But for farmers, the point of irrigation was to grow crops, not to drown locusts. And so we must also consider what was being sown. The plants that were replacing the montane meadows may have been lethal in their own right.
The studies conducted by Charles Brett in the 1940s had demonstrated that alfalfa was deleterious to sanguinipes—and perhaps by extrapolation to spretus. Bob Pfadt’s systematic experiments had isolated this detrimental effect to the period of nymphal development in sanguinipes. Recall that Pfadt had questioned the contention that alfalfa was lethal to the Rocky Mountain locust, as Brett had provided no compelling evidence that the locust had actually encountered this plant. Riley’s exhaustive list of items eaten by the locust would have been funny, if it hadn’t reflected the rapacious appetite of the creature that drove so many pioneers to despair.
The litany of plants consumed by the locust fills several pages in Riley’s reports. However, amid this catalog of gluttony, alfalfa is not mentioned. The only reference in this regard is Riley’s discussion of the legumes—the plant family to which alfalfa belongs: “Of leguminous plants the pods are preferred to the leaves, which are often passed by. . . . The dislike these insects show for leguminous plants is well known, and a crop of peas will often succeed where they abound, when all else is ruined.” Riley agreed with his colleague G. M. Dawson, who suggested that from a Darwinian perspective the relative rarity of legumes among the native plants of the Great Plains might account for the insect’s lack of affinity for peas and their relatives. For whatever reason, a creature that greedily consumed tobacco, only to die shortly after from the nicotine poisoning, avoided legumes whenever possible.
Most important, Bob Pfadt had persuasively argued that even if alfalfa had been detrimental, a species with the immense distribution of the locust surely had plenty of options when it came to feeding. Gurney and Brooks also dismissed Brett’s alfalfa theory on the basis of ecological scale. Alfalfa had not blanketed the prairies, so how could it have had any substantial effect on the locust? Of course, had these scientists understood the ecological bottleneck through which the locust was being squeezed in the final decades of the nineteenth century, their dismissal of Brett’s argument might not have been so facile.
Most of the land being irrigated in the Rocky Mountain region was devoted to the production of cereals and forage. According to the western historian Gilbert Fite, “Alfalfa became a leading hay crop in most of the irrigated valleys and provided feed for the growing livestock industry. Practically all the irrigation was for forage in Wyoming and Nevada, where ranching was the main agricultural activity.” Elsewhere in the region, cereal crops occupied one-fifth to two-thirds of the irrigated land. Perhaps alfalfa didn’t deliver the lethal blow to the Rocky Mountain locust, but it is clear that this crop may have been an important accessory to murder. In the end Charles Brett might have been much closer to cracking the case than his successors ever imagined.
Not only was alfalfa apparently distasteful or even harmful to the locust, but this crop would also have conspired with irrigation to create an ecologically deadly scenario. Alfalfa is one of the thirstiest plants in agriculture, requiring about two-tenths of an inch of water per day. The continuous irrigation needed to grow alfalfa would have made conditions disastrous for the Rocky Mountain locust.
Saturating the soil probably killed off locust eggs in some fields, and patches of alfalfa might have hindered the development of the nymphs that did manage to hatch. But the unwitting pioneers had even more devastating ways of transforming the river valleys from cradles into graves.
The two greatest implements of ecological change in North America were arguably the plow and the cow. Vast tracts of prairie were plowed by farmers using oxen, mules, or horses. The tallgrass prairie once spanned parts of fourteen states, blanketing 142 million acres—an area nearly the size the Texas. Well over 90 percent of this ecosystem was turned under or paved over. The soils of shortgrass prairie or steppe were too poor and dry to support crops, so much of this ecosystem was spared from the plow. Instead, it was consigned to intensive grazing by cattle. Today, two-thirds of the western rangelands are in fair to poor condition, a legacy of abuse and neglect that peaked at the end of the nineteenth century. A few ecosystems suffered a one-two punch both under the moldboards of plows and beneath the hooves of livestock. Such was the fate of the montane river valleys.
