Woolly Bears and Tiger Moths

Wooly Worm Festival

Woolly Worm Festival by Gideon Lichfield (Creative Commons BY-NC-SA licence)

What child is not intrigued by woolly bear caterpillars?  Our little granddaughter, Elanor, certainly is.  Last September she gathered up a handful of the bristly creatures as they paraded across our veranda and claimed them as pets.  I tried to discourage her, but she was adamant, and her father, Steve, who is an amateur entomologist in his spare time, humored her.

Later, I was relieved to learn that because woolly bear caterpillars are almost fully fed in the fall and will eat a wide variety of green plants that their pint-sized captors will feed them, they make good, short-term pets. 

But folks in Banner Elk, North Carolina, take woolly bear caterpillar pet-owning to a much higher level. They hold a two-day, Woolly Worm Festival the third weekend in October.  Although the festival has hundreds of food vendors and varied live entertainment, for 33 years it has focused on Woolly Worm Races.  Last October, 1,604 racing caterpillars and their young trainers competed, and nine-year-old Noah Jens’ pet, Wilbur, won the thousand dollar prize.

To compete, every woolly bear had to race up a three-foot length of string.  Since they move on average four feet a minute, the numerous races don’t last very long.  Once they declare a winner, after dozens of heats, they use the pattern and color of the woolly bear champion to forecast winter weather.  According to the woollyworm.com website, “the Woolly Bear caterpillar has 13 brown and black segments that correspond to the 13 weeks of winter.  The lighter brown a segment is, the milder that week of winter will be.  The darker a segment is, the colder and snowier the corresponding week will be.’

I don’t think I’ll accept that bit of folklore, because one woolly bear I saw last fall was almost entirely brown except for its black end, and we had a terrifically long and snowy winter.  Furthermore, scientists claim that woolly bear caterpillars have six or seven instars and the older they are the more brown hairs they have; hence, my woolly bear was merely an old one.

Still, I’m sure the Woolly Worm Festival, which had 20,000 attendees last fall, with its face-painting, dancing, and live bands, is a lot of fun and possibly the only festival in North America devoted to a caterpillar.

woolly bear caterpillar

wooly bear caterpillar by Tony the Misfit on Flickr (CC Attribution licence)

The woolly bear, also called the “black-ended bear,” “fuzzy-wuzzy,” “woolly worm,” and “banded woolly bear,” spends the winter under leaf litter and boards, although we have them curled up on our outside cellar stairs and on our heated basement floor.  Then, it pupates the following spring.  Eventually, it morphs into the orange-yellow Isabella tiger moth—Pyrrharctica Isabella—one of 11,000 members of the Arctiidae family worldwide.

Like many tiger moth caterpillars, they taste bad to predators so they don’t bother to hide during the day, but why they wander when they aren’t particular about their food, puzzles researchers.  In fact, many temperate arctiids, which include such species on our property as milkweed tussock moths (Euchaetes egle), fall webworms (Hyphantria cunea), unexpected cycnias (Cycnia inopinatus), dogbane tiger moths (Cycnia tenera), virgin tiger moths (Grammia virgo), giant leopard moths (Hypercompe scribonia), Clymene’s haploas (Haploa clymene), and banded tussock moths (Halysidota tessellaris)—are the only abundant, widespread, and species-rich lineage of Lepidoptera that crawl over bare ground during the day in North America.

Most are dietary generalists; fall webworms, for instance, eat over 400 plant species.  Yellow bears (Spilosoma virginica), which are common in gardens and yards of the eastern United States, like a host of low-growing plants as well as woody shrubs and trees.

Instead of defending themselves, many arctiid caterpillars fall to the ground if they are disturbed or, like woolly bears and giant leopard moths, curl up in a ball.  The gregarious fall webworms in their messy nests thrash their bodies from side to side in unison. 

Arctiid caterpillars also take part in “walkabouts” in the fall.  A small peak in hormones that makes them stop eating, empty their guts, and search for a good place to spend the winter triggers this behavior.  While most overwinter as half-grown caterpillars, some species, such as milkweed tussock moths, banded tussock moths, and fall webworms, overwinter as pupae.

