THROUGH THE WOODS: Woolly bear caterpillars forecast winter weather?

Woolly bear caterpillar. Photo contributed

OUR TEMPERATURES ARE BEGINNING TO COOL OFF, and our little woolly bear caterpillars are starting their march across driveways, sidewalks and highways. They are off in search of a suitable crack or crevice to spend the winter months until warm weather allows them to complete their life cycle and reproduce. Their scientific name is Pyrrharctia isabella, also known as the Isabella tiger moth. In spring when the temperature gets to 40-50 degrees F, the caterpillar wakes up and spins a cocoon incorporating some of its own stiff hairs in the matrix. When the adult emerges in 2-3 weeks, it is a yellow/orange moth with a wingspan of about 2” and only lives 1-2 weeks.

In June, the moth finds a mate, lays eggs and dies soon after. The eggs hatch in 10-12 days to go into the larval stage. It is a small caterpillar at first and can hold on to a wisp of cocoon silk that it uses as a balloon for travel. It eats a variety of vegetation like clover, dandelions, maple leaves and grass, then goes through molts and increases in size to the 2” caterpillar we see in fall. It has 13 segments with the end segments usually black, and the center one a reddish brown.

When I was a little girl, I found a woolly bear, and my parents told me to be careful or it might bite. I was curious so picked it up anyway and found that unlike some other caterpillars, this kind did not bite. I was lucky. It did feel weird though, because of the stiff bristly hairs that touched the palm of my hand when it curled up in a tight ball and played dead. I carefully put it down and watched it slowly uncurl and go on its way.

My grandfather told me how they predicted the severity of the coming winter. I think I also read about this in an Old Farmer’s Almanac. It was always a family discussion on our farm as we found numbers of woolly bears and observed the size of the red central band in relation to the black end bands. If the red band is large it predicted a mild winter. By spring we usually forgot what the prediction had been so never knew how accurate it was.

During the winter, the woolly bear can withstand temperatures below -30 F, nearly freezing solid during winter hibernation. Their body produces a chemical called a cryoprotectant that acts like an anti-freeze which protects their organs and body tissues from being damaged. Once spring arrives and the outdoor temperatures begin to warm, the caterpillar thaws out and becomes active again. According to the Old Farmer’s Almanac online, there’s evidence “that the number of brown hairs has to do with the age of the caterpillar—in other words, how late it got going in the spring. The band does say something about a heavy winter or an early spring. The only thing is… it’s telling you about the previous year.”

I have started examining the caterpillars this fall, and so far, no prediction can be made. Check them out, and we will see. A mild winter would be nice.

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