How early settlers unwittingly drove their nemesis extinct, and what it means for us today
Picture swirling snow as far as the eye can see — in the middle of summer. Now, imagine this blizzard of flakes transforming into a swarm of locusts. This isn’t just any swarm, but the largest congregation of animal life that the human race has ever known. Picture yourself in Plattsmouth, Neb., in the summer of 1875.
A swarm of Rocky Mountain locusts streams overhead for five days, creating a living eclipse of the sun. It is a superorganism composed of 10 billion individuals, devouring as much vegetation as a massive herd of bison — a metabolic wildfire that races across the Great Plains. Before the year is up, a vast region of pioneer agriculture will be decimated and U.S. troops will be mobilized to distribute food, blankets and clothing to devastated farm families.
I came across an account of this staggering swarm in the Second Report of the U.S. Entomological Commission, published in 1880. By clocking the insects’ speed as they streamed overhead, and by telegraphing to surrounding towns, Dr. A.L. Child of the U.S. Signal Corps estimated that the swarm was 1,800 miles long and at least 110 miles wide. This suffocating mass of insects was almost large enough to cover the entire states of Wyoming and Colorado.
Swarms like this — albeit usually on a smaller scale — are part of the life cycle of locusts around the world. At low population densities, these insects behave like typical grasshoppers, to which they are closely related. But when crowded, this insectan Dr. Jekyll transforms into Mr. Hyde. Chemical cues from their feces and frequent disturbance of tiny hairs on their hind legs set off the changes. The changelings aggregate in unruly mobs, feed in preference to mating, grow longer wings and a darkened body, and irrupt into rapacious swarms.
It is as if whenever humans found that our neighborhoods smelled like sewers, and that we were constantly jostled on the way to work, we abruptly changed into throngs of anxious, red-faced neurotics with an inexplicable desire to buy a plane ticket or rent a U-Haul. Perhaps locusts and humans have more in common than we suppose.
This metamorphosis is probably a survival mechanism. In temperate ecosystems, locusts outbreak when droughts cause their verdant habitats to shrink, forcing the insects into crowded masses and signaling that it’s time to escape impending disaster. The swarms are like the Mongol hordes that once swept across the steppes in search of new lands. The immense clouds of Rocky Mountain locusts are the subject of frontier legend. Laura Ingalls Wilder’s On the Banks of Plum Creek revolves around the devastation wreaked by a locust swarm that descended on her family’s land:
"The cloud was hailing grasshoppers. The cloud was grasshoppers. Their bodies hid the sun and made darkness. Their thin, large wings gleamed and glittered. The rasping whirring of their wings filled the whole air and they hit the ground and the house with the noise of a hailstorm. "Laura tried to beat them off. Their claws clung to her skin and her dress. They looked at her with bulging eyes, turning their heads this way and that … Grasshoppers covered the ground, there was not one bare bit to step on. Laura had to step on grasshoppers and they smashed squirming and slimy under her feet …
" ‘The wheat!’ Pa shouted."
Today, this is hard to imagine; it sounds like an old Alfred Hitchcock thriller. But if we find it difficult to envision such masses of life, it is even more challenging to grasp that within 30 years of Dr. Child’s account of the largest insect swarm ever recorded anywhere, this species disappeared — forever. The last living specimen of the Rocky Mountain locust was collected in 1902 on the Canadian prairie.
But if we pay careful attention, the Rocky Mountain locust has lessons to teach us about abundance and extinction and our tendency, as a species, to stumble like bulls through nature’s china shop. Perhaps most importantly, the locust has troubling implications for contemporary society, and warnings about our future in a fast-changing landscape.
In 1986, I was hired as an insect ecologist at the University of Wyoming to explore the world of grasshoppers — a mission I’ve undertaken for the past 17 years. No sane person would devote so much time to pursuing a subject that did not touch the heart and soul while stimulating the mind. And I’ve found that grasshoppers hold mysteries and lessons that are worthy of this labor of love.
The science of entomology is an arcane discipline, and the story of the locust was peripheral even there. But the story had floated about for many years, and fascinated me because of what was missing as much as what it contained.
Soon after arriving at the university, I learned that the accepted explanation for the locust’s demise was a vague conspiracy of vast ecological changes. Entomologists proposed that the disappearance of bison, the decline of fires set by Indians, and changes in climate had altered the locust’s prairie habitats. But when I started digging through the evidence, none of these factors provided a satisfactory explanation.
