How 'bout Those Woolly Bears?

Gray's River Almanac, Number 4

by Robert Michael Pyle - Lecturer

            I'm sure everyone has noticed the many big shaggy caterpillars crossing the highway this month.  Folks often ask me about them: What are they, why are they crossing the road, and why are there so many this year?  What do they eat, where and when do they make their cocoons?  What do they turn into?  And do they really foretell the weather?  Children everywhere love how Woolly Bears gallumph across the road and curl up in your palm when you pick them up.  As Anna Botsford Comstock wrote in her Handbook of Nature Study (1911), "it seems to them a companion of the road and the sunshine; it usually seems in a hurry."  But where is it going?

            The animals in question are commonly known as Banded Woolly Bears, for their round, fuzzy, teddy-bear-like appearance.  The end segments, front and rear, are coal-black, while the middle portion is furred in fox-red bristles.  Their scientific name is Pyrrharctia isabella, and the adult animal is known in English as the Isabella Tiger Moth. If you will look carefully at the moths that come to your porch light on a warm summer evening, Isabella will be the ones that have smooth, oblong wings about two inches in wingspan, colored browny-yellowish or pale tangerine, with a few small black dots.  The hindwings, usually hidden, may be either deeper orange (the color of a Dreamsicle) or pale.  Females are lighter than the males, more straw-colored.  The body is bright orange with black spots down the middle.

            Female Isabella Moths may lay as many as 1,000 round little yellow eggs on a wide variety of plants.  Most butterflies and moths are quite specialized in their caterpillar host plants, but the young woolly bears are extreme generalists.  They will consume grasses, clover, plantain, dandelions, nettle, wild strawberry, maples, and many other plants.  They are not considered pests on any plants we care about in the garden, but they do have a very tolerant diet, which accounts for their common occurrence all over the country.  As they grow, they molt their furry skin several times, until they reach the size we usually see: an inch or two long, and as big around as a pencil wearing a fur coat.

            What Woolly Bears are doing when we see them on the roads is what lepidopterists call "going walkabout."  As Dr. W. J. Holland put it in his famous old Moth Book of 1903, the caterpillar "may often be seen by the roadside rapidly making its way in the fall of the year to a hiding-place in which to hibernate, or, in the spring, to some spot where they may find food."

It seems they have a strong attraction to roads, and in a sense, this is true.  Today I watched two of them jogging along Loop Road, not crossing it directly.  After all, the asphalt is smooth, offering no obstacles; and it is also heat-retentive, providing reflected warmth to cold-blooded insects on a cool day.  So the highway surface probably is attractive to them, often at the cost of their own lives.  However, it is a misimpression that they occur especially on roads; the fact is that they are wandering everywhere, and those that come to roadways naturally cross the roads; that is where we see them, because it is where we often go ourselves.  If we wandered around on our hands and knees in the general countryside, we would see them there too, crossing ant-trails and deer paths and rodent runs at least as often as human highways.  Skunks and possums find and eat them, rolling off the hairs first.  One neighbor's dog follows every Woolly Bear she sees on her road, never trying to eat them, but hopelessly beguiled.

            After their walkabout--and who knows how they decide how far is far enough?--the caterpillars hibernate under dry leaf litter, boards, or similar shelter.  When they come out of hibernation in the spring they feed for a while, then pupate.  Pupation consists of molting one last time from a caterpillar into a brown case called the pupa.  This chamber is wrapped in a tight cocoon that the caterpillar makes for itself out of silk and its own prolific hairs.  After ten days or so, during which the tissues of the caterpillar break down and reassemble as those of the adult, the Isabella Moth emerges.  In warmer climes there may be two generations of Woolly Bears per year, but here we have just one, usually flying in May, June, and sometimes into July, at night.  Once they mate, the females lay their eggs hither and thither to begin the new generation, which will become the next autumn's wanderers.

            Many of us are troubled by the inevitability of running over Woolly Bears in the road; I know I try to dodge them.  We won't hurt the population with our cars and trucks, but it's no fun running over wildlife--and these certainly are part of our wildlife, a handsome and much-beloved species at that, if small.  Still, it's not worth swerving too hard to avoid them.  As one friend of mine told me, after he dodged a caterpillar the other day below the east side of Salme Hill, his wife admonished him:  "You've got to look at the big picture!" By which she meant deer and elk.  It would indeed be a bummer to strike a large ungulate just to miss a caterpillar. 

            So how about the common folklore that says: if the Woolly Bears have thicker black bands of fur at the ends, the winter will be harsh, but if the middle, reddish part is broader, we'll have a light winter?  It's a lovely story, frequently told.  However, there doesn't seem to be any statistical support for it.  In fact, the band width is quite variable.  The black segments actually turn red as the larva grows and molts, which may mean that chilly, wet summers would see more slow-growing, heavily black-banded individuals; while hot summers would have redder larvae.  So the width and color of the fur muffs might have something to do with weather, but that would be a product of current conditions, rather than a predictor of the coming winter's severity.  The greater than usual numbers we are enjoying this autumn may be due to our extended Indian Summer, for these sunny, dry days are far more conducive to their walkabouts than sodden rain.

            What we do know is that these cute and fuzzy creatures always come out to greet us in the fall, adding a colorful and amusing element to the crisp fragrant days just before the frosts; and that country children everywhere love them.  They make great classroom animals, better than the commercial Painted Lady butterfly kits most schools buy for their second graders. Woolly Bears demonstrate the wonders of metamorphosis just as well, they are free, they hibernate happily in a shoebox full of dry leaves (kept outside, so as not to get too warm!), and they emerge as beautiful moths just before school lets out.

            As Holland concluded his account of the Isabella Tiger Moth, in the language of the times that assumed boys liked bugs more than girls: "Both the moth and the larva are common objects, with which every American schoolboy who has lived in the country is familiar; and unhappy is the boy who has not at some time or other in his life made the country his home.

'God made the country, man made the town.'"   Insert "schoolgirls" too, and all say, "Amen!"

http://smithsonianscience.org/wordpress/wp-content/uploads/2009/09/wollybear.jpg

http://www.moths.ca/arctiidae/pages/08129-pyrrharctia-isabella-A.html

Comments

[Thea Gavin]

I enjoyed reading this! Thanks Bob!