoprotectants’, to enter into quiescence, a term that describes a period of insect dormancy triggered by adverse environmental conditions which ends when favorable conditions return. Other charms of the banded woollybear include its characteristic habit of curling into a ball as a defensive mechanism when disturbed, much to the delight of anyone who has witnessed this behavior.

As a sign of the changing seasons, the banded woollybear caterpillar may rekindle our childhood wonder of nature and serve as a token of our continuing connection with the natural world.

Illustrations by Mary Welz: Banded Woollybear Caterpillar, Isabella Tiger Moth, Swamp Aster (larval host plant)

This article appeared in “The Shine Issue,” the Fall 2023 issue of The Twig, our membership magazine.