The mystery was so intriguing, and the existing explanations so full of holes, that I was compelled to reopen the case. Besides, I had a lead on a bounty of clues that had scarcely been touched. Digging through old, obscure geological reports, I learned about the existence of "grasshopper glaciers," strung along the spine of the Rockies. Curious, I did more research, and learned that these glaciers were so named because of their contents — they had entombed wayward grasshopper swarms centuries ago. If the grasshopper corpses were actually locusts, they might provide a clue as to how these insects disappeared.
At first, it looked like the search for clues would be futile. My students and I started at Grasshopper Glacier above Cooke City, Mont., which had once been promoted as a tourist attraction, accessible by horse, and later, by jeep. The insects in that glacier were badly decomposed, as the ice had been melting. Another Grasshopper Glacier in the Crazy Mountains yielded beautifully preserved grasshopper specimens, but they were no more than a few years old.
For the next two years, we searched the ice plastered on the flank of Beartooth Peak, near the Wyoming border. Again, we collected the mangled body parts of long-dead grasshoppers and honed our forensic skills. The fragments matched those of the Rocky Mountain locust, but we lacked the definitive evidence that could only come from intact, whole bodies.
Finally, after four years of fruitless searching, following up on a tip from colleagues at Western Wyoming Community College, we found the mother lode. High on Knife Point Glacier in the Wind River Mountains, with Gannett Peak looming in the distance, a frozen graveyard was emerging through the ice. The tiny bodies had been crushed, but they were intact. There was no doubt that these were the corpses of Melanoplus spretus. We’d found the locust.
We eventually recovered 130 largely intact remains. Each was catalogued, dried for preservation, and individually stored for future study. Based on subsequent radiocarbon dating and analysis of the glacier, we surmised that in the early 1600s — around the time that the Pilgrims landed at Plymouth — a swarm of Rocky Mountain locusts was blown into the mountains, probably from the river valleys 100 miles to the northwest that are now part of Yellowstone National Park.
Scattered across the glacier in a seething carpet of brown-green bodies, some of the locusts may have escaped and continued their journey, but millions were probably immobilized by the cold. In the course of summer melting, rivulets washed them into the crevasses that split the top of the ice field. With time, they were frozen deep in the glacier and slowly transported down the side of the mountain.
Today, about 750 feet downhill from the crevasses, the slope flattens rather sharply, and the ice — in a slow-motion version of the rapids at the base of a waterfall — becomes turbulent, churning its contents to the surface. For the first time in nearly 400 years, the locusts have come back into the light.
The study of their corpses, along with careful historical research and ecological sleuthing, allowed us to slowly piece together the story of a remarkable creature. Perhaps most interesting, the story of the locusts challenged a basic tenet of conventional ecological wisdom.
The standard textbooks of applied entomology suggest that insect outbreaks are evidence of a disturbed or out-of-balance ecosystem. Like a well-behaved child or a good worker, a species should refrain from extreme outbursts. This Victorian-era view of the ideal emotional state — perhaps also the legacy of Darwinian uniformitarianism, which emerged as a reaction to the church’s reliance on catastrophes to explain the history of the Earth — has lived on in our perception that an outbreak or crash of population is a sign of a troubled species.
Not so with the Rocky Mountain locust. The leitmotif of this insect was its phenomenal flights of reproductive fancy, with manic swarms sweeping over the Plains only to subsequently collapse into pockets of exhausted survivors. Evidence of this was embedded in the annual layers of Knife Point Glacier, which revealed a pattern of locust outbreaks extending centuries prior to European alterations of the Western landscape.
All too often, we are alarmed by nonconformity because of our desire to live in a predictable world, our social and political intolerance of radicalism, our economic pursuit of steady growth, and our Protestant ideal of moderation. It is true that people, species and ecosystems can manifest extreme dynamics during times of trouble. But the locust shows that erratic, even explosive, population dynamics do not necessarily reflect dysfunctionality – nor do they require meddling from humans.
I suppose I shouldn’t have been surprised that our work on the Rocky Mountain locust was at first met with skepticism.
Along with my students and colleagues, I submitted our work to a scientific journal; the paper described what we had found, including the condition of the glacier, the location of deposits, the types of insect parts we had extracted, the radiocarbon dating, and the analysis that led us to believe we had recovered the remains of the Rocky Mountain locust. As the first study of insects exhumed from a glacier in nearly 50 years, we hoped that the manuscript would be well received. It was rejected.
