Sagebrush sheepmoth (Hemileuca hera)
WITH NO BREEZE TO STIR the air and no sign of rain for weeks, the August morning was heating up fast. As open bunchgrass began to crackle under the sun, the whole landscape seemed to slide into the protective arms of the nearest plant. One little sagebrush lizard, colored like its namesake’s leaves and flowers, positioned itself on an outside branch to catch some rays. A thrasher sailed in to touch a crown of rabbitbush, then departed without a sound. Beneath the crinkled leaves of a balsamroot, the bright red underwings of a captured grasshopper shone through the open curtain of an orb spider’s web.
Walking a fallen fenceline, I spied what appeared to be a small white shield shimmering in and out of focus near the top of an ancient sage. From a distance, I took it to be a picked vole carcass or a cricket shell—the remains of a meal pinned aloft by some efficient shrike. But as I drew closer I saw that it was a motionless insect. Black eyespots blinked from the center of each wing, and black half-diamonds along their margins pointed straight at the open orbs. It was a female sagebrush sheepmoth, newly emerged from her pupa beneath the ground. Life’s liquid had inflated her wings, and she had scrambled up the branches to assume her position on the very top sprig of the bush.
I stepped cautiously forward, but she did not fly. Fine golden-orange veins threaded across her black and white wings, precious metal and fruit combined. The eyespots of her forewings came into focus as calligraphic black Cs, while those on the hindwings dripped into the shapes of fancy sixes and nines. The moth’s lower body, patterned with alternating bands of gold and black, could have belonged to a fecund bumblebee, and she accentuated the similarity by slowly curling the tip of her abdomen like a bee intent on stinging. I brought my face nearer, until I could see how her shoulders were wrapped in a luxurious stole woven from furry scales of foxy sorrel. Rich auburn tones topped her pate and swept to the tips of her wiry antennae. Short combs grew off each antenna segment, and a few on the outside of the left one looked bent or damaged.
A puff of wind sprang up, and the moth adjusted her legs for a better grip on the sagebrush. No matter how closely I approached, she did not budge. She pulsed her abdomen again, and I guessed she was releasing a plume of pheromone to ride the breeze. Somewhere in the acres of sagebrush that surrounded her, flying males were waving their own leafy antennae, equipped with elaborately combed receptors sensitive enough to pick up a female’s perfume from miles away. Like flicking darts, they were careening across the top of the sagebrush in wild zigzags, neither slowing to rest nor dipping for nectar. A male will quarter the wind until he intersects a scent plume, then row against the current of the breeze as he gauges the pheromone’s concentration against the lay of the land. The closer he approaches to the source, the more directly into the wind he flies, homing in on the sole purpose of his adult life. He has only a few days to fulfill his mission, for adult sheepmoths have no mouth parts for eating, no way to refuel. The perched female usually accepts the first male that finds her; soon after her eggs are fertilized, she flies off in search of a suitable host plant. For the rest of her brief life, she circles the lower branches of a succession of sage bushes, laying rings of pearly sage-colored eggs.
Early last September, on a gray morning with a cold wind bearing down, I came upon one such female. She was lying stock still on the ground near the central trunk of a spreading sage, hemmed in by the forest of branches around her. Her powdery scales had flaked away so that she looked more like a piece of littered newspaper than a fine white shield. Sharp twigs or a pecking bird had tattered both hindwings, and her antennae were folded horizontally across her beady eyes. The spot high on her shoulders where burnished chestnut scales once flashed was now rubbed bare.
And yet the gold filigree veins trailing through her wings still glowed with life. As I watched, she began to move her forewings very slowly up and down. After some minutes the hindwings also began to quiver; the shivering spread at an almost imperceptible pace until her entire body shook like some early aircraft warming its engine for liftoff. Both antennae stretched out, buffeted by the wind, and the moth began to crawl. Her legs clutched a low branch and hoisted her body off the sand. She fell back, scrabbled to gain the branch again, then teetered out to its end. There she hopped clear of the entangling twigs and lifted off. Within seconds she was up and away, flying the same crazy zigzag as the males, seeking another gnarled trunk on which to set out one more ring of eggs while she still possessed the strength.
