Why did the woolly bear cross the road?

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woolly bear on the road
Since roads don’t provide much cover for a caterpillar searching for seclusion, it is safe to say that woolly bears cross roads simply to get to the other side. (Tami Gingrich photo)

It never fails. When the month of October arrives, my driving becomes a bit erratic. As a lover of lepidoptera, it only makes sense that I would swerve left and right, occasionally crossing the center line in order to avoid flattening the barrage of woolly bears (Pyrrharctia Isabella) that have magically begun their autumnal movements.

Also known as woolly worms, woolly bears and autumn go hand in hand. As the leaves begin their colorful transformation from green into various shades of reds, yellows and purples, warmer days bring the addition of orange and black, as woolly bears make their appearance by the hundreds, parading across local roads.

Woolly bear look-alikes

woolly bear and giant leopard moth
There is another species of caterpillar that is often confused with the woolly bear, also out and about during this time. Large, black and bristly, the giant leopard moth caterpillar is at least a third larger than the woolly bear. (Tami Gingrich photo)

There is another species of caterpillar that is often confused with the woolly bear, also out and about during this time. Large, black and bristly, the giant leopard moth caterpillar (Hypercompe scribonia) is at least a third larger than the woolly bear. When touched, it curls into a tight ball for protection, divulging orangey-red bands of skin between the bristles. Curling up tight is a defense mechanism that both species deploy when disturbed. And speaking of bristles, neither species sports the type that typically causes an irritation to the skin.

Woolly bear lifecycle

Isabella Moth (mature woolly bear)
A woolly bear is actually the larvae of an Isabella tiger moth. (Tami Gingrich photo)

Most think of woolly bears as just that, a fuzzy caterpillar. But there is so much more to their lives, a complete metamorphosis, in fact.

A woolly bear is actually the larvae of an Isabella tiger moth. These moths, around 1.5 inches long, begin making their appearance in May and June at porch lights around the area. Having recently emerged from their cocoons, they are a lovely, pinkish-orange in color with an abdomen sporting a line of black spots. The moths are quick to mate and deposit their eggs.

Unlike some lepidopteran species that feed exclusively on just one or two species of host plant, the Isabella tiger moth isn’t picky. She lays her eggs on many species of trees and shrubs as well as on grasses and forbs. Having such a wide buffet ensures the success of a higher percentage of her offspring.

Upon hatching from their eggs, which are deposited in large groups, the tiny caterpillars feed together for the first few days before dispersing to forage on their own. Throughout the summer they eat and grow and are hardly ever seen. However, to come across a tiny woolly bear in its early development is pure cuteness.

By Autumn, the caterpillars have attained good size and around the time of the first frosts that inevitably kill their food sources, they begin their determined wanderings. You see, unlike other moth caterpillars which form a cocoon in the fall and overwinter to produce a moth the following spring, woolly bears follow a different agenda. Their autumn ambles are simply a search for a secluded spot in which the caterpillar can safely overwinter in its current stage until the spring.

During winter hibernation, woolly bears have been known to freeze solid with no ill effects. This is because their bodies produce a chemical anti-freeze which keeps their organs and body tissues from becoming damaged. Have you ever trudged out through the snow to grab an armload of firewood and found a woolly bear sleeping between the logs? In a case like this, moving it to a new sheltered location would be a great act of kindness!

With the onset of spring along with warmer temperatures, woolly bear caterpillars rouse from their sleep and begin to eat again. After a few weeks they seek out yet another sheltered spot. Here, they combine the bristly hairs that cover their bodies with fine silk to form a neat, fuzzy cocoon. In less than a month, their transformation into an adult moth is complete and the cycle begins again.

Predicting the weather

woolly bears
As woolly bears grow, their black hairs tend to be replaced by orange ones each time they molt, producing a host of mature caterpillars that give the nod to a gentle winter. (Tami Gingrich photo)

It is said that the woolly bear can predict the nature of the upcoming winter by its coloration. A caterpillar that displays more orange than black foretells of a mild winter with little snow and warmer temperatures. Larger bands of black indicate that a severe winter with frigid air and lots of snow is in the making.

Alas, this is simply a myth. Actually, as the caterpillar grows, the black hairs tend to be replaced by orange ones each time it molts, producing a host of mature caterpillars that give the nod to a gentle winter.

So why do woolly bears cross the road?

It would seem to us, because of the large numbers that we see, that the caterpillars are actually attracted to pavement. Rest assured, however, that the same numbers you see crossing roads are present crossing driveways, fields, pastures, lawns, the entire countryside! Since roads don’t provide much cover for a caterpillar searching for seclusion, I think it is safe to say that woolly bears cross roads simply to get to the other side.

Different color patterns of woolly bears
Woolly bears display a wide variety of color patterns during the fall, depending on their maturity. (Tami Gingrich photo)

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A life-long resident of Geauga County in northeast Ohio, Tami Gingrich recently retired from a 31-year career as a Biologist/Field Naturalist with Geauga Park District. Tami has been a licensed bird bander for over 30 years. Her hobbies include photography, lepidoptera, gardening and spending time with her husband on their small farm in Middlefield, Ohio. She welcomes any questions or comments at Royalwalnutmoth@gmail.com and will gladly consider suggestions for future articles.

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