On behalf of the reviewers, the editor explained that the study did not constitute a controlled experiment. "You have mistaken natural history for science," she wrote. But I suspect that the reviewers’ doubts ran deeper. One of the long-lasting debates surrounding the Rocky Mountain locust had been whether it was truly a species or simply the migratory form of a species that still exists but no longer swarms. The arguments were phrased in terms of scientific evidence, but I could not help wondering if the debate was grounded in a visceral disbelief that such an enormously abundant creature could disappear from the face of the earth in a matter of a few decades.
I could understand the misgivings. The glacier had revealed a great deal about the life of the Rocky Mountain locust, but frustratingly little about its death.
At the time of the insect’s disappearance, there were no synthetic carbon-based pesticides, no modern earth-moving equipment, not even chain saws. Settlers fought back with what tools they had, from flooding to fire to dynamite. But this hand-to-hand combat didn’t make a dent against an enemy that was billions strong. So one could only conclude that if humans had wiped out the Rocky Mountain locust, they had done so inadvertently. In other words, the most spectacular "success" in the history of economic entomology — the only complete elimination of an agricultural pest species — was a complete accident.
How could an unwitting cohort of early settlers, concentrated in a relatively limited area of the vast Great Plains and Rocky Mountains, have wiped out an insect that during its outbreaks ranged from Canada to Mexico and from Utah to Iowa?
The break in the case came during my teaching. In an effort to work some interesting (i.e., nonmathematical) elements into my Insect Population Biology course, I dug into the ecology of the monarch butterfly. Much like the locust, this species distributes itself across the face of the continent. And much like the locust, the monarch is poised on the edge of extinction in North America.
How could a butterfly that fills roadsides and fields from Texas to Maine be in jeopardy? After migrating northward each summer, this species returns to overwinter in the remote mountains of Mexico. Its populations stretch across North America, only to collapse back into a few shrinking pockets of forest. Loosed on these pockets, a logging crew armed with chain saws could put an end to this magnificent butterfly in a matter of weeks.
There was the answer, staring me in the face. Like the monarch butterfly, the Rocky Mountain locust was tremendously vulnerable at certain times in its life. Between outbreaks, the locust hid out in the river valleys of Wyoming and Montana — the same river valleys that settlers had discovered were best suited for farming.
By converting these valleys into farms — diverting streams for irrigation, allowing cattle and sheep to graze in riparian areas, and eliminating beavers and their troublesome dams — the pioneers unknowingly wiped out locust sanctuaries. They destroyed the locust’s equivalent of Mexican forest wintering grounds. They doomed the species.
I’d pretty well wrapped up the case of the locust’s disappearance. Our studies were eventually published in respected scientific journals, and my explanation of the locust’s extinction became the most widely accepted theory.
But I was not quite ready to give up on finding a few still alive. Although it was a long shot at best, in the 1990s my students and I ventured into the last possible haunts of the locust, the river valleys near Yellowstone National Park where the soils had never been turned, cattle had never grazed, and the waters still flowed freely. Few entomologists had systematically collected grasshoppers in these remote valleys, so a glimmer of hope remained. Until I had tried and failed to find this creature on my own, I was reluctant to declare that it had truly vanished from the face of the earth.
As we scoured the meadows along the Yellowstone River, armed with sweep nets, I imagined what might happen if we found a lost population of locusts. Regulatory officials might advocate their destruction, fearing a revival of the swarms of the 1800s. Even the vaunted Endangered Species Act exempts pests from protection, so this remnant population might well be accorded the same status as the last vials of smallpox.
However, in my fantasy scenario, I liked to imagine — not without irony — that economic entomologists would point out that "pest" is a label that can be applied only under appropriate conditions: A population of Rocky Mountain locusts that had not bothered us for a hundred years could hardly be termed a pest. From the environmental camp, a few voices might call for protecting these insects as important components of a native ecosystem. Some might point out that the Rocky Mountain locust could serve as a reminder that humans have to share this world with other species — including those that we have not tamed or controlled. Others might cite its powerful place in the history and folklore of the West.
But in the end, I wondered, would our decision be any different from that which the early pioneers would have made, had they realized that they had reduced the locust to a tiny final fragment of habitat? If we struggle so mightily over whether we should save the last bits of old-growth forest and the few untrammeled tracts of the Arctic, what hope would a locust have?
As word of our search spread, a few leads developed. At one point, there was a report of a number of grasshopper specimens collected in North Dakota that were similar to the Rocky Mountain locust. But they turned out to be the migratory phase of another, closely related grasshopper species. In the end, we came up empty-handed. While my heart keeps me half-looking for survivors whenever I hike the river valleys that cut through the Rocky Mountains, my head has given the locust up for dead.