An acre is a bizarre unit of measure, but like most English units what it lacks in sensibility, it makes up for in history. To be both precise and obscure, an acre is one furlong in length and one chain in breadth. A furlong is a distance of 220 yards. This value is historically derived from the longest stretch of heavy soil that a yoke of four oxen could pull a plow through before they had to rest. Hence, furlong is the shortened form of furrowlong. A chain is one-tenth of a furlong—a sort of early capitulation to metric notions. The result of multiplying a furlong by a chain is 4,840 square yards—the area encompassed by an acre. Although a furlong has agricultural meaning, one might reasonably ask why the English nobles multiplied this distance by a chain to derive an acre. An acre turns out to be the area that a medieval plowman was required to till in a day. So, the plow and the acre are intimately related.
Despite the advances in technology between the Middle Ages and the Industrial Revolution, the pioneer farmer in the 1800s could plow no more efficiently than his medieval counterpart. Agricultural engineering had provided some advancements, but the rate at which the sod could be turned changed very little in 600 years. At this rate of work, the 50,000 farmers tilling the soil of the river valleys in 1890 could have plowed 5 percent of the Rocky Mountain locust’s habitat in a day—if we use a million acres as the midpoint estimate of the creature’s area of occupation within the Permanent Zone.
Plowing and harrowing had opposite physical effects, but in either case the biological result was the death of spretus. In his 1877 synthetic distillation of Rocky Mountain locust biology, ecology, and management, Riley endorsed plowing and raved about harrowing: “So satisfied have I been for some time that systematic harrowing of eggs, or their exposure by other means, in the fall, is the best work that can be done, that I have earnestly urged its enforcement by law whenever the soil in any township is known to be well-charged with eggs.” Normally lying a couple of inches beneath the surface, when plowed under the eggs were unable to receive the warmth necessary for development. And even if they did hatch, the emerging nymphs would be unable to reach the surface. Harrowed to the surface, the eggs were exposed to predators and scavengers, including everything from hungry birds and skunks to foraging ants and beetles. More important, the eggs were no longer insulated from severe weather by a blanket of soil. Riley found that alternate freezing and thawing—typical of springtime in the Rockies—was particularly devastating to the embryos. If they survived these temperature swings, they would almost surely succumb to water loss. For such tiny creatures as locust embryos, desiccation is the gravest physiological threat—and exposure to the brutally dry winter air of the Rockies would have been lethal. But as deadly as the plow was to the locust, there was an even more destructive force at our disposal.
The ultimate limit of the plow’s capacity to transform the landscape of the pioneer was that a hulking creature had to drag it through the soil and a sweating human had to guide its path. This trio of animal, human, and machine constrained tillage to the number of hours that even a dedicated farmer could put into such backbreaking labor. The domesticated grazing animals of the pioneers, however, could work continuously in altering the ecology of the river valleys. Attached to a plow, an ox could only turn over so much sod, but left on its own, a cow could graze the floodplains, meadows, and uplands with abandon.
Between 1870 and 1884, the number of cattle in the western states grew by almost tenfold, from about 450,000 to nearly 40 million animals. In Wyoming, the number of cattle increased during this period from 8,000 to more than 1 million. Cattle outnumbered people by a factor of twenty
to one. Within a few years, land that had supported a cow and her calf on five acres had been so overgrazed that more than ninety acres were needed. And cattle weren’t the only culprits. In the rush to feed animals on public lands, sheep populations were also bursting at the seams. Steens Mountain in eastern Oregon serves as a particularly well-documented example. By the summer of 1900, there were 182,000 sheep packed into the mountain meadows laced with snow-fed streams. This stocking rate represented 450 sheep per square mile.
The grazing by cattle, in particular, was heavily concentrated along rivers and streams, precisely the habitats utilized by the locusts. Many of the breeds of cattle raised in the West were developed in the pastures of Europe, where water was in abundance. Unlike bison, these were thirsty animals, accustomed to plentiful water. The typical beef cow needed ten to fifteen gallons of water daily, and a dairy cow required nearly twice as much. The aggregation of cattle in the valleys dramatically altered these ecosystems.