Arctiids are unpalatable to predators because either they have inborn noxious chemicals or obtain noxious chemicals through the plants they eat. The acquired chemicals are pyrrolizidine alkaloids (PAs) from principally the snakeroots and ragworts or cardenolids or cardiac glycosides found in milkweeds and dogbanes, which affect the hearts of vertebrates. Unexpected cycnias, though, are dietary specialists and only eat butterfly weeds, a species of milkweed.

milkweed tussock moth caterpillar

milkweed tussock moth caterpillar by Bruce Bodjack (CC BY-NC-SA licence)

Arctiid caterpillars can also hear.  Researcher Raeleen Wilson, who worked with milkweed tussock caterpillars, discovered that their tufts of secondary setae (hair-like outgrowths from their bodies) are actually their ears and suspects it is true for other arctiid caterpillars as well. She suggests whimsically that we should hum at other species of caterpillars and see if they react. Probably, they are listening for the wing beats of parasitoid wasps so they can hide.  Fall webworms, for instance, are parasitized by more than 50 species of parasitic wasps and flies, creating what David L. Wagner in his Caterpillars of Eastern North America calls a “parasitoid hotel” in their nests. 

When arctiids metamorphize into moths, they have ears on the third and last segment of the thorax or body. Instead of flying in loops to avoid bats, they answer the bats ultrasonically.  Even headless dogbane tiger moths will continue to click in response to bats as long as three hours after their decapitation.  When moths ultrasound, bats break off their pursuit for one of three reasons, according to researchers.  In the case of the southwestern tiger moth species Grote’s Bertholdia (Bertholdia trigona) and probably other species, as well, they jam the sonar of their main predators—big brown bats.  For other tiger moths, the sounds startle the bat, giving the moths time to escape.  Still other moths use their ultrasound to warn bats that they are toxic so the bats will leave them alone.

But many species of arctiid moths, including the Isabella tiger moth, also use their ultrasonic buzzes for courtship.  The males of most species emit these sounds before releasing pheromones (odors that attract another member of the same species) to attract females, but Isabella tiger moths, along with ruby tiger moths (Phragmatobia fuliginosa), are unique because only the females produce their ultrasonic buzzes. Sound is particularly important to milkweed tussock moths and other species that courtship feed on cardenolide plants because they don’t produce pheromones and need sound to attract mates. 

But in most arctiid species, a female begins the courtship process by releasing a volatile pheromone from a gland near the tip of her abdomen.  This forms an odor plume that a male follows upwind to a female.  Such a pheromone release is known as “calling” and occurs at a certain time of day or night depending on the species.  To emit these pheromones, a female takes an elevated post with her wings in a V shape, turns her pheromone gland inside out and then rhythmically pumps out many droplets of pheromone once every few seconds and for several minutes at a time. Some of this scent enters the wind stream.  The Isabella tiger moth is particularly adept at this, emitting copious amounts of her pheromone which wafts her odor plume farther downwind than most moths.

A male tiger moth finds a calling female by flying upwind.  If he loses contact with her odor plume, he practices “casting behavior,” by zigzagging laterally across the wind line until he makes upwind progress towards the female.  Once he gets close, he emits ultrasonic clicks that she answers with her own clicks.

Isabella tiger moth

Isabella tiger moth (adult form of woolly bear) by Steve Jurvetson (CC Attribution licence)

Some arctiid males also have scent organs that they use during courtship to release pheromones. Apparently, they are advertising the fact that they have fed on PAs and can offer females a nuptial gift containing a defensive alkaloid that will protect them and when transferred to their eggs, their offspring.

As researchers work with more of these interesting species, they discover fascinating variation in their behavior patterns.  The dogbane tiger moth male emits a six-second sound at the same time as he releases a cloud of pheromone.  If he can’t produce one of these cues, a female flees.  A denizen of fields, powerline right-of-ways and other open habitats, one of these caterpillars that feed on dogbane will deposit 50 to 60 eggs on the underside of a dogbane leaf.

The virgin tiger moth plays possum when it is handled roughly.  It flips its wings over its thorax and curls its abdomen downward, conspicuously displaying its bright yellow-and-black coloration until danger is passed.