SHEEPMOTHS BELONG to the Saturniid family, giant silk moths revered for size, pattern, color, and startling eyespots. Growing up in the Carolinas, my sisters and I would sometimes find a silk moth clinging to the screen door on a humid summer’s eve, or dripping from a tree limb after a thunderstorm. We would run to fetch our mother, and she would stop whatever she was doing and follow us outside to shimmer in the visitor’s presence. But Mother was not content merely to admire the moth; she wanted no less than to possess it.
My job at this point was to grab a Mason jar from the kitchen while she fetched a cotton ball and her red can of spot remover. My sisters and I would watch wide-eyed as she primed the cotton with a quick tilt of the can, gave the ball a wave to evaporate any excess liquid, then dropped it into the jar. While I held the lid on tight to prevent any fumes from escaping, she would pluck the moth from its perch, expertly fold its wings together, and gently place the insect inside our killing jar. For a moment, her bony wrist would hover over the jar’s wide mouth, then she would slide her hand away so that I, as lid man, could close the moth inside.
Mother insisted that we wait for exactly her prescribed time, and I can still see the red pentangle of the minute hand on her fancy cocktail watch creep from one bold black line to the next. With each tick, a new kaleidoscopic pattern would emerge from the center of the watch’s face, golden triangles that grew to teardrops and held me mesmerized until the time was up. While the seconds crept past, she would peer into the jar, pointing to the royal purple line that traces the leading edge of a Luna moth’s wings, then compare their peculiar shade of pale green to the languid summer moon. If it happened to be a Cecropia moth, she would show us its dark chestnut pattern and explain how Cecrops sprang from the earth. On the night we peeled a Polyphemus moth from a big red oak, she branded the single eye of the giant Cyclops on my mind forever.
Living among the lush hardwoods of the South, we never dreamed that wild silk moths might also flit through the high deserts of the American West. It never occurred to us that such a creature might fly by day instead of night, or take its name from a humble grazing animal rather than from a resplendent god. But if we had been living in Walla Walla instead of Waxhaw, Mother would have known about such things. On the hottest of August afternoons, she would have called for pillowcase, coat hanger, and broom pole to fashion one of her special nets, then sent us trundling through the sagebrush forest in search of Hemileuca hera.
When we returned victorious, our sheepmoth would have provided Mother with more fodder for her mothology. She would have spelled out the genus name and reminded us that hemi meant half. Pressing her palms together, she would have showed us how the moth’s folded wings conjured exactly half of the special shield carried into battle by the Trojan soldier Leucaspis. She would have made us proud when Leucaspis used this badge so effectively that his companions dubbed him White Shield.
Leaping to the species name, she might have spun a yarn about the jealous Hera, who always knew when Zeus was up to mischief. The day she caught her husband with a snow-white heifer, Hera saw the maiden Io in its face, and demanded that the tosser of thunderbolts give her the cow. Zeus, of course, could not refuse. Hera the goddess tethered Io the heifer to a tree and called on Argus, her servant stippled with a hundred eyes, to guard the girl closely. To counter Hera’s move, Zeus coaxed quicksilver-tongued Hermes to distract Argus. Hermes told stories long and slow until Argus’s many eyes were nodding in and out of sleep, just like the blinking eyespots of a sheepmoth in flight.
No matter how carried away she got with her stories, Mother always stopped after precisely five minutes had ticked past on her watch. At her nod, I would carefully uncap the jar so she could touch the moth’s body and pronounce it dead. Then, ever so gently, we would pin the outstretched wings on a piece of cardboard wrapped with black velvet. Our goal was to preserve the essence of the creature before its delicate body stiffened and the brilliant colors lost their sheen, and we took great pains to make it look as though the moth had simply settled onto our board for a short rest, ready to lift off again with the fall of night. We mounted many moths before I realized we would never come close.