Based on modern studies, we know that it does not take many livestock to rapidly degrade riverside vegetation. Cattle may not be the brightest creatures, but they know what tastes good. So while hanging out along the streams, they pick out their favorite plants and leave behind an odd and dysfunctional assortment of species. With the loss of deeply rooted vegetation that anchors the riverbanks, the soil begins to erode. And as the banks collapse into the river, the water becomes shallow and silty. In this manner, the falling banks and rising riverbed generate a self-perpetuating process. Through these mutually reinforcing activities, the structure of the channel degenerates, and the river is freed from its established borders.
Like a feral animal, the deep, calm river is transformed into a wild, churning flood. With chronic trampling by cattle and the acute surges of spring meltwater, the channel erodes into a broad, silty floodplain. This transformation is accelerated by the effects of cattle even far from the river valley. The compacted soils and overgrazed vegetation in the uplands renders the land incapable of absorbing and transporting the spring melt and summer rains. This runoff feeds an already bulimic watershed that binges on the winter snowpack and then purges the spring runoff. Without the capacity to buffer the inflow, a river becomes prone to spectacular flooding. According to Clarence Forsling, who headed the Department of Interior’s Grazing Service, the West has been plagued by “disastrous floods since the turn of the century because of overgrazing in the mountains.”
Although Riley spent years observing the Rocky Mountain locust and generated thousands of pages on the natural history of this species, he conducted only one set of experiments on the locust—and these related to the effects of flooding on the survival of the eggs. It was clear from his records during that winter of 1876 that Riley was not a research scientist, as his experiments followed no systematic design. He tried a haphazard set of conditions, submerging eggs for various durations and frequencies. His experiments also lacked controls, which is the sort of flaw that would be fatal to a junior-high science-fair project. That is, he failed to keep any of the eggs in natural or dry conditions during the winter to understand what the normal rate of hatching would be without his efforts to drown the embryos. Most of his experiments showed that submerging the eggs in the midst of winter, when the embryos were not developing, had little effect on survival. Of course, flooding egg beds in January would have been impractical, even impossible, throughout most of the locust’s range. In the mountain valleys, the rivers would have been frozen over and there would have been no potential for the inundation of the overwintering eggs.
Riley conducted only a few experiments in the early spring, but these results were most revealing. While locust eggs are in diapause (an entomological term for a state of lowered metabolism and arrested development analogous to vertebrate hibernation), they are not much harmed by flooding. But once development recommences in the spring, the embryos become sensitive to environmental conditions. As many as four-fifths of the eggs that were periodically submerged in March and April failed to hatch. Riley concluded that springtime flooding, when the eggs were near hatching, would be particularly detrimental to the locust. However, he never extended this conclusion to the Permanent Zone. Springtime would have been precisely the season in which the peak vulnerability of the locust coincided with the maximal likelihood of inundation in the degraded river valleys. For the Rocky Mountain locust, the conversion of the serene river valleys into churning floodplains would have been devastating in terms of both the erosion of soils that sheltered the eggs and the flooding of these habitats.
Riley also was confident in the effects of livestock trampling on the locust’s eggs. Thinking in terms of the farmers of the Great Plains, he recommended, “In pastures or in fields where hogs, cattle, or horses can be confined when the ground is not frozen, many if not most of the locust-eggs will be destroyed by the rooting and tramping.” In fact, locusts were reasonably willing to deposit their eggs in grazed fields, so they would have been particularly prone to this crushing and churning. Surely the eggs laid in the river valleys of the Rockies fared no better under the pounding hooves of livestock.
In his seminal paper on the phase transitions of locusts, Sir Boris Uvarov saw beyond the immediate biological meaning of his theory to its potential application in the realm of pest management. Although Uvarov was a consummate taxonomist and brilliant naturalist, he was firmly grounded in the practical world of agriculture. Toward the end of his 1921 paper, he speculated that suppressing the solitary phase of locusts might be more effective than pouring resources into battling the overwhelming swarms that swept across Africa and Central Asia. Uvarov wrote, “The theory of phases suggests the theoretical possibility of the control of migratoria by some measures directed not against the insect itself, but against certain natural conditions existing in breeding regions which are the direct cause of the development of the swarming phase.”