The great leopard moth engages in chemical warfare by exposing its orange-marked, metallic blue abdomen and secreting an acrid-smelling solution from glands located in the first segment below its head.  We see almost as many giant leopard moth caterpillars in the fall as we do the woolly bears. Large, black, and densely-covered with stiff bristles, they too eat a wide variety of plants including cherry, dandelion, oak, plantain, sunflower, violet and willow.  They also spend the winter as caterpillars under logs and bark.  Unfortunately, tachnid flies frequently parasitize them so they stay hidden in leaf litter or under loose bark during the day when the flies are abroad.  Folks often find them when they are raking up leaves or cleaning their yards, but we see them out late in the fall after the flies are gone.  The moth is large and white, its forewings and thorax boldly spotted with black, altogether a handsome moth.

Some years we have a plague of banded tussock moths—hairy, yellow-brown caterpillars with black and white lashes at either end of their bodies.  They feed on dozens of plants, including the black walnut trees encircling our front porch where we eat our dinner during the warm months. Since birds don’t like these distasteful caterpillars, they are conspicuous and sometimes invade our porch and table by the dozens, disgusting our visitors from the suburbs, but delighting their children and our grandchildren.

Still another hairy caterpillar our granddaughter croons over is the handsome black and white hickory tussock moth (Lophocampa caryae), which also likes black walnut trees, in addition to hickory, ash, elm, oak, willow, and American hornbeam.  They lay their eggs in large batches and during their early instars remain in clusters of 1000 or more caterpillars.  Sometimes they irrupt and cause local defoliation, but I’ve never noticed such damage here.

Trying to identify caterpillars and moths continues to be a challenge for me.  One that intrigued me turned out to be still another tiger moth called Clymene’s haploa.  With its wings closed, the brown marking on its cream-colored forewings makes an inverted cross.  Its bristly, black and orange caterpillar specializes in PA-rich plants especially joe-pye weed and snakeroot.  It overwinters as a caterpillar and pupates in early summer.

Moths of most species and their caterpillars remain understudied, probably because so many of them come out only at night and/or are small and incredibly numerous.  We have far more moths than butterflies.  Amateur moth buffs, even in eastern North America, can make new discoveries, especially if they are interested in behavior as well as identification.  But those of us who are not night owls are pleased to see and identify numerous day-flying moths and search for their caterpillars.  I’ve made only a start with tiger moths and woolly bears.

woolly bear and hickory tussock moth caterpillars

woolly bear and hickory tussock moth caterpillars by Seabrooke Leckie (CC BY-NC-SA licence)

Walking the Lines

“Good fences make good neighbors,” Robert Frost once wrote. So do good surveys.

After procrastinating for years, we bit the financial bullet and hired a surveyor to survey our square mile of mountain land. The surveyor was the same one who had surveyed a portion of our property years ago when we had bought some more acreage. He had also surveyed another bordering neighbor’s property so we figured he already had a head start on the job.

Finally, after months of work, both in the field and the courthouse, he had finished, and my husband Bruce and I were eager to walk the lines he had marked.

The 25th of September promised to be fine, according to the weather forecast, but it was a chill 44 degrees and misty when we started out at eight in the morning. Black-capped chickadees, black-throated green warblers, and tufted titmice sang, called, and foraged in the yard black walnut trees while a gray catbird scolded from the depths of the forsythia bushes where it had nested in early summer. Blue jays and eastern towhees called on Sapsucker Ridge and white-tailed deer played tag in First Field.

We crossed First Field–still bright with goldenrod–and stopped to examine fat, torpid bumblebees clinging to the flowers, waiting for the day’s promised warmth to rouse them. Halfway through Margaret’s Woods, we turned left on to the Steiner/Scott Trail, which we had named in honor of two men who had hunted on this section of the property most of their lives.

As we ascended Sapsucker Ridge, a cardinal “chipped” in alarm at us, an always merry-sounding Carolina wren called and sang, and eastern towhees continued their antiphonal calling. A tangle of Pennsylvania smartweed blanketed the trail while hay-scented ferns grew along the trail’s edge and spilled over the bank. Tempting bunches of grapes dangled from wild grapevines twining over black locust saplings.

