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  17 September 2014  |  Vol: 4 facebooktwitterrss  
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The Big M-T
 
The Mysterious Disappearance of the Rocky Mountain Locust
 



The greatest insect pest the world has ever known is extinct. Or is it?

Among the iconic images of an earlier American West are skies filled with flying locust that descend upon the crops of pioneer farm families who, in spite of their best efforts, are ruined by the plague. Grasshoppers seemingly on steroids eat anything in sight—the horse blankets thrown over the family garden, shovel handles, clothes left out on the line. The noise of it all is sickening. Then the horde lifts off and moves downwind to wreak havoc upon the next colony of immigrants.

Prairie journals of the day documented the phenomenon, most famously Laura Ingalls Wilder’s On the Banks of Plum Creek from The Little House on the Prairie series. Modern cultural efforts such as the Terry Malick film, Days of Heaven, also offer disturbing portrayals of these plagues of locust on the North American prairies.

If it all seems just a little far-fetched, it’s probably not. A flight of locust in 1874 is believed to be the largest mass of living insect matter ever witnessed by modern man. Tracked by the then-new technology of telegraph, the main storm of that plague was measured at 110 miles wide and 1,800 long, stretching from the Canadian plains to the Texas border, moving easterly toward the Mississippi River. Periodic outbreaks of locust on the Great Plains were a major obstacle to agrarian settlement of the prairie frontier in the mid- to late-19th Century, and frontier farmers risked starvation behind an infestation.

The living, breathing tonnage of these insects in the 1874 outbreak has been compared to that of the American bison of the same era, and possibly was just as influential on the ecology of this vast region. These insects sustained animal and human life—yes, some aboriginal tribes ate locusts—while churning huge quantities of organic matter into the carbon cycle.

The Rocky Mountain locust remains today only as a cultural relic. Within 30 years of the 1874 flight the species had disappeared entirely from the North American landscape. Vanished. The last documented living specimens of Melanoplus spretus, the Rocky Mountain locust, were observed and collected near Brandon, Manitoba, in 1902.

This insect is very likely extinct, perhaps never again to consume a single kernel of wheat from the North American breadbasket. Yet, as I write this, Egyptian farmers are burning tires to dissuade locusts blown in from the Sudan. Israel is similarly affected. The cradle of agriculture and civilization along the Tigris and Euphrates Rivers is still occasionally visited by locust swarms. Yet North America has joined Antarctica as the only continent without at least an occasional flight of locust.

What happened here?

Over the past century, this disappearance has baffled entomologists and ecologists. The collapse came, after all, before the advent of synthetic insecticides, such as DDT, or even modern farming techniques. Consequently, the leading theory for the crash seems vaguely unsatisfactory to many in the broader community of insect study. That theory holds the species was wiped out by a series of developments that played out between 1875 and 1900 in the valleys of the upper river basins along the Northern Rockies—the natural home range of the locusts between irruptions out onto the prairies. Loss of beavers caused by the earlier fur trade era increased flooding, for example. The valleys filled with foraging cattle and sheep and irrigated crops such as alfalfa supplanted native grasses in the bottomlands. The gold and silver mining era brought a comparatively large number of people to the valleys and local agriculture burgeoned to support the human populations.

According to this theory, the environmental disturbance to the montane valleys arrived as the insects had retrenched into a natural nadir—a population bottleneck—awaiting the next drought and re-emergence as migratory locusts. Grasshopper egg clusters were trampled by domestic ungulates or flooded out by spring torrents or summer irrigation. The already isolated populations of proto-locust grasshoppers, spread out among valleys along the spine of the continent, could not hold out and M. spretus became extinct.


A color rendering from the 19th Century based on a drawing by Charles Valentine Riley
.

Well, that’s the current leading theory, anyway, and its main formulator and proponent is Jeffrey Lockwood, an entomologist and grasshopper specialist out of the University of Wyoming. Lockwood studied and published extensively on the Rocky Mountain locust over a career that spanned more than 20 years. He recently transferred to UW’s philosophy department and focuses these days on writing fiction, non-fiction, and essays. But his 2004 book, Locust, offers a natural history of the insect and details the steps leading to this extinction theory.

Scientists working around the turn of the last century were understandably late to grasp the possibility that this particular grasshopper might be extinct. Major outbreaks tended to occur roughly every eight to ten years, so long periods without a regional sighting were not considered unusual. As the premier pest of the continent’s midsection, out of sight was out of mind. World War I intervened, of course, as well as the Great Depression. When scientists returned to the absent insect toward mid-century, a popular theory held that migratory locusts were a form of commonly-found grasshoppers that emerge as the stresses of drought and overpopulation force them to migrate en-masse from native ranges. Studies of locust in central Asia and elsewhere had revealed these traits and behaviors.

Further, many felt the Rocky Mountain locust and its proto-locust grasshopper was not a distinct species. Rather, the locust was thought to be a particularly gregarious and migratory phase of a grasshopper still common throughout the West—M. sanguinipes. As environmental conditions once again became optimal, it was thought, a form of locust might emerge from this common grasshopper.

