Wilderness Underfoot: The woolly bear

StoryImage( ‘/Images/Story//Auto-img-119015102016722.jpg’, ”, ‘Banded woolly bear caterpillar – with distinctive bands of black on either end of a reddish brown center, this is the most common of the various species we call woolly bears. It is the larva of the Isabella tiger moth, Pyrrharctia isabella (below). Woolly bears are found throughout most of North America, from Mexico to Canada.’);
StoryImage( ‘/Images/Story//Auto-img-119015103711080.jpg’, ”, ”);

Making its appearance at the end of summer, just when the populations of other insects are beginning to wane, the woolly bear is a remarkably hardy little creature. This late-season caterpillar emerges from its egg with just enough time to grow and fatten before starting its winter hibernation.

You may be familiar with the popular story that the size of this caterpillar’s black bands can help predict the severity of the upcoming winter. Unfortunately, that story is simply untrue. In fact, the size of the black bands varies widely among caterpillars even within the same brood, and the black area typically gets wider as the caterpillar ages. It can also be affected by moisture levels within the caterpillar’s environment.

Even so, the woolly bear caterpillar actually does have a fantastic talent regarding winter, of which most people are unaware: it can freeze solid and survive. Members of its genus can even survive in the chilling Arctic region, for periods as long as 10 months, frozen solid with no damage whatsoever! They can tolerate temperatures as low as -60 degrees Fahrenheit.

In the late fall, woolly bears will travel great distances in search of suitable hiding places for winter. This is why you often see them crossing roads and sidewalks. These resilient caterpillars can occasionally be found even in midwinter, during melts when sunlight warms the leaves and debris where they’ve been hibernating.

When spring arrives, the woolly bear will spin a cocoon and metamorphize into a pupa. Within a few weeks, it emerges from the cocoon as a moth (its adult form). The species we’re most familiar with turns into the Isabella tiger moth. Although these creatures may be found around your house and garden, neither the caterpillar nor moth are harmful. Woolly bears typically feed on wild plants, and not cultivated plants.

The Isabella tiger moth has yet another interesting trait: it uses sound to communicate. This moth has a little drum-like tymbal in its thorax (the middle segment where legs are attached). During courtship, females will produce clicks in response to males. Some species of tiger moths can actually use drumming signals to warn bats that they taste bad and should be avoided.

from the Sept. 19 – 25, 2007, issue

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