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 

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

Links to Related Sites

Link to Iowa State University  Entomology Image Gallery
Old Farmers Almanac  The Truth about Woolly Bears
Article by Anita Carpenter  in the Wisconsin Department of Natural Resources magazine
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