We usually conceive of the world in terms of material things — for example, we define a species as a bunch of individuals with the capacity to successfully interbreed. Ecology, however, is beginning to slowly shift focus, tentatively exploring what the world would look like if process, rather than matter, were the basis for reality. What if we defined a species in terms of its life processes? What if we suggested that a thing is what it does?
In this light, the Rocky Mountain locust was an immense, aperiodic process of energy flow, linking life-processes across a continent. And in this light, there is no doubt that this species was extinct by the late 1800s. Even if I found a remnant population and we managed to conserve the last Rocky Mountain locusts in a zoo, they would no more be their original species than the condors that can never again know the vast, unbroken expanses of California’s foothills. Unless these insects could once again blacken the skies of the West, they would, in fact, be nothing more than Rocky Mountain grasshoppers.
Setting aside the current wave of extinctions, the average species of bird or mammal has a life expectancy of about 10 million years, according to ecologist E.O. Wilson. If this is true, Homo sapiens is still in its adolescence — a time during which individuals of our species pay little heed to their own mortality. To teenagers, the notion of dying is hopelessly irrelevant, a fact that must contribute to the foolish indiscretion, misplaced courage and irrational risk-taking that too often end in accidental death.
Our species seems to be manifesting these same tendencies at this point in its development. But there are older, wiser voices to be heard in our biological community, including that of the Rocky Mountain locust. Dr. Child’s record swarm of 1875 probably contained in the neighborhood of 10 billion insects, which is disconcertingly close to the current human population on the planet. Having reached 6 billion people, we need only look back at the locusts that once blackened the skies of North America to realize that the future of a species is no brighter for its great numbers.
But, you might argue, human beings are the ultimate generalists, capable of adapting to a wide range of environmental challenges or, if times get really tough, of moving on to the next best place. However, the Rocky Mountain locust was also a generalist that consumed no fewer than 50 kinds of plants from more than a dozen different families, not to mention — when hunger demanded — leather, laundry and wool still on the sheep. In contrast, human beings derive most of our food from just three plant species — corn, wheat, and rice — found in a single family.
Moreover, if the body size of the Rocky Mountain locust was increased to that of a human, available records suggest that it would be capable of traveling 36,000 miles — approximately the circumference of the Earth. It appears that being a highly mobile generalist is little protection against extinction.
Still, the Rocky Mountain locust had an Achilles’ heel — the ecological bottleneck that allowed a small contingent of settlers equipped with horse-drawn plows, axes, and shovels to do them in. Humans don’t seem to have this sort of bottleneck. Or do we?
On our last day on Knife Point Glacier, my students and I set a drift net in one of the hundreds of rivulets that rushed down the face of the ice. In just 24 hours, we collected 140 fragmented remains of the Rocky Mountain locust. At this rate, at least 20 million corpses have melted from the glacier since that day in 1990, washing into Dinwoody Creek and from there, perhaps, into the Wind River.
It’s not just the churning of the glaciers that is bringing locusts back into the light. The glaciers of the Rocky Mountains are melting at a phenomenal rate. Based on our studies of Montana’s grasshopper glaciers, the glacier north of Cooke City has receded 89 percent since 1940; the glacier in the Beartooth Mountains is 62 percent smaller now than in 1956; and the one in the Crazy Mountains has diminished 90 percent in the last 16 years.
Our discovery of grasshopper remains coming to the surface of these glaciers is a direct result of global warming.
As ecological processes on the planet change through human activity, we find ourselves increasingly brought into conflict. Shifts of human populations away from flooded seaboards and desertified landscapes, burgeoning populations in cities and their marginal slums, wars over oil, struggles for access to water, and fights to save remnants of disappearing habitats are all on the horizon.
In these troubled times, sociologists tell us that humans increasingly seek solace. We are drawn to our sacred spaces: churches, synagogues, temples and — for some of us — serene mountain valleys, where rivers cleanse our anxious minds. Just as the locust was able to find a safe refuge, where it could rest and revitalize, we need our sanctuaries. But is it possible that these very havens — our wilderness preserves, ungrazed meadows, clear streams — might prove to be ecological bottlenecks?
A century ago, human alterations of the environment caused the demise of the Rocky Mountain locust, and today, the ghosts of these insects warn us of an even more serious threat to the natural world. As our current environmental crisis exposes our past act of accidental destruction, one can only wonder what else we can learn from the Rocky Mountain locust.