Locust (6 page)

An area of 198,000 square miles would encompass the combined areas of Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont. The swarm was probably an elongated stream of insects, but if it had been configured in a more familiar geometric shape, it would have comprised a square 450 miles on a side. The frontier of the New World was revealing marvels and terrors of a scale unparalleled in written history. The largest swarm of locusts outside of North America was reported in 1954, when fewer than a hundred square miles were covered by the notorious Desert locust in Kenya. No insect outbreak has ever approached the magnitude of the Rocky Mountain locust.

Trying to estimate the number of locusts in Albert’s Swarm is quite a challenge, but we can use some values from the scientific literature to approximate the size of the population. We might safely assume a settled density similar to that of the famed locust swarms in Africa (which involve a larger locust and likely have fewer individuals packed
into each square yard). If so, then the 1875 swarm that passed over North America had 3.5 trillion locusts, outnumbering the current human population on earth by a factor of 600 to 1. The swarm outweighed a man to the same degree that the biomass of a whale exceeds that of a mouse. Such quantities are unfathomable, but newspaper reports of damage from neighboring townships clearly substantiate Dr. Child’s account.

Although Isaac Cline never managed to associate weather patterns with locust outbreaks, we can now deduce the biological and meteorological conditions that conspired to create Albert’s Swarm. Scientists of the nineteenth century had begun to piece together the life cycle of the Rocky Mountain locust, and it appears that Albert’s swarm was qualitatively typical of the species. In an outbreak cycle, the locust swarms descended from the northern Rockies in early June. Carried by prevailing winds, these insects swept across the countryside, settling wherever there was abundant food. As the locusts advanced to the south and east, they began to mate, and soon after, females began laying eggs. Cylindrical clusters or “pods” of about thirty eggs were buried in the soil, and so the swarms left behind denuded fields riddled with eggs. The adult locusts would live for perhaps a couple of months, seeding the countryside with the next generation. The embryos would mature through the summer and then hibernate—a physiological state called
diapause
in insects—for the winter. The following spring, the ground would appear to boil as the nymphs hatched on warm days. Forming into immense aggregations or “bands” these immature locusts would march across the land, stripping the vegetation to fuel their development. The nymphs would molt five times, shedding their old outer cuticle and growing in size. On the final molt, the stubby wing buds were replaced with fully developed wings, the reproductive system was functional, and the adult locust was ready to swarm.

This next generation would typically continue the plague, riding the winds further into the heartland of the continent. After a buildup over the course of three or four years—and an equal number of generations—the outbreak would enter its final stage. Stretched to its southern and eastern limits, a portion of the population would stream
back to the Northwest in an apparent effort to return to its mountainous homeland. Scientists were unsure of whether this return migration was necessary to restock the founding population or whether a portion of the original population was always left behind in the Rockies to ensure the “seed bank” necessary to produce the next outbreak. In either case, they knew that the locust managed to sustain itself somewhere in the mountains, biding its time between irruptions.

The periodic outpouring of insect life from the West was intimately linked to weather, as Cline and the Weather Service suspected. The locusts flourished during droughts, which we can now infer to have provided several critical catalysts for population growth. The hot, dry weather weakened plant defenses and actually increased the nutritional value of the vegetation as sugars and other nutrients concentrated in the leaves. The dry conditions also suppressed fungal diseases, which could reach epidemic proportions and devastate locust populations in wet years. Furthermore, the heat accelerated the locusts’ maturation—and development was a race against predators that inflicted a constant mortality on the dense bands of nymphs. So, the faster the young locusts made it to adulthood, the greater the proportion of the population that would survive to reproduce. Finally, in times of drought lush vegetation was restricted to swales (and well-tended agricultural fields), so the locusts were forced to aggregate in these habitats, a behavior that initially generated and then sustained the coherence of both nymphal bands and adult swarms.

In the years immediately preceding Albert’s Swarm, a terrific drought had settled over the central United States. In 1873, just seven and a half inches of rain fell on Wallace, Kansas—the driest year on record. Dodge City experienced its third driest year in history in 1875. Missouri farmers reported that in 1874 “it stopped raining in April and didn’t rain again till late October.” The twelve months from May 1874 to April 1875 comprised the eighth driest period in 150 years of Ohio weather records. The heat and dryness were devastating for farmers and ideal for locusts.

Although drought conditions fostered population growth in the locusts, a second climatic factor was necessary to create a locust swarm of such incredible magnitude. There had to be a constant, southerly
wind to unite the insects over an immense area and maintain the coherence of the swarm for days on end during its northward migration. The monsoon weather that arises from the Gulf of Mexico might be suspected in this regard, but this meteorological event generally lacks essential elements of a June weather pattern. Not only does the monsoon typically develop later in the summer, but it also fails to sustain winds across a geographic scale necessary to propel a locust swarm from Texas to Minnesota. However, in the 1950s meteorologists discovered another annual event with the potential to have carried history’s greatest swarm: the Great Plains low-level jet.