THOMAS NUTTALL FELL under the spell of the outdoors early in life in his native Yorkshire; in 1808, at the age of twenty-one, he gave up a printer’s apprenticeship and sailed to Philadelphia. There, with the encouragement of a vibrant scientific community, he concentrated on plant studies up and down the Eastern Seaboard. In 1811, aiming to botanize farther afield, he took advantage of an opportunity to accompany the Pacific Fur Company’s overland expedition up the Missouri River as far as the Mandan villages, in what is now North Dakota. As the troop made its way across the Great Plains, the greenhorn naturalist came into his own, collecting like a man possessed. Ground squirrels, birds, snakes and lizards, beetles, ammonite fossils, flashy minerals, and chunks of petrified wood steadily filled up boxes alongside his plant specimens. The French-Canadian boatmen made great sport of his habits, especially after they found that his gun was often plugged with dirt from being used as a digging stick or loaded with seeds to ensure their safekeeping. Thomas Nuttall chuckled at his own peculiarities and continued to revel in all things natural.
When he returned to the East Coast, he embarked on an intense quarter-century of research and teaching, producing a comprehensive manual of North American plant life and a similar project on the continent’s birds. Even though his publications became early standards in their respective fields, Nuttall always regretted that he had never made it to the Rocky Mountains. Then, at forty-eight years of age, he was offered a chance to visit the Northwest by his friend Nathaniel Wyeth, a Boston businessman who was leading a trading venture to the Columbia. Nuttall’s collecting instincts sprang back to life; he resigned his teaching post at Harvard and invited John Kirk Townsend, a Philadelphia physician and bird enthusiast half his age, to join the excursion.
Wyeth’s expedition embarked from Independence, Missouri, in the spring of 1834. The procession included furmen, the two naturalists, three Methodist missionaries, and a herd of cattle. One of the missionaries, noticing that Nuttall often hurried ahead of the crowd to collect plants before they were trampled by the livestock, wrote that the botanist’s “characteristic ardour in his favorite pursuit has not been lessened by the lapse of three and twenty years.” Long before they reached the Rockies, the naturalists had cast aside their extra clothing, shaving kits, and soap in order to make more room for specimens. The party crossed South Pass, then proceeded on to the Snake River. A few miles upstream from the mouth of the Portneuf River in what is now southeastern Idaho, Wyeth stopped to construct his Fort Hall trading post. The delay provided a chance for John Townsend to experience the thrill of running buffalo, but Nuttall, wary of Blackfeet raiders, stuck close to camp. During the three weeks it took to build the post, he snipped samples of various willows that grew along the riverbanks and watched western marsh wrens scurry among the rushes.
The Americans left Fort Hall on August 6, crossing the Snake to find themselves engulfed in a wide sandy plain scoured by hot winds and covered with “luxuriant sage bushes.” Their time at Fort Hall and their journey across the Snake River Plain coincided perfectly with the annual mating flights of two species of sheepmoths. One was a crisp black and white, while the other sported melon hues, which varied from Crenshaw to cantaloupe. Thomas Nuttall captured and pressed several individuals of both types, perhaps to demonstrate the range of their coloration and to give himself a better chance of getting home with an example of each. As with so many of the small flora and fauna the naturalists saw along their journey, these moths were not yet known to the halls of science. At that moment in time, the chances of their delicate wings making it from the far reaches of the Snake back to the classifying rooms of Philadelphia must have seemed frightfully slim.
After a difficult four-week journey over shattered basalt fields and sideways mountain ranges, Wyeth’s party reached the Columbia River at Fort Walla Walla and continued downstream on horseback to the Dalles. There they procured three canoes to float down to Fort Vancouver, but they had been on the water barely an hour when an afternoon gale swamped the boats. As they waited through the following day for the wind to die down, Townsend, whose bird skins had escaped damage, watched his colleague attend to his precious specimens.
Mr. N.’s large and beautiful collection of new and rare plants was considerably injured by the wetting it received; he has been constantly engaged since we landed yesterday, in opening and drying them. In this task he exhibits a degree of patience and perseverance which is truly astonishing; sitting on the ground, and steaming over the enormous fire, for hours together, drying the papers, and re-arranging the whole collection, specimen by specimen, while the great drops of perspiration roll unheeded from his brow.
The sheepmoths Mr. N. collected along the Snake River must have required some of his most tedious attention.
