Grasshopper Glacier in Custer National Forest
The Story of the Rocky Mountain Locust Buried in Ice
Feb 20, 2009
There is no doubt that it has been easier to hypothesize how so many of the grasshopper species Melanoplus spretus—commonly called Rocky Mountain Locust—became embedded in a glacier in southern Montana than why it became extinct. The Rocky Mountain Locust has not been seen in North America since 1902 and a plausible reason for its disappearance has only recently been uncovered.
A Quick Lesson About Grasshoppers Versus Locusts
The Rocky Mountain Locust is indeed a grasshopper, of the order Orthoptera, which includes grasshoppers, katydids and crickets. But there is some confusion about the use of the word “locust” because the scientific term varies from common usage. In general, a grasshopper becomes locust when it phases biologically to a migratory form that is larger, with longer wings, more powerful legs, and becomes more aggressive. Locusts express a tendency to swarm, whereas grasshoppers remain solitary.
Currently North America has no locusts. While there are grasshopper populations with the genetic capacity to express locust traits, those traits are not activated. Until conditions are right to trigger a change to the migratory form, they will remain grasshoppers. Summertime insects that buzz on hot afternoons and warm nights are typically katydids and cicadas, and are only called locusts in common language.
Locusts Used to Plague the Plains
The nation’s Great Plains used to be plagued by swarms of the destructive Rocky Mountain Locust as little as 135 years ago. This was a time of expansion, when settlers were setting up homesteads and farms in the open grasslands of places like Nebraska, Minnesota, Iowa and the Dakotas. The locust, which originated in the Rocky Mountains, swarmed the open prairies, devoured new crops and chewed anything and everything imaginable.
Professor Charles R. Bomar summarizes this in an educational case study at Sciencecases.org about the insect and its effect on American society. The locust caused widespread destruction and hardship that forced the government to provide relief for the devastated settlers. The locust plagues ended by the turn of the century and the insects disappeared, along with the prairie.
How Did Locusts Get in the Glacial Ice?
The Rocky Mountain Locust enjoyed a long life in the West before its 19th century disappearance. In 1953, scientist Ashley Gurney identified a specimen from the glacier that was carbon-dated to be up to 700 years old. According to the web site of Custer National Forest in Montana, it is believed that when large swarms of the Rocky Mountain Locust passed over the mountain range, they may have succumbed to the elements, which at that elevation can change quite suddenly in temperature and intensity.
Over time, snow and melting ice buried the insects, but glacial melting in the last 50 years has exposed the bodies—and evidence—to decomposition. Scientists needed to find and preserve Rocky Mountain Locust specimens in order to study them and determine what caused their demise. While Grasshopper Glacier in Montana is the most well-known spot where these insects are embedded in the ice, many other glaciers in the region hold frozen specimens, too.
What Caused the Locust’s Extinction?
University of Wyoming entomologist Jeffrey A. Lockwood published his research about the Rocky Mountain Locust in his 2004 book Locust: The Devastating Rise and Mysterious Disappearance of the Insect That Shaped the American Frontier. He describes his expeditions to various glaciers to find intact specimens of Melanoplus spretus; how the glaciers revealed a 300-year timeline of locust outbreaks; and his later conclusions about why the insect disappeared.
Lockwood suggests a number of factors contributed to the demise of the species in its permanent range in the Rockies. In short, the mountain valleys that provided the ideal conditions for the locust’s eggs to develop were populated by farmers and miners, who then over-plowed and over-irrigated, destroying the eggs and interrupting their life cycle. The locust’s original, small-scale, permanent home was lost to habitat destruction.
In the future it is possible that all the insects in Grasshopper Glacier, as well as the glacier itself, may be gone. The story of the relationship between westward expansion and the demise of the Rocky Mountain Locust offers a small lesson about the impact of environmental disruption.
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