Wooly Bear Caterpillars: Fact and Folklore

Wooly bear caterpillars are the familiar little fuzzy caterpillars with black ends and a russet-colored band around the middle. Their adult stage is Pyrrharctia isabella, the Isabella Tiger Moth. Other species of moths also have fuzzy bear caterpillars, including the light russet colored Spilosama virginica, or Yellow Bear, the all black Ecpantheria scribonia, or Giant Leopard Moth, and several colors and species of tussock moths. Some species may have glands connected to the tufts of setae, the little hairs on the caterpillars. These glands produce a stinging poison that is released when you touch the caterpillar. Note that Isabella wooly bears do not have any stinging ability, although their setae and their little feet do tickle.

Common russet-banded wooly bear caterpillars feed on many grasses and weeds throughout the summer. Dandelions, plantains and nettles are a few of their favorite broadleaf weeds. In the fall, after growing into mature larvae, wooly bears leave their food plants and move to areas where they can safely hibernate over the winter. Sometimes they can be seen moving en masse from a field to a wooded area. They seek out dark, sheltered places under leaves on the forest floor, near tree roots, in hollow logs, woodpiles, thickets or rocky crannies. They remain in the larval stage all winter long, curled up into a little fuzzy coil. You may inadvertently uncover a hibernating wooly bear in the winter, perhaps on firewood or under a tarp. Simply replace the dormant little caterpillar, or move it to another protected area without warming it up, and it will finish out the winter just fine. Wooly bears actually produce their own antifreeze, which permeates their cells and keeps them from freezing.

Warm spring temperatures bring wooly bears back to life, usually March through May. They may spend a short time feeding, and then they spin a brown cocoon. Pupation lasts for 2 to 3 weeks, when the adult Isabella Tiger Moths emerge to mate and lay eggs. Northern areas usually have two generations a year, and southern areas may have three or four generations, often overlapping.

FOLKLORE: The width of the russet band on a wooly bear caterpillar is an indicator of the severity of the upcoming winter. Narrow russet banding indicates a harsh winter, while a wide russet band means the winter will be mild.

FACT: The width of the russet band actually indicates the maturity of the caterpillar. A caterpillar that has been feeding for a long time and has grown larger due to a good food supply will have narrower russet banding with more black on the ends.

Click here and scroll down to the third photograph for some close-up images that show the spiracles on wooly bear caterpillars. Spiracles are the lateral respiratory stomata - all caterpillars have nine pairs of spiracles. You can see spiracles easily with your naked eye on wooly bears, but these pictures show you exactly what to look for.

Sources:
Personal Experience
Images: http://www.cirrusimage.com/woolly_Bear_Caterpillar.htm