At Fort Vancouver, Nuttall and Townsend boxed their various collections and shipped them by boat around Cape Horn to Philadelphia. A year later, Nuttall followed the same route home. His vessel met rough weather trying to round the Horn and was twice beaten back into the open Pacific. On the third attempt a dense fog settled around the ship, confusing her course for days. The clouds finally lifted to reveal a familiar landmark that proved she had made the turn into the Atlantic. Seaman Richard Henry Dana, who had been a student of Nuttall at Harvard, never forgot either the drama of the moment or the reaction of his professor to the news: “Even Mr. Nuttall, the passenger, who had kept in his shell for nearly a month, and hardly been seen by anybody … came out like a butterfly, and was hopping round as bright as a bird.”
Nuttall sailed into Boston just as John James Audubon arrived in the city to sell subscriptions for the fourth volume of his monumental Birds of America. Audubon, who had never visited the West, was anxious to obtain study skins and background elements from those regions. He breakfasted with Nuttall and a few weeks later the two met again at the Academy of Natural Science in Philadelphia, where Nuttall was sorting through his barrels of treasure from the Columbia River. The collector supplied the artist with birds’ nests, specimens of western plants, and pressed insects. Audubon purchased duplicates of more than ninety bird skins sent back by Townsend and took this bounty south to the home of his friend John Bachman in Charleston, South Carolina, where he painted new figures for his opus. Among them was a composition depicting a pair each of Say’s phoebes and western kingbirds, two totem birds of the arid West. The phoebes are perched on a leafless branch, their bills pointed up to worry a buzzing fly. The two kingbirds, joined by a scissor-tailed flycatcher, focus their attention on a pair of moths.
The patterns of these two moths are almost identical. Single eyespots, slightly crinkled, stare from the forewings of each insect; both heads sprout orange hairs; both abdomens are graced with similar dark and light bands. Only the colors of their wings are different: Audubon painted one moth’s wings a creamy white, while he dabbed the other’s with the pink of the phoebe’s belly in front and the yellow of the kingbird along its trailing edges. These are Thomas Nuttall’s Snake River sheepmoths, appearing in the public eye for the first time. But while the birds’ bodies carry the animation of life, the moths look as if they were hammered flat on the canvas. Audubon, painting from pressed carcasses two years old and two thousand miles removed from their home, had no more hope of capturing the living magic of those Saturniid moths than my mother and I did when we pulled them, oily and stiff with spot remover, from our killing jar.
His portraits completed, Audubon left the two crusty moths in Charleston with Bachman, who sent them to a friend in England, who decided they must be the male and female of a new species, which he assigned to the goddess Hera. Meanwhile, back in Philadelphia, Nuttall had presented several more sheepmoth specimens to the painter and naturalist Titian Ramsay Peale, who made etchings of a pair for his proposed Lepidoptera Americana and named them in honor of their collector. Eventually the moths were recognized as separate species, and the taxonomical confusion was resolved; the black and white moth retains the name of Hera, while the melon-colored one honors Professor Nuttall. The desiccated remains of both sheepmoths remain forever pinned onto Plate 359 of Audubon’s Birds of America, with those western kingbirds eying them as if they might make one last meal.
SINCE MOTHS HAVE no hard parts, their fossil history is very sketchy, but some lepidopterists believe the ancestors of western sheepmoths may have fluttered across the Bering land bridge at the very beginning of the last great Ice Age, more than a million years ago. Pollen counts from ancient lake bottoms reveal that most of the dryland shrubs we now associate with the intermountain West have been around since that time, following the ebb and flow of glacial movement. Insects of all sorts would have lived in concert with sagebrush and related shrubs like antelope bitterbrush, saltbush, and greasewood. Sheepmoths would have been a part of this scene, coevolving with the plants; over time different species developed to mirror the subtle diversity of their environment. Hera’s variety settled on big or tall sagebrush as its primary food plant, while Nuttall’s came to depend on the sprigs of antelope bitterbrush. In the millennia when these shrubs blanketed the arid West, both moths would have thrived, and it is easy to imagine clouds of white and melon-colored males roving across the steppe in search of females on clear, windless, late summer days.
