Locust by Jeffrey A. Lockwood Read Free Book Online Page B

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