Unique woolly bears head for shelter

During the fall in the Blackfoot Watershed, Isabella Tiger Moth and Spotted Tussock Moth caterpillars can be seen crawling in the sunshine across roads and over fences. These caterpillars are known as woolly bears. While some believe their coloring can predict the weather, other features of their life cycle push the boundaries of what some would think is science fiction.

Many moth species have fuzzy caterpillars that go by the name of woolly bear or woolly worm. Woolly bear caterpillars are the larvae of the brightly colored moths in the family Eribedae. They belong to the Tiger moth subfamily (tribe Arctiinae). Handling larvae is discouraged because their hairs may cause skin irritation.

Woolly bears' bodies are segmented in 13 sections with black ends and rusty red middles. The mature Spotted Tussock caterpillar has similarly colored bands with a variation of longer white hair tufts poking up. 'Tussock' means tufts.

The orange and black-banded woolly bears have a legend of being weather predictors. According to the Old Farmer's Almanac, the longer the rusty middle section the milder the winter. If the middle section is smaller the winter will be more severe.

However, entomologists said the width of the bands varies among the larval instar stages because of the weather. According to the Iowa State University Bug Guide, wetter weather can attribute to longer black bands. As the larvae mature the black bands get longer.

The bands can also vary in size from the health of the caterpillar. According to "Western Forest Insects" by R.L. Furiss and VM Carolin, the better the growing season, the bigger the caterpillar and the narrower the colored band in the middle. It is an indicator of the past growing seasons growth rather than an indicator of the severity of the upcoming winter.

The mythical stories have led to festivals celebrating the woolly bear including costume contests, foods and parades throughout the United States.

These caterpillars are also known for being cannibals. Some credit this as a plant adaptation. When some plants feel threatened by these caterpillars, they emit a defensive chemical that will protect them from pests and cause the pests to turn on each other.

Another characteristic some find intriguing is their ability to freeze and then come back to life.

Insect researcher Amanda Williams said that when the woolly bears prepare for winter hibernation, they look for leaf piles and loose bark on trees and logs. Their metabolism slows and they dehydrate for protection from the freezing temperatures.

The woolly bear circulatory system produces a cryoprotectant called glycerol which causes their tissues to freeze solid as winter conditions continue.

In the spring the caterpillars thaw out and search for food. Missoula County Extension Plant Specialist Sandy Perrin said the caterpillars mainly eat herbaceous plants including plantains, lupine, dandelions, grasses, birches and sunflowers.

Then they rip out their hairs to make a cocoon. Pupation occurs, and they do not eat at this time. Wings and antennae develop after one month and then the moths appear out of the hairy bristly cocoons. The moths don't eat either, but mate, lay eggs and then die. The eggs hatch in two weeks with the banded crawlers looking to eat.

More information can be found at https://bugguide.net/node/view/539