Woolly bear caterpillars (Pyrrharctia isabella) are the larval stage of Isabella tiger moths. Found in most parts of the United States, Canada and Mexico, these caterpillars grow an average of 2 inches long. Their bodies are fuzzy with brown and black bristles, with black bands on each end and a brown band in the middle. Like many critters, woolly bear caterpillars hibernate over the winter.
After hatching from their eggs in the spring, woolly bear caterpillars spend their time eating. They forage on weeds such as dandelions, grasses and the leaves of trees like maples and birches. These critters prefer dry to somewhat damp habitats such as weedy fields, grassy backyards, roadsides, meadows and the edges of woodlands. As fall approaches and temperatures begin to fall, woolly bear caterpillars appear all over in great numbers. They travel in search of a safe place to settle down for the winter.
Woolly bear caterpillars look for a safe place to hibernate, in places such as leaf piles and under logs. As temperatures continue to fall, the woolly bear caterpillar's metabolism begins to slow down. The caterpillars are now ready for hibernation. For protection from the freezing temperatures, the caterpillars dehydrate themselves and their circulatory system produces a cryoprotectant, which freezes the tissues solid and prevents any water from freezing in their body. So long as winter conditions continue, the caterpillars hibernate and stay frozen like this.
Rest and Digest
As temperatures increase in the spring, woolly bear caterpillars begin to thaw out. They awaken and begin to prepare for becoming adult Isabella tiger moths. These fuzzy caterpillars spend a few nights eating plant matter, then prepare a cocoon. Their cocoons are crafted from their own black and brown bristles. Once fully in their fuzzy cocoon, the caterpillars pupate. They do not eat in this stage. Instead, they develop adult parts such as wings and antennae.
Rise and Shine
After pupating for one month, the now-moths emerge. The moths are tan or orange in color with fuzzy heads and several small black markings on their wings. Like pupae, the adult Isabella tiger moths do not feed. They spend only a few days mating and laying eggs before they die. New eggs hatch within two weeks and the cycle of life begins again.
- Ohio Department of Natural Resources: The Wonderful Woolly Bear Caterpillar
- USA National Phenology Network: Pyrrharctia Isabella
- 21st Century Parks, Inc.: Where Are You Going Wooly Bear?
- University of Wisconsin - Stevens Point: Woolly Bear Caterpillars Abound
- Washington State University: Woolly Bears
- Western Washington University: Isabella Tiger Moth
- The New York Times: Woolly Bears
- Thinkstock/Stockbyte/Getty Images