Then we hit the dead zone of fall webworms. Entire trees and shrubs were swathed in shroud-like webs, the worst outbreak we had seen in many years.

Fall webworms are the offspring of small, white moths that overwinter as lacy, brown-colored cocoons in the soil. The moths emerge in May, mate, and the females then lay clusters of eggs on the undersides of tree leaves. Those eggs hatch into hairy, grayish caterpillars with shiny, reddish-brown heads, a series of double black dots on their backs and reddish-brown dots along their sides. They immediately crawl to the tip ends of tree branches where they spin their webs as self-protection while they eat the tree leaves.

The late June brood is barely noticeable because it does little damage, but every seven to ten years the late brood in August and September runs amok. The leaves, though, have almost completed their cycle and will soon drop, so fall webworms do minimal damage to trees. Although they will eat any deciduous tree leaves, they favor wild black cherry, black walnut, and domestic fruit trees on our mountain.

But when we reached the mountaintop and turned left on Big Tree Trail, we found that fall webworms had also denuded witch hazel trees as well as every cherry tree along the ridge. Despite what the experts say, our fall webworms have never eaten oak leaves, so we were able to stop and admire the 44-inch diameter red oak for which the trail is named.

Eventually, the trail met the first of the orange surveyor marks, and we were finally walking the line. Big Tree Trail went downslope toward First Field while we continued straight ahead on Sapsucker Ridge Trail through a forest dominated by large black cherry trees.

Noise from Interstate 99 and the railroad below was amplified by thick valley fog. Even voices drifted up from 1500 feet below. The promised warmth and sunshine never materialized. Instead, a cold fog billowed in from the south as we walked along the ridgetop.

Once, we stopped to look at “holey water,” as Peter Marchand called it in a recent Natural History article. This water found in tree holes sometimes contains “hidden reservoirs of biodiversity,” Marchand says, nurturing as many as 140 species of protozoa, flagellate algae, bacteria and aquatic larval invertebrates such as mosquitoes, moth flies, wood gnats, midges, punkies, marsh beetles and syrphid flies.

The best tree holes are those that occur where trees grow together at the base, such as the twin chestnut oak tree we looked at. It had grafted together to form a catchment basin called a pan at its juncture and was lined with seamless, waterproof bark tissue.

But tree holes also develop in a single tree if the bark is injured, such as in the black birch tree hole we discovered next. Fungi and bacteria enter the tree, creating a hole by decay that the tree walls off with callus tissue, again forming a cavity large enough to hold water. Still other single tree holes form when branches break off during wind and ice storms.

There are tree holes and then there are outstanding tree holes. The two we found had the necessary stem flow trails down the bark that channel rainwater into the holes, carrying nutrients from leaves and bark. Autumn leaf fall supplies the rest of the energy tree hole communities need to survive, but the amount of water and leaves must be carefully balanced. If there is too much organic matter, it lowers the number of species and density of populations because it soaks up too much water.

Even though I poked a stick into the organic soup of moldering leaves, it was difficult to tell whether our tree holes contained enough of the needed balance to provide a food chain from protozoans to marsh beetle larvae, the keystone species of tree holes. All I could see was a drowned fall webworm in the chestnut oak tree hole and a drowned green caterpillar in the black birch.

We left the tree holes near the Sapsucker Ridge Trail to follow the line, maneuvering over large, moss-covered rocks. Clumps of white birches growing on the ridgetop were already an autumn yellow and covered with seed cones. Early autumnal color–the brilliant orange, crimson, purple and gold of black gum–decked the forest understory.

As we walked, an almost steady stream of deer ran off. Chipmunks “chipped” and gray squirrels scolded. All were no doubt drawn by the acorns pelting down in the chilly breeze.

Finally, we reached the middle of the Second Thicket, the end of our line on Sapsucker Ridge, and turned left down the steep ridge, accompanied by the calls of American robins and blue jays. Slipping and sliding, we passed wild grapevines overhanging Hercules club trees and, since this area had been logged by a neighbor before our survey, abundant hay-scented ferns and Japanese barberry shrubs. What had once been a diverse thicket of trees and shrubs that provided shade for 100 jack-in-the-pulpits in the spring, was now an example of what happens when logging–instead of forestry–is practiced. Aliens like barberry invaded and no new trees germinated under the blanket of ferns. At least the dead snags provided places for wild grapes to hang from and the Hercules clubs bore clumps of berries for wildlife. Still, I remember what it once was and mourned its earlier, more vibrant life.

