Rocky Mountain Locust

Record: A swarm of 12.5 trillion locusts

The correct biological term for animals that form large groups is “swarm,” but when it comes to large assemblies of migratory locusts, the term “plague” is used because they not only migrate but also devastate entire regions. Migratory locusts differ from ordinary grasshoppers in their destructive behavior: their populations grow rapidly, and they consume all vegetation in a region before moving en masse to the next food source. The most infamous migratory locust to plague North America was the Rocky Mountain locust, also known as the Rocky Mountain grasshopper.

The Locust Plague of 1874

One of the most devastating locust plagues occurred in the summer of 1874, when vast swarms of Rocky Mountain locusts swept across the Great Plains in the U.S. and Canada. This plague covered 5.2 million square kilometers and destroyed crops in multiple states, including Iowa, Minnesota, Nebraska, Kansas, and Texas. The number of locusts was estimated at up to 12.5 trillion, and the economic damage amounted to millions of dollars. In some areas, the swarms were so dense that they darkened the sun for hours. American author Laura Ingalls Wilder described the event in her autobiographical children’s book On the Banks of Plum Creek (1937):

“The Cloud was hailing grasshoppers. The cloud was grasshoppers. Their bodies hid the sun and made darkness. Their thin, large wings gleamed and glittered. The rasping whirring of their wings filled the whole air and they hit the ground and the house with the noise of a hailstorm.”

On the Banks of Plum Creek. 1937. L. Ingalls Wilder

The locusts devoured everything in their path: fruits, trees, clothing, wooden beams, leather, even wool from sheep – and occasionally each other. Their remains contaminated water sources, and trains were immobilized as they slid over tracks made slippery by the insects. Farmers’ attempts to combat the locusts with fire and explosives failed. Other methods, such as covering fields with tarps or drowning the insects in water