The Locust that Ate the American West

The Rocky Mountain locust was a force to be reckoned with.
The Rocky Mountain locust was a force to be reckoned with. / Julius Bien, Wikimedia Commons // Public Domain (Rocky Mountain locust illustration); Pobytov/Getty Images (background painting)

On a hot summer’s day in 1875, an 8-year-old girl stood outside her family’s southwestern Minnesota farm and stared up at the sky. A strange, cloud-like mass swept over the sun, glinting and glimmering in the dim light. The girl was riveted—until she felt something make impact with her head and hit the ground.

In the dry dirt at her feet was an enormous brown grasshopper, the largest she’d ever seen. And before she could fully take it in, the insects began to thud to the ground all around her like rain.

That girl was a young Laura Ingalls Wilder, and the future Little House on the Prairie writer had no idea that all across the central United States, farmers were spotting the same indescribable cloud. One likened it to an impending thunderstorm; another compared the noise to a distant threshing machine. None of them realized that the 1875 swarm of locusts would be the largest ever seen in North America—or that before the insects vanished from the face of the continent, they would leave a swath of destruction and devastation in their wake. 

Grasshopper Weather

Locusts start out as innocent brown or green grasshoppers, living solitary lives in arid regions. And most of the time, that's where their story ends. But during a period of rain following a long drought, the grasshopper population explodes—and for reasons still not fully understood, the proximity spurs some species of the insect to molt into brightly colored, long-winged, ravenous locusts that band together into a terrifying swarm

The Rocky Mountain locust (Melanoplus spretus, spretus meaning “despised”) was the most feared in North America. There were so many of them that their biomass (the total weight of a species in a set habitat) was equivalent to that of their much-larger prairie neighbors, the American Bison, during the 19th century. The locusts thrived in drought conditions; warmer temperatures kept fungal infections at bay, concentrated precious sugars in heat-shriveled plants—and made the insects mature faster. Seasons of hot, dry weather were a locust time bomb.  

In 1873, a severe El Niño event caused a dry summer and hot autumn, weather that carried the ominous western moniker “grasshopper weather.” A swarm of Rocky Mountain locusts touched down in southwest Minnesota, just one year before the Ingalls family arrived at Plum Creek in 1874. But the worst was yet to come.

In 1874, the insects covered the skies between Texas and the Dakota Territory. They hitched a ride on the Great Plains low-level jet, an air current stretching from Texas to Saskatchewan that only grew stronger in the dry heat.  With each swarm, the locusts planted eggs by the millions. And so the insects’ number grew and grew, inching toward a cataclysmic event that came to be known as Albert’s Swarm, after the man who calculated its staggering size. 

The Swarm of a Century

An 1877 illustration of female Rocky Mountain Locusts laying eggs.
An 1877 illustration of female Rocky Mountain locusts laying eggs. / Charles Valentine Riley, Wikimedia Commons // Public Domain

Albert Lyman Child was a meteorologist based in Nebraska. From June 10 to 25, 1875, he used a telegraph to collect data on a locust swarm for the U.S. Signal Corps and determined that that year's swarm appeared to be 110 miles wide and 1800 miles long, far bigger than anything seen before. When he tried using a telescope to determine its height, he noted, “It seemed like piercing the milky-way of the heavens; my glass found no limits to them. They might have been a mile or more in depth.” 

Child estimated the swarm covered 198,000 square miles, only slightly smaller than Colorado and Wyoming combined. The cloud contained about 3.5 trillion locusts.

The insects are notoriously voracious eaters. (According to the World Bank, a “small swarm” of just 80 million desert locusts—which can be found in Africa, Asia, and the Middle East—is capable of eating as much food as 35,000 people each day.) When the trillions of ravenous Rocky Mountain locusts touched down in the American West, they devoured everything in sight. Young Laura Ingalls watched as her family’s prize wheat crop, their path out of poverty, was consumed. Other farmers observed in shock as the insects ate their fence posts, the handles of their tools, the wool off their sheep, even the clothes off their backs. When there was nothing left, the locusts ate each other.  

The Ingalls family, like many other farmers, lit fires around their wheat field only to discover the locusts remained undeterred by the smoke. Prairie women covered their gardens with sacks and blankets; the insects merely ate the fabric. Some farmers tried “hopperdozers,” a sheet metal contraption that horses pulled across fields like a plow, or a similar vacuum-style invention. They caught some insects, but were overwhelmed by the sheer number of locusts. Angry at their own helplessness, the most desperate dynamited the land in an attempt to kill the eggs. 

The Rocky Mountain locust caused more than $200 million in damage to western agriculture in the 1870s [PDF], equivalent to over $100 billion today. Many farms never recovered from the devastation.

A Quiet Disappearance 

To the country’s relief, the locust's natural cycle of boom and bust turned in the settlers' favor, and the insects' populations declined after the 1870s. It appeared that the Rocky Mountain locust had returned to life as a humble grasshopper, waiting until the next drought to strike again.

When a small swarm appeared in Manitoba, Canada, in 1902, it was assumed to be part of the usual cycle. Instead, it was their last appearance. The Rocky Mountain locust quietly vanished.  

It took entomologists about a decade to notice the absence of the locusts, and the issue didn't receive much attention during the World Wars and the Great Depression. It wasn’t until the late 20th century that a theory for their disappearance was proposed. 

It all came down to the species's typical choice of habitat for reproduction. While the Rocky Mountain locusts laid their eggs on the prairie during a swarm, they retreated to lakes and river valleys in the Rocky Mountains during their normal mating seasons. Unfortunately for the locust, those areas were ideal farmland for U.S. settlers out West, and cattle hooves and plows destroyed the land where the species laid their eggs. "By converting these valleys into farms—diverting streams for irrigation, allowing cattle and sheep to graze in riparian areas, and eliminating beavers and their troublesome dams—the pioneers unknowingly wiped out locust sanctuaries," author and entomologist Jeffrey A. Lockwood wrote for High Country News in 2003.

This theory has been accepted by many entomologists, but not everyone is convinced the Rocky Mountain locust is truly extinct. Dr. Dan Otte, a senior curator at the Academy of Natural Sciences, told Discover in 2003 that it’s possible they’re hanging around undetected, simply mistaken for another species. The Rocky Mountain locust may still exist in remote pockets of North America, waiting for the day it can once again block out the sun.