Locust (39 page)

Recent excavations of fossil and subfossil bones on Pacific Islands have revealed an incredible story of extinction. With the arrival of the Polynesians in the outer Pacific, from Tonga in the west to Hawaii in the east, at least half of the species of endemic birds disappeared. Hopscotching from island to island in single outrigger or double canoes, these first settlers left a record of environmental destruction in their wake. The eminent conservation biologist Edward O. Wilson
summarizes this period of human expansion quite simply: “The voyagers ate their way through the Polynesian fauna.” For example, on Eua (in present-day Tonga) the colonists were greeted by the squawking and twittering of 25 bird species, of which 17 were permanently silenced. Of about 100 species of birds that lived on Hawaii before the arrival of humans, the native people extinguished half before the arrival of Captain Cook in 1778, and another 15 or so have disappeared since. But islands are not the only landforms subject to the devastation of primitive people.

Shortly after the arrival of humans in North America, nearly three-quarters of the large mammal genera became extinct. Mammoths and ground sloths had flourished for 2 million years, but within 1,000 years of our arrival these creatures disappeared. The story is the same for the largest birds that once roamed the continent. Climatic shifts might have played some role in these extinctions, but the general consensus is that global warming during the Pleistocene was, at best, an accomplice of the human hunters. Chain saws, synthetic chemicals, and hydroelectric dams might be the modern, high-tech weapons in the war against nature, but it appears that canoes, snares, and spears were entirely adequate to the task.

The means of environmental disruption available to the European settlers of the Rocky Mountain region were not much more sophisticated than those of the first people who colonized this land. Wherever the locust might have begun to increase in numbers along the river valleys, the farmers probably employed direct means of suppressing the insect. But from the accounts of the settlers and the records provided by Riley, it appears that such battles were scattered and the skirmishes were minor. Rather, the farmers waged a sort of unwitting guerrilla warfare, an insidious assault on the supply lines and homelands of the locust.

 

In 1866, General John Pope held out little hope for agriculture in the arid West. The only cause for limited optimism was in the Rocky Mountain region, where, “the streams being more numerous, and the timber more abundant, it is practicable to form settlements and to cultivate the valleys of the streams by irrigation.” This glimmer of hope
soon became a radiant beacon for the settlers seeking prosperity. A century later, the renowned western historian Gilbert Fite described precisely this course of events: “Whenever possible, settlers located on or near a creek or river in order to have water for livestock and irrigation.” By the 1880s, the competition for the West’s key resource was becoming downright nasty: “Water was becoming scarce at critical times during the growing season, valleys were becoming crowded, and conditions for newcomers were discouraging.”

Irrigation was the lifeblood of agriculture in the Rocky Mountain region. Of the 50,000 farms in 1890, 70 percent were operated by irrigators—about 2 million acres were regularly flooded. A decade later, more than 5 million acres in the Rockies were being irrigated by 70,000 operators. Our most generous estimate of the locust’s distribution during its recession periods was 2 million acres in the montane river valleys of the West. In this context, it seems entirely possible that the vast majority of the insect’s sanctuary was saturated by pioneer farmers on a yearly basis. But would this have been lethal?

In combating the locust, Riley understood that habitat modifications could have far greater effects than desperate acts of direct confrontation, such as thrashing, poisoning, or crushing the invaders. He advised, “When irrigation is practicable, as it is in some of the ravaged parts of Colorado, let the ground be thoroughly inundated for a few days, and the eggs will lose vitality and rot. . . . Experiments prove how soon they succumb to excess moisture.” As he reviewed the various primitive tools available to defend agriculture from these rapacious creatures, he became increasingly convinced of the value of water.

Sixteen years later, in one of his last publications on the locust, Riley remained convinced that irrigation was one of the most economical and effective methods for suppressing
spretus
. By this time, he understood that water represented both life to the farmer and death to the locust:

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.