This wind stream forms in late spring or early summer and extends into autumn. The 200-mile-wide flow of air is centered on Oklahoma and Kansas but stretches from the Gulf Coast to the Canadian border. This conveyor belt of air averages perhaps 10 miles per hour in the day and rises to 30 during the night—parameters that are consistent with those reported by Albert Child. The winds peak at about a thousand feet above the ground, again fitting with the scale of Child’s swarm. If no frontal systems move through the region, the Great Plains low-level jet blows for days on end. Furthermore, this wind system is strengthened by heat, as during a drought. Migrating birds are known to exploit this airstream in their northward journeys, and it seems nearly certain that the locusts did so as well.

So we can infer that the drought of 1874-1875 both fostered the buildup of locust populations and strengthened the jet that scientists call “one of the most prominent meteorological phenomena of the central United States.” Crowded into jittery populations spread across tens of thousands of square miles, the locusts almost certainly arose in separate swarms that were then coalesced by a wind stream that swept them into the perfect swarm.

By the 1870s, the nation was coming to realize that the Rocky Mountain locust was a tempestuous hurricane of insect life—that when these storm clouds shimmered on the horizon, a hail of hungry insects was coming. Although Albert’s Swarm was the greatest cyclone of locusts to sweep across the continent, Americans and Canadians had been painfully aware of this creature’s devastating capacity for some time.

Figure 2.1
An Introduction to Entomology
by William Kirby and William Spence, 1859

The first popular book of entomology to be published in English was an imposing series of five volumes beginning in 1815. By the time of the seventh edition in 1859, this comprehensive text had been mercifully reduced to a single volume that retained the luxuriant language and engaging prose of the earlier formulations. And the title was no less opulent (
Figure 2.1
).

In this definitive coverage of insect biology, William Kirby (sometimes called the Father of Entomology) and William Spence (a renowned beetle collector in his own right, but second fiddle to Kirby) had not yet learned of the locust outbreaks in the New World. However, they devoted a considerable portion of their book to these insects’ depredations in the Old World. They took pains to convince the reader that although a single locust was hardly intimidating, in the collective these creatures had rightfully earned their rapacious reputation:

These early British scientists were not duped by the extraordinary accounts of the ancient Romans, but they were convinced that the emanations of dead locusts could induce epidemics. They faithfully reported Saint Augustine’s assertion that rotting locusts had caused plagues that killed 800,000 people in the kingdom of Masanissa 2,000 years earlier and nearly a million in Italy in 591 C.E. Although heaps of decaying locusts are not a source of human disease, Kirby
and Spence’s accounts of famine are rather more convincing. They recounted the swarms that led to the deaths of 30,000 Venetians in 1478. To drive home the seriousness of locust plagues in their own time, they described how Yusuf Karamanli, the bashaw of Tripoli, raised a force of 4,000 soldiers to fight locusts (at about the same time that he was battling the U.S. Navy, which President Jefferson had sent in retaliation against the piracy that was humiliating his new nation and undermining its commerce). If the reader doubted Kirby and Spence’s implication that the gravity of a locust outbreak could justify mobilizing an army, so did some of the bashaw’s soldiers. But the authors explained that Karamanli was deadly serious about the situation “and very summarily ordered all to be hanged who, thinking it beneath them to waste their valour upon such pigmy foes, refused to join the party.”

 

Locust outbreaks have occurred on every inhabited continent. Europeans periodically suffered the invasions of several locust species into the last century, some of which were homegrown and others of which immigrated from Africa and Asia. However, modern pest management methods and conversion of natural habitats have largely ameliorated locust outbreaks in Europe. Africa, Asia, and Australia are still commonly plagued by various species of these insects, with outbreaks in Central Asia encompassing more than 6,000 square miles in 1999. Although the Australians have the most sophisticated locust management program in the world, the vast, uninhabited landscape makes finding and suppressing these outbreaks an immense challenge. South America is less frequently beset by locusts, but the grasslands of Argentina, Brazil, and Peru are prone to occasional infestations. Whereas parts of Mexico are sometimes overrun with a tropical locust related to those on other continents, the rest of North America hosted just a single, unique species of these insects, the Rocky Mountain locust.

The term
locust
is derived from the Latin,
locus ustus,
meaning “burnt place”—an allusion to the denuded landscape left in the wake of a ravenous swarm. If we think of life being sustained by oxidative metabolism, the slow burn of biochemistry, then perhaps associating
locusts with conflagrations is remarkably appropriate. In a very real sense, a swarm of locusts is a metabolic wildfire burning tons of vegetation every day to fuel its migration. The family to which all locusts belong, the Acrididae, may also derive its name from this sense of acrid corrosion that was associated with the damage caused by these insects.

Locusts were then—and still are—mysterious creatures, whose sudden irruptions are their defining attribute. In biological terms, a locust is a type of highly mobile grasshopper with the capacity to attain enormous population densities and a proclivity for aggregating and traveling in bands (as immature nymphs) and swarms (as winged adults). Aside from belonging to the family Acrididae, which has 10,000 species worldwide, the 10 species of locusts are not taxonomically related. The locust’s survival strategy has evolved within several subfamilies around the world, although only North America was blessed with just a single species of locust—along with several hundred species of grasshoppers.