Mixed messaging: Woolly bear molting confuses these caterpillars’ ‘forecast’

A woolly bear caterpillar with a wide section of rusty brown coat is one that has molted multiple times. An all-black woolly bear is one that has not yet molted. They are black when first hatched. The Isabella tiger moth is the adult form of insect into which a woolly bear eventually will grow.

Woolly bears really don’t know what the winter has in store for us.

These woolly bears of which I speak are not huge, shaggy predators that feast on salmon and backpackers. Instead, they are caterpillars — you know, those fluffy woolly worms of about 1 ½-inch long. More exactly, a woolly bear is the larval form of Pyrrharctia Isabella, the Isabella tiger moth.

We do not see much of the Isabella tiger moth, which is a pale yellow, lightly black-spotted insect that flies about during summer nights all across North America. We do see more of its offspring, the woolly bears that are on the move at ground level in daylight during the autumn.

Woolly bear skin sprouts a layer of bristling hairs that are properly called setae that provide them a little protection from such predators as birds. These semi-rigid bristles are what gives the woolly bear its fuzzy-wuzzy character, keeping it from looking like the wormy creature it is at this stage.

The colors of the caterpillar’s bristle coat give it looks that are both familiar to us and serve as the basis of a long-time folklore tale.

A woolly bear can be all black or it can be black on both the head and rump ends with a middle band of variable width that is an attractive rusty, orangey brown. The black/brown/black variety is probably the one with which people are more familiar.

The rusty-banded caterpillar apparently way back in some historical time gave rise to the claim that the severity of the coming winter is foretold in the colors of the worm’s bristling coat. Supposedly, a wide band of rusty brown on the woolly bears of the season meant that the winter ahead would be milder and more pleasant.

Conversely, woolly bears with a narrow brownish band and wider margins of black on the opposite ends would signal a harder winter with colder temperatures, snow and ice was in the making. And if all-black woolly bears started to show up, bar the door, we would likely be in for a really frigid ordeal during the wintry months to come.

Folklore was never particularly good at explaining how it is that woolly bears ranging from all black to mostly the orangey brown could and would all show up during the same fall. And none of the folksy old sages have ever excelled in explaining what that meant for the winter forecast.

Actually, it means nothing in the interest of forecasting.

Entomologists, the scientific bug gurus, will grant that there are some individual differences from one woolly bear to another. Sort of like people, within the same species, if you’ve seen one, you haven’t exactly seen ‘em all. There are variances.

But more importantly — and this is the one that toasts the folklore bit — all woolly bears are completely black when they first hatch from a fertilized egg and grow into a caterpillar.

Yet, they do not stay that way. Each woolly bear goes through a series of molts, each time when the caterpillar sheds its skin to facilitate growth and re-sprouts its bristling coat. And, get this, each time the woolly worm grows a new coat, the bristling setae sprout with an increasing amount of the rusty brown color.

The woolly bear typically molts six times, achieving a narrow band of brown on the first molt. Each time it molts over the summer-centered growing season, that rusty center section comes back a little wider until, with many, just the head and butt tips are black by the onset of cold weather of late fall.

What that means from scientific understanding is that all-black woolly bears are just the youngest, having not year molted. Those with some and increasingly wider margins of rusty bristles are a bit older, at least having molted more times.

What is happening that makes the caterpillars more visible now is that they are abandoning their favorite feeding areas in green grassy and leafy areas and looking for some sort of dark, sheltered area in which to do a caterpillar version of hibernation.

The woolly bear is not too concerned about the severity of the winter ahead because it really does not expect to escape the cold. Shelter is a relative thing to a woolly bear because it is made to endure winter’s punch and keep on ticking.

This tiger moth larva actually goes with the flow and freezes when temperatures grow severe. However, there is an inner part to its cells that is protected by a natural antifreeze. Most of the woolly worm can yield to ice crystals, but its cells at the center will resist freezing, when the spring thaw comes around, they bring the insect back to life.

I doubt if many people really believe that a caterpillar has any correlation with the severity of the winter ahead. For those who might put credence in woolly bear coats as prognostication, there is apt to be confusion when the full range of woolly worm colors appear each fall.

Best advice is to be prepared for a brutal winter whether or not you have seen at least one young, un-molted, all-black woolly bear. And if and when the winter proves milder — as what one of the brown-banded caterpillars might suggest — you can be pleasantly surprised.

Preparing for the worst and hoping for better is always a sound strategy. Don’t trust a woolly bear.

Steve Vantreese, a freelance outdoors writer, can be contacted at outdoors@paducahsun.com.

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