From there we made our way back to the Far Field thicket, only a small portion of which we own, and found a fresh deer scrape marked by a dangling grapevine. We continued through our section of the oak-dominated Far Field forest to Roseberry Hollow and climbed steeply down and up and finally on through a more recent, “take any tree that is worth taking” logging by another neighbor. Twenty-five years before, the landowner had had the mountaintop oak forest “thinned.” All trees 12 inches or more in diameter had been cut. Now what little had been left had been dragged off, leaving an understory of mountain laurel and huckleberry partially shaded by a few crooked oaks, two groves of spindly black birches that sprang up after the previous logging, a scattering of red maples, and the recently-sprouted black locust trees.

The two-year-old slash was still difficult to walk through so we followed the line by walking along our Laurel Ridge Trail and looking over at the blazes. We also took the time to find the old corner post our surveyor had found.

After we crossed the powerline right-of-way, leaving the devastated land behind, we followed our trail system–mostly an extension of Laurel Ridge Trail–another mile to the end of the mountain. This is also an oak-dominated forest with an understory of mountain laurel.

Along the trail we found a recently fallen tree ripped apart by a bear, and we continued to scatter deer like confetti. When we stopped to eat our lunch we heard a flock of keening cedar waxwings.

Near the end of Laurel Ridge, over the continual beeping of trucks from the valley limestone quarry, Bruce said, “Cup your ears. Hear the geese going over?” And indeed they were heading south that cool, overcast day.

In the grapevines just over the edge of the mountaintop, I sat down and watched a foraging flock of black-capped chickadees, eastern towhees, cedar waxwings, and one gray catbird. Best of all was an immature magnolia warbler that moved in and out of sight among the vines and tree branches.

We followed the line down the mountain a couple hundred feet before it became too steep. But we knew that the survey line dropped down to the railroad tracks and then followed around the end of the mountain to the interstate highway. From there it continued along the interstate fence until it cut straight back up Sapsucker Ridge to the top of the Steiner/Scott Trail where we had started our walk hours ago.

That steep mountainside area above the interstate has the biggest trees on the mountain but we never go into it. Aesthetically, it is unappealing because of the noise from the railroad and the interstate, but the wildlife seem to have no trouble with either aesthetics or challenging terrain.

So, instead of walking the rest of the line, we returned home by taking Black Gum Trail on Laurel Ridge, dropping down into the silence of the hollow, leaving behind the din from the town, the valley, and the nonstop traffic on the growing web of highways at the base of the mountain.

I found a couple of American chestnuts on the ground and traced them to a tree seven inches in diameter. The chestnuts’ spiny exteriors had been broken open and the nuts extracted, proof that at least some wild creatures knew how to harvest what had once been the most abundant fall crop for wildlife.

As we walked the final mile on this meandering trail through a mature, mixed-oak forest, it was brightened by the glow from within of the trees for which the trail was named. Red-bellied woodpeckers and blue jays called as they harvested acorns from the trees, while squirrels and chipmunks foraged on the ground.

By then I felt the strain of the more difficult than usual walk and collapsed for a short rest on my favorite double chestnut oak with a tree hole that had long ago dried up and now formed a perfect seat for me.

At last I dragged my weary bones home, after five and a half rugged miles, proud to have walked at least a portion of our line, exploring both familiar and unfamiliar ground. Our surveyor had closed the lines on our property, and, as we had expected, we had gained some land and lost some land. Now, when I walk the trails I have walked almost daily for over 30 years, I can be confident of our property lines.

In Robert Frost’s “Mending Wall,” it is his neighbor who insists on rebuilding the stone wall that marks their property line. So they agree one day to meet “to walk the line and set the wall between us as we go.” Frost thinks the line is obvious. So did we once. But we have to agree with the neighbor who wants a clear, definite line, who “says again, “Good fences make good neighbors.”