Montana Headwall » Wild Things

Swarm on ice

How history froze on Grasshopper Glacier



The dark cloud would have appeared normal at first, an afternoon storm building over the Beartooth Range. However, there was something different about the cloud’s texture, and, moments later, its sound. Storm clouds shroud mountains like a thick gray soup. The sounds associated with them are wind and thunder. This cloud pixelated the atmosphere and hummed.

As the din swelled, it was clear this was no cumulonimbus weather event, but rather a swarm of locusts. Then, just as the flying mass reached the eastern slopes of the Beartooths, it stopped, swatted from the sky by ... the weather.

Montana Headwall
  • Jeffrey Lockwood

In a case of disrupted migration, a storm blindsided the cold-blooded locusts and knocked them onto a glacier at 11,300 feet above sea level on the north side of Iceberg Peak. Subsequent blizzards buried the bugs for hundreds, perhaps thousands of years, but they resurfaced a century ago as the ice sheet, now fittingly called Grasshopper Glacier, receded.

J.P. Kimball, a geologist looking for mining opportunities, discovered the frozen insects in the early 1900s. Shortly afterward, the U.S. Bureau of Entomology determined them to be extinct Rocky Mountain locusts (Melanoplus spretus).

Just 30 years prior to Kimball’s discovery, trillions of Rocky Mountain locusts still inhabited the western United States. Scientists estimate that locust outbreaks used to occur in Montana about twice each decade. According to Jeffrey Lockwood, a professor of Natural Sciences and Humanities at the University of Wyoming who has studied Rocky Mountain locusts much of his career, swarms like those entombed in Grasshopper Glacier were part of the species’ lifecycle.

“Locusts sense crowding, by touch and smell, as an indication that food sources will be in short supply in the near future,” Lockwood says. “It triggers morphological changes. They grow longer wings because they have to get the hell outta there. Their color changes, perhaps to fool predators into thinking they taste nasty, and their reproduction is suppressed in exchange for building energy reserves.”

Lockwood believes the change from content hopper to pandemic pestilence is a survival mechanism.

“When they’re not crowded, locusts tend to avoid each other, but as they change from solitary to migratory, they seek close contact, like schooling fish,” he says. “With 100 million in a swarm, the chance any one of them will be bird food is low.”

Montana Headwall
  • Jeffrey Lockwood

Historically, some locust outbreaks were so dense they created multiday solar eclipses. They devoured plants, laundry, leather, even the wool off the backs of sheep, but the locusts that swarmed the Beartooths made either a navigational error or flew into a freak storm and froze to death.

Grasshopper Glacier on Iceberg Peak is one of at least three locust-encrusted ice sheets in Montana. A second in the Beartooths is called Hopper Glacier, and the third, another Grasshopper Glacier, is in the Crazy Mountains. In the 1990s, Lockwood discovered yet another in Wyoming’s Wind River Range.

The one on Iceberg Peak is the best known, and it’s disappearing. Years of diminishing snowfall and melting have reduced it from over five miles to less than a quarter-mile across. For many years, anyone could make the four-mile hike to Grasshopper Glacier and chip out a perfectly preserved hopper. Recently, more and more of the locusts have melted out of their icy tomb and decomposed.

How could a species numbering in the trillions disappear so quickly at the end of the 19th century? Between outbreaks, the locusts lived in river valleys, the same places pioneers found best for agriculture. Those early farmers unknowingly wiped out the locusts when they diverted streams for irrigation, allowed cattle and sheep to graze riparian areas, and eliminated beavers and their dams.

Now, the only evidence of their existence—the ones encrusted in Rocky Mountain ice—are on the verge of disappearing as well.

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