In the mid-1980s, Jeffrey Lockwood and others began to look to molecular analysis to unlock some of the mysteries surrounding the disappearance of the American locust. Disturbingly, although once estimated to occur in the trillions, perhaps fewer than 400 professionally-preserved specimens of Rocky Mountain locust remain in university and government collections. (The photographic record is also rather sparse.) Most of these specimens are dried and mounted and as such are somewhat degraded for DNA analysis. Lockwood and his associates out of Laramie turned to the famous “grasshopper glaciers” that persist along the most remote upper stretches of the Continental Divide.

*

I’m looking at an old photograph of myself at Grasshopper Glacier on the Beartooth Plateau above Cooke City just north of Yellowstone Park. My girlfriend, Liz, and I are teenagers and we look it. It’s August of 1973 and the trek up from Goose Lake has been a breeze for our fellow summer employees in Yellowstone. The surface of the glacier that day is littered with half-alive and dead grasshoppers recently lifted up by winds sweeping over the Beartooth benches. Local legend even then indicated that huge quantities of frozen locust were buried deep within Grasshopper Glacier.

In 1987, Jeffrey Lockwood and his colleagues tried this glacier first, hoping to find locust specimens. What they found was a glacier greatly receded. Older grasshoppers seemed to exist in only tiny fragments with lots of species intermingled. After several other false starts with glaciers in the Crazy Mountains, his team was able to find intact locust specimens at Knife Point Glacier in Wyoming’s Wind River Range. Over several visits, he and his colleagues collected whole locusts as well as pieces and submitted them for DNA analysis and carbon dating.

The DNA analysis was performed by two Canadian colleagues who reported results in a professional journal in 2003. They obtained intact and partial specimens from Lockwood’s Knife Point Glacier expeditions, which were carbon profiled to be about 400 years old. Dried museum specimens from late 19th century locust outbreaks were also examined. Related grasshoppers, including the common M. sanguinipes, were tested along with a couple of non-related locusts from other continents as a control.

The DNA study concluded a couple of things. First, Melanoplus sanguinipes—the common meadow grasshopper—and M. spretus are most probably not “phase transforms” of one another. In fact, the study showed the Rocky Mountain locust is more closely related to yet another common grasshopper, the wide-ranging spur-throated grasshopper M. brunerus, which some researchers feel is one of the hoppers that filled the ecological vacuum left by the extinction of its close relative. (Indeed, heavy agricultural damage by the spur-throated hopper was reported in the early 1920s.) Secondly, whatever caused the disappearance, it was likely not a problem of genetic diversity, since samples from the presumably robust 400-year-old specimens compared closely with those collected near the time of the population collapse.

The study is seen as the strongest evidence to date that the Rocky Mountain locust grasshopper is a discrete species.

So a question remains, is the Rocky Mountain grasshopper and its locust transform, M. spretus, an extinct species? One well respected authority argues no, it is not. Rather, the species lies dormant, hidden in remote mountain valleys awaiting favorable conditions to remerge as a fully migratory locust.

“I can’t believe spretus is extinct,” Daniel Otte wrote me in an email recently. “But where to look for it?”

Otte is senior curator at the Academy of Natural Sciences at Drexel University in Philadelphia and is well known for his studies on grasshoppers and crickets as well as on the origin of insect species. According to his official website, he has discovered and named roughly 1,600 species. He is the author of a two-volume atlas, North American Grasshoppers, published by Harvard University. His opinion in this matter is not taken lightly. Although re-emergence after a century in remission is widely viewed as extremely unlikely, Otte wrote me recently that he and graduate students will conduct fieldwork somewhere in the Rockies this summer in search of the latent Rocky Mountain locust.

*

A detailed government monograph shows just how well understood the life cycles and habits of this insect had become by the late 1870s. The U.S. federal government and the agrarian Midwestern states had a powerful common enemy in the Rocky Mountain locust and both sought knowledge as a key to a successful battle. Charles V. Riley, the first state entomologist for Missouri and later head of the newly formed U.S. Entomological Commission, was just the person to provide that knowledge. Riley, a gifted illustrator and tireless investigator, worked for ten years to detail the natural history and habits of the Rocky Mountain locust, collecting specimens from six western states and territories. His definitive 1877 report is entitled: The Locust Plague in the United States: Being More Particularly a Treatise on the Rocky Mountain Locust or So-Called Grasshopper, as it Occurs East of the Rocky Mountains, with Practical Recommendations for its Destruction.

Riley was an early observer of the traits grasshoppers express as they overpopulate and pressures to compete for food resources become intense. These grasshoppers go through an additional molt—a change of clothing and character, if you will. The grasshoppers emerge with greatly elongated wings, bland colorations, and an appetite for travel. Even the sexual drive becomes repressed as a plague emerges and takes initial flight. This final destructive phase becomes the Mr. Hyde to the more benign Dr. Jekyll of the M. spretus grasshopper. This full-blown locust phase was the cause for so much agricultural devastation in the 19th Century as prevailing winds aggregated the nomadic swarms.