The years since the sweep of Thomas Nuttall’s net have brought great changes to the sagebrush country. Grazing livestock, invasive weeds, large-scale agriculture, a complete shift in the pattern of water transport, and human sprawl have flooded through continuous stands of sage and bitterbrush. In the face of such alterations, sheepmoths have retreated to islands of healthy shrub-steppe that hearken back to what must have been a fluttering heyday for Hemileuca.
Professor Nuttall left behind no field description of sheepmoth males performing their aerial displays, or expectant females blossoming on the tops of their food plants. Most of the other early travelers to the sagebrush plains of the Snake and Columbia Rivers were so anxious to reach the verdant coast that they paid little attention to flying insects. While tribes of the southern Great Basin were keenly aware of the life cycle of such moths—figures on Miembres pottery depict spiny-backed caterpillars, and Paiutes around Mono Lake trapped the grubs of a close sheepmoth relative in pits, then roasted their bristles off in sand and dried them for use in winter soups and stews—Plateau peoples seem to have no stories or words directly connected to the sheepmoths. Perhaps it was because the abundant fish in this region provided bigger packages of more easily obtainable protein. Perhaps as the moths decreased in number, they simply faded from memory. But just because sheepmoths cruise beneath the reach of human radar doesn’t mean that some aren’t still out there, making their rounds.
In early spring, as the fresh new leaves of dryland shrubs begin to burst forth, the tiny egg clumps laid by female sheepmoths the previous summer finally hatch, and the larvae congregate into fuzzy black lumps on the branches of their natal bush. Close inspection of one of these writhing clumps reveals a knot of dark caterpillars pulsating with the rhythm of a single organism. Individuals crane their heads out of the pack, wave their six thoracic legs, then disappear back into the clump as others rise around them. This gregarious behavior allows the larvae to absorb more solar energy during the day and to keep warm on cool nights; it may also be a defense posture meant to startle preying birds and fend off insects. Amidst all the twisting and turning, the dozens of larvae inside the bundle are busy chewing away on tender leaves, fueling a growth spurt that will carry them through a succession of developmental stages called instars.
Over the next few weeks, the larvae increase remarkably in size, and the clumps separate into single caterpillars that pull their way along branches on five pairs of knobby prolegs. With supple strength they balance on their hind ends while twisting and flexing in acrobatic displays. By the time it reaches its fourth instar, a sheepmoth caterpillar is about the size of a baby’s finger, with yellowish seams running the length of its midnight body. Whorls of stiff yellow bristles, like tiny shaving brushes, sprout in tidy rows along its back and sides. These little spines contain a stinging chemical that can raise welts in the mouths of grazing livestock or on the sensitive skin of curious humans. Despite such defenses, their mortality rate is high; many larvae fall to hawking birds or play host to the eggs of parasitic flies and wasps.
As spring’s freshness dries to summer’s heat, the surviving caterpillars give up their voracious habits and slither down their bush to touch the earth. Like dogs settling for a nap, they circle the base or wander to adjacent bushes before slowing to a halt. Their bodies undulating from head to tail, they burrow into the thin desert soil. Then, instead of spinning cocoons like most of their silk moth kin, they exude a liquid gel that hardens into a glassy capsule. At first the new pupae glow like self-made amber, but air and time soon darken them to a glossy black.
Inside these fragile chambers, the caterpillars undergo a profound transfiguration. The larval mouths disappear, and complex eyes pop to the surface of the head. Segmented antennae develop, and dormant cells form four fragile, amorphous membranes that will one day become wings.
When the transformation is almost complete, subtle forces determine the timing of release. In the Columbia Basin, where warm weather lingers, most receive the signal to emerge at the end of summer, and so spend only one season underground. The biological clocks of others may keep ticking through an entire year, or even two, so that some sheepmoths do not emerge as adults until twenty-seven months after their descent. Only then do they wrench free from their chrysalises and dig upward through the soil. In the open, they pump elixir through the network of veins that gives shape to their new appendages, then begin the long climb to the top of their mother sage, where they spread their wings to match Leucaspis’s fine white shield.