He clearly saw that the weakest link in the locust’s life history was between outbreaks. The time to strike was when the creature was hiding out in refuges. Uvarov briefly reviewed the situation in the Black Sea basin, where the river valleys had spawned immense swarms of locusts for centuries. After the 1880s, however, these breeding grounds had not generated another outbreak. Uvarov attributed this change in locust population dynamics to agriculture: “This is easily explained by the fact that the valleys of the Don, Kuban and Dnieper [river valleys in south-central Russia and Ukraine] were during the end of the last century more or less cultivated or, at any rate, their natural conditions were entirely changed by the persistent grazing of herds of cattle.” The failure to apply Uvarov’s insight to the case of the Rocky Mountain locust probably reflected both a mistaken sense of ecology (that studies of the Old World locusts had no relevance to North America) and a regrettable sense of arrogance (that Russian scientists had little to offer their American counterparts).
It seems that in the waning years of the nineteenth century, in river valleys 8,000 miles apart, the sanctuaries of locusts were being destroyed by farmers who were converting these habitats into fields of crops and grazing lands. The people who had been plagued for decades on the prairies of North America and for centuries on the steppes of Central Asia were simultaneously altering their landscapes in ways that would utterly transform the ebb and flow of life. Perhaps the only difference is that the river valleys of the Black Sea basin were ultimately more expansive than human industry could completely alter, whereas those of the Rocky Mountains were far more concentrated. And so today, while the farmers of the Great Plains know of locusts through the journals of their great-grandfathers, the farmers of Kazakhstan and Uzbekistan still know the visceral panic that comes on a summer day when the sky takes on the queer, dirty yellow hue of an impending storm, whose true nature is revealed by the shimmering flecks of 10 billion wings.
THE MOTIVE
The most difficult element in solving a century-old homicide—or would it be an “insecticide”?—is ascertaining the motive of the killer. Often, do
zens of people have the means and the opportunity to have done in the victim, so the case hinges on the element of motive. In the extinction of the Rocky Mountain locust, however, there appears to have been only one suspect present at the time and place of the creature’s disappearance and with the means to dispatch the victim. Therefore, pinning the blame on the settlers of the montane river valleys does not depend on finding a motive that separates the farmers from a collection of other suspects. However, we are rarely satisfied with simply knowing what happened. As humans we desperately seek to grasp why.
Of course, some events appear to occur randomly with no rational explanation. We don’t try to explain why a boulder careens down a slope and crashes onto a passing car or why a meteor smashed into the earth and snuffed out the dinosaurs. These seem to have been natural deaths, although rather tragic (in the case of the people in the car) or cataclysmic (in the case of the creatures at the end of the Cretaceous). Other events appear to originate from intentional acts—the assassination of John F. Kennedy, the serial murders of Son of Sam, the Columbine killings, and the extinction of the passenger pigeons, moas, and dodos. In these instances, understanding the motive helps us make sense of the world, and such insights might even allow us to avoid similar events in the future. The passing of the Rocky Mountain locust appears to fall into this latter category.
Although farmers might well question whether a pest should be protected, in the case of Melanoplus spretus we lost a keystone species that affected ecosystem processes on a scale equivalent to that of the bison. The locust was a “living fire” sweeping across the western lands, altering the nutrient cycle on a continental scale; a single swarm metabolically burned 4,000 pounds of vegetation an hour. The normal ebb and flow of energy, carbon, and nitrogen across the plains was lost along with the locust, and the ecosystem may not have yet recovered—given what we’ve learned about the consequences of altering fire regimes in western forests. What species may have been dragged down or critically weakened with the loss of the locust cannot be known because we have such a poor understanding of the biological diversity of the mountains and plains when spretus was thriving.
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