A woodcut from the 19th Century from Charles V. Riley’s The Locust Plague in the United States.

Riley tracked the locust back to its incubation valleys, including the Three Forks of the Missouri and the areas along the upper Yellowstone River. Riley notes that bears in this region—presumably grizzlies—had been observed feasting on newly hatched grasshopper larvae. He writes that the 1874 plague that reached Missouri “have their origin in the vast plains regions of the northwest lying east of the mountains, in Montana, Dakota, and the Saskatchewan and Red River countries of British America.” He speculates the “origin of swarms that devastate the Pacific slope is probably in the similar high plains regions of Washington, Idaho, and Oregon.”

The self-taught Riley observed that although swarms procreate and lay eggs on their fabulous journeys, each subsequent generation, while still harmful to crops, becomes less viable, more decrepit, and less able to prosecute sustained flights. He conducted experiments that showed grasshoppers hatched in the mountains were 25 to 50 percent stronger than those hatched in Nebraska or in states further eastward. He further noted a high prevalence of mites and other parasites on the grasshoppers hatched in the great swaths of the temporary zones. The locust cannot “thrive or perpetuate itself in the Mississippi Valley,” he wrote, confidently. “It will never do serious harm east of the ninety-fourth meridian.” The insect could only truly sustain itself within a subalpine home range of “five to eight thousand feet or more above the sea level.”

That observation seems central to home ranges in the mountain valleys along the Rocky Mountains. But could that much native range have been disturbed during the pioneer era of the late 19th Century? Proponents of the extinction theory would seem to think so, but the absolute negative of extinction is difficult to prove. The mastodons of the Ice Ages are clearly extinct; the Passenger Pigeon is as well. The raven-sized Ivory-Billed woodpecker of the southern swamplands was thought extinct by 1940, but a glimmer of hope remains as sound recordings and unverified sightings continue to trickle in. Different species of grasshoppers can be extremely difficult to discern visually, and some argue adequate surveys for M. spretus have not been conducted. Even Jeffrey Lockwood steps back a bit from a full-out declaration of extinction in his book, Locust. Lockwood hints that colonies may survive in isolated settings such as the Hayden Valley of Yellowstone Park.

“I remember one female with spectacularly long wings,” he writes about a collection foray into the park. Long transparent wings are a visual clue to the locust morphology. “I captured several similar individuals from a meadow… I think I know who they were, so I released them back into the field.” The awkward syntax aside, even the leading extinction theorist offers an escape route, however well concealed.

In a more recent professional paper, Lockwood raises the possibility that should remnant populations be found, would they be protected by the Endangered Species Act? He believes not, since agricultural insect pest species are generally not viewed as eligible for protection. A re-discovery of the Rocky Mountain locust would indeed prove problematic on several fronts. Lockwood compares the possibility to the smallpox virus. Once a deadly scourge the world over, the smallpox virus exists today only in a couple of secure laboratory settings, such as the Centers for Disease Control. Occasionally, calls arise to destroy the remaining viruses to keep them from falling into control of terrorists. If M. spretus were to be found in hiding, rest assured credible constituents would quickly aggregate to fight to preserve the colonies alongside those who would annihilate them. Agriculture in the U.S. and Canada may have unwittingly and unknowingly contributed to the collapse of the species a century ago, but—as with smallpox—the prospect of its return is unacceptable.

The successful DNA extraction for M.spretus from the disappearing glaciers is perhaps more analogous to the smallpox virus. Just this morning’s news features a report that extinct species are under serious consideration for recovery through cloned births by closely related surviving species—the so-called Lazarus Project. In theory, the Rocky Mountain locust might be recovered by introducing genetic material into closely related species such as M. bruneris, the common spur-throated grasshopper. Lazarus Project technology is already well underway, but good luck securing research grants to bring back the Rocky Mountain locust.

Still others in the community of insect science believe none of this matters all that much. When environmental conditions once again become optimal, a form of locust may very well emerge spontaneously from common grasshopper suspects such as the spur-throated varieties or M. sanguinipes, or perhaps hybrids that emerge as species capable of transforming into locust. These families of insects have somehow endured repeated Ice Ages of the Pleistocene Epoch, out-survived megafauna from mastodons and New World camels to free-roaming bison, and today seem to survive quite nicely amidst powerful pesticides and genetically manipulated crops.

As for me, I’d like to spend some time with Dan Otte and his research team this summer combing the high mountain meadows in search of the mysterious missing colonies of the greatest insect pest the world has ever known. If we find any, it’d be something to write home about.   -TBM

Paul J. Driscoll is a public information specialist with the Montana Department of Environmental Quality.  In July of 2012, his equally fantastic report on Tiger salamanders, titled, "Axolotls," is in our archives and linked here.

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