AUTUMN BRINGS NEW QUESTIONS

by Whit Gibbons


November 18, 2007


Autumn brings many changes, and ecological questions. The following are about a common caterpillar most people see at this time of year.

Q - What are these furry little bugs called woolly bears that I see crossing the highways in the fall? I've heard you can predict how cold the winter is going to be by the width of their bands.

A. Woolly bears are the caterpillars of the Isabella tiger moth, which is a yellowish moth with a wingspan of about two inches. The caterpillars attract more attention than the moths because they are indeed an insect we see as it crosses roads. They have fuzzy looking bristles that are arranged in three bands--a black one at each end and a brownish orange one in the center. The size of the bands varies among individuals, and one superstition is that the width of the middle band indicates whether it is going to be a cold or mild winter. I'm not sure which width is supposed to indicate a cold winter, but it does not matter since woolly bears are no better at giving long-range weather forecasts than the Farmer's Almanac or the National Weather Bureau. As far as the bristles go, woolly bears are completely harmless (except to the rare person who happens to be allergic to them) and can be picked up. In fact, I like picking up woolly bears because they roll into a neat little fluffy ball.

Q. - I know what a woolly bear caterpillar looks like, but what are they doing roaming around before it gets cold every autumn? Where are they going?

A. - When they are moving in the fall, they are probably looking for a place to bed down for the winter, or if it is still warm, looking for more plant material to eat. Caterpillars of some moth species turn into pupae and form cocoons before it gets cold, but woolly bears stay caterpillars all winter. Entomologists (scientists who study insects) have actually found that woolly bear caterpillars are able to withstand freezing temperature by producing a substance in their bodies that acts like antifreeze. When warm weather arrives in the spring, the caterpillars begin eating again and soon turn into pupae that form cocoons. In a couple to three weeks the moths emerge and are active in the summer. A question entomologists don't know the answer to is, how do woolly bears always know to cross perpendicular to the road, which is always the shortest distance to the other side?

Q. - Are these orange and black caterpillars I see on the highway nearly every fall one of the stinging kind I have heard of? They seem to be pretty bristly. Would it be safe to pick one up?

A. - A few moth caterpillars indeed have bristles that are hollow tubes containing venom that break off in the skin and can be very painful. At least one instance of a recorded death in the United States, a little girl in Florida, has been recorded from the sting of several saddleback caterpillars, a species which has such venomous spines. The Io moth has a pretty, greenish yellow caterpillar, with red and white stripes on the side, and the male turns into a large and beautiful yellow moth with huge circles on the wings that look like eyes. The female Io moth is brownish without the eyespots. Despite its elegant appearance the Io moth caterpillar is a stinging species. Most caterpillars that have ornamental spikes and spines that are very conspicuous are actually not venomous. But by appearing formidable they probably avoid being eaten by some predators that would like a tasty caterpillar meal. Woolly bears are bristly but they do not have the venomous kind.

Q. - What states are these so-called banded woolly bear caterpillars found in? I saw them in the fall when I lived in the Midwest and now have seen them after moving down South.

A. Woolly bear caterpillar larvae and their tiger moth adult stage are found in virtually all of the continental United States. They even range into Canada and Mexico.



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