Rocky Mountain Locust

Rocky Mountain Locust—The Rocky Mountain locust formed enormous swarms, possibly the largest known aggregations of any animal. (Phil Miller)

Rocky Mountain Locust—The Rocky Mountain locust formed enormous swarms, possibly the largest known aggregations of any animal. (Phil Miller)

The Rocky Mountain locust was small by typical locust standards, with an adult body length of 20 to 35 mm, long wings that extended past the end of the abdomen, and the enlarged back legs common to most grasshoppers. What this insect lacked in individual size it more than made up for in the size of its aggregations. Locusts, for much of the time, live their lives in the same way as most other grasshoppers—going about their business without being much of a nuisance to anyone—but occasionally, their populations may become very dense, and this triggers a dramatic change. The locusts change color, their wings grow, and they start to amass in swarms.

The swarms formed by the Rocky Mountain locust were incredible and probably represent some of the biggest aggregations of any land animal that has ever existed. A swarm observed in Nebraska during the summer of 1874 was of staggering proportions. Dr. A. L. Child of the U.S. Signal Corps was charged with assessing just how big this swarm was, and to get an idea, he measured the speed of the locusts as they were flying past and then telegraphed surrounding towns to get an idea of its extent. The swarm was estimated to be about 2,900 km long and 180 km wide. Observers in the Nebraskan towns over which this swarm passed reported that the gigantic cloud of insects obscured the sun and took five days to pass overhead. This begs the question of how many locusts there were in this enormous swarm. Estimates are as close as we'll ever get, but it has been calculated that there must have been around 12 trillion insects in this aggregation. All these fluttering insects weighed somewhere in the region of 27 million tonnes, and if the desert locust of the Old World is anything to go by, then this swarm may have eaten its own weight in food every day just to sustain itself. Luckily, the Rocky Mountain locust was not a fussy eater—it would nibble a huge range of plants, and in the absence of foliage, it would munch bark, leather, laundry, dead animals, and even the wool off a sheep's back. As can be imagined, the multitude of mandibles left a trail of devastation, and between 1873 and 1877, the vast swarms of insects caused massive crop damage in Nebraska, Colorado, and some other states, estimated at around $200 million.

Around 30 years after these immense swarms left a trail of devastation in their wake, the Rocky Mountain locust mysteriously vanished. The reason behind the extinction of this insect has been speculated on for some time. Some experts have suggested that the species never became extinct and that the locust was actually the swarming phase of a species that can still be found today, a theory that has been shown to be incorrect. The likely explanation for the disappearance of this insect is that outside of its swarming periods, the locust retreated to the sheltered valleys of Wyoming and Montana, where the females laid their eggs in the fertile soil. These very same valleys attracted the attention of settlers, who saw their potential for agricultural endeavors, and with their horses and their plows, they turned the soil over and grazed their livestock on the nutritious grass. These actions destroyed the eggs and developing young of the insect, and around three decades after its swarms blotted out the sun, the Rocky Mountain locust was gone forever.

♦ The swarming of grasshopper species, such as the Rocky Mountain locust, is thought to be a survival mechanism that allows the insects to disperse into new habitats when things get a little cramped during periods of worsening environmental conditions that concentrate the nymphs into ever shrinking areas. In their normal or solitary phase, the grasshoppers are very sensitive to the presence and proximity of others of their kind. When things start to get a bit too cozy, the insects switch from intolerance to attraction, forming so-called bands of nymphs. The locusts take on the appearance of the swarming insect and fly off in search of more space and food.

♦ Settlers in the native range of the locust also killed huge numbers of beavers and widened streambeds, both of which led to increased flooding and the death of locust eggs and young in the ground. These settlers also planted alfalfa over huge swathes of ground, a plant that the locust was not fond of eating. It has also been suggested that bird species from the eastern United States followed the settlers along corridors of cot-tonwood, preying on huge numbers of insects, including the locust.

♦ Female Rocky Mountain locusts used a pair of tough valves at end of their abdomens to excavate a tunnel and deposit their eggs below the surface of the soil, where they would be out of the sight of most predators. For added protection, the eggs were co-cooned in a hardened foam egg sac with the appearance of a stale marshmallow.

♦ Some of the glaciers of the Rocky Mountains are known as grasshopper glaciers as large numbers of Rocky Mountain locusts from the swarms were driven by winds high up into the mountains, where they perished on the glaciers, only to be covered by subsequent layers of snow and ice. As these glaciers thaw, they reveal the mummified remains of these insects.

♦ Although the Rocky Mountain locust was very numerous, surprisingly few specimens are to be found in collections. Entomologists at the time saw little point in collecting such numerous animals, as it was inconceivable to them that an insect forming such vast swarms could ever become extinct.

Further Reading: Chapco, W., and G. Litzenberger. "A DNA Investigation into the Mysterious Disappearance of the Rocky Mountain Grasshopper, Mega-Pest of the 1800s." Molecular Phylogenetics and Evolution 30 (2004): 810-14; Samways, M. J., and J. A. Lockwood. "Orthoptera Conservation: Pests and Paradoxes." Journal of Insect Conservation 2 (1998): 143-49; Lockwood, J. A., and L. D. DeBrey. "A Solution for the Sudden and Unexplained Extinction of the Rocky Mountain Grasshopper (Orthoptera: Acrididae)." Environmental Entomology 19 (1990): 1194-1205; Lockwood, J. A. "Voices from the Past: What We Can Learn from the Rocky Mountain Locust." American Entomologist 47 (2001): 208-15; Lockwood, J. A. Locust: The Devastating Rise and Mysterious Disappearance of the Insect That Shaped the American Frontier. New York: Basic Books, 2004.

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  • estella zaragamba
    Why rocky mountain locust disappeared?
    7 years ago

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