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What you need to know for 01/17/2018

Woolly bears not really able to predict severity of winter

Woolly bears not really able to predict severity of winter

Woolly bears are the larval forms of a group of moths known as tiger moths. Legend has it that they

Who can predict the severity of the coming winter? Well, according to legend, one of our local insects seems to know. I am speaking of the little brown-and-black nomads that can be seen crossing driveways and sidewalks at this time of year — the cute and cuddly woolly bears.

Everyone seems to agree that woolly bears can predict the weather, but no one really seems to know what they are telling us. The woolly bear’s red band appears to be the key, but does a wide red band indicate a mild winter or a harsh one?

The answer is neither. A quick consultation of my Peterson Field Guide to moths revealed the following passage: “Colors change as caterpillars molt to successive instars [developmental stages], becoming less black and more reddish as they age. Thus, differences in color merely reflect age differences among the caterpillars as they overwinter and are not a reliable indicator of the severity of the winter to come.”

Larvae of moths

Woolly bears are the larval forms of a group of moths known as tiger moths. The adults of most species are marked with bold black-and-white bands, but there are a few species that are far more reserved in their coloration. It just so happens that woolly bears are the larvae of the Isabella tiger moth, which is one of the species that is more subdued in its appearance.

While the coloration of the adults may differ, the one thing that all tiger moths have in common is the general appearance of their caterpillars — large, active and very hairy. These long hairs are no accident either. Anyone who has ever tried to pick up a woolly bear knows that they are amazingly difficult to get a grip on. This is a characteristic of the hairs, which protect the caterpillars from predation by birds and small mammals.

Additionally, the hairs provide the woolly bears some protection from sudden changes in temperature, which frequently occur at this time of year.

Winter homes

The woolly bears that you see rambling around the landscape in the fall are out looking for good places to spend the winter. Some may find their way into your woodpile while others hibernate under rocks or the loose bark of downed logs. Wherever they end up, woolly bears will spend the winter as caterpillars and then resume their feeding in the spring.

Once they have gone through six molts (or “instars” as I mentioned earlier) woolly bears start to pupate. To do this they spin a cocoon around themselves into which they incorporate most of the hairs from their bodies.

Two weeks later, the rather uninteresting-looking adults emerge.

Next generation

Once mated, the females go in search of good food plants upon which they will lay their eggs (usually in May). Such plants include asters, birches, clover, corn, elms, maples and sunflowers. Just five days after being laid, the tiny woolly bears hatch from their eggs and begin feeding. They may stay together for a while, but after a few instars they feed separately.

After many weeks of feeding, the woolly bears pupate, change into moths, lay eggs and die. The second generation, which appears in August, will not have time to grow to full size before winter, so they eat for as long as they can before finding a safe spot to hibernate.

Some woolly bears live out their entire lives without ever experiencing winter, while others have to halt their development until winter passes, but none that see a winter will know how long it will last.

Bill Danielson is a professional nature photographer and author living in Altamont. Contact him at

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