Forest Preserve District of Cook County, Illinois
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The Woolly Bear
Nature Bulletin No. 314-A   September 28, 1968
Forest Preserve District of Cook County
Richard O. Ogilvie, President
Roland F. Eisenbeis, Supt. of Conservation

Many children get their first glimpses into the fascinating world of natural history from watching the Woolly Bear Caterpillar -- the one with the dense even coat of "fur" which is rich red-brown in the middle and black on both ends. This is the larva of the Isabella tiger- moth and occurs in great numbers from coast to coast. It is commonly seen on sunny autumn days and always seems to be in a hurry, scurrying across roads, sidewalks and bare places in search of some safe place to hide before winter. When disturbed or picked up, it curls into a tight bristly ball and "plays dead". That is why it is called the Hedgehog Caterpillar.

There are 13 segments in its body, not counting the polished black head, but the rear two are so joined that they look like one. On each of the first three is a pair of true legs with little shiny claws. The next four segments each have a pair of false legs, called "prolegs", which are merely fleshy extensions of the sides of the body, and at the rear end is a "prop leg". Because it cannot see far with its tiny eyes, you may observe one clinging to a leaf while the front end rears up and feels in all directions for another place to go.

The segments are thickly studded with little wart-like tubercles, each of which bears a tuft of coarse stiff hairs. There is a superstition that if the middle band is narrower than either of the black bands on front and rear, then the coming winter will be severe; if the three are about equal it will be average; and if the red-brown band is widest, the winter will be mild. Almost invariably, the first three or more segments are black but occasionally all the rest are reddish. Most scientists agree, however, that this caterpillar is not a weather prophet; that the relative amounts of red and black are due to conditions of temperature, and perhaps moisture, during its early life. Experiments with some other insects, such as fruit flies and cabbage butterflies, show that their markings vary according to the temperatures at which they are raised.

The woolly bear, unlike many caterpillars, feeds on a wide variety of plants such as grass, clover, plantain, dandelion, spinach and cabbage. There are two broods: one in June or July, and another in September. The latter are the ones we see in autumn on their way to protected places under boards, logs, boulders, or in crevices, where they curl up and hibernate. In early spring they come out, feed for a short while, and then each spins an oval cocoon of silk interwoven and padded with its own hairs. The first adult moths emerge in late May. They are night fliers with three rows of six black dots on the abdomen and a wingspread of almost two inches -- tawny yellow wings with a few dark spots; the hind wings sometimes tinted with dull orange.

There are many, many species of tiger-moths, all with stout spotted bodies, but they vary greatly in wing colors and markings. Most of our other common hairy caterpillars are also in this family but pass the winter in the pupa stage instead of hibernating as caterpillars. Among them are the Fall Webworms, the gay Harlequin Caterpillars that usually feed on milkweeds, the Salt Marsh Caterpillar which is abundant over most of North America as well as in salt marshes, and the Yellow Bear. The latter has a dense uneven coat of long hairs which may be pale yellow, whitish or reddish. Altho it feeds on many kinds of plants it is frequently found in our flower gardens and greenhouses.

The Indians had the answer to caterpillars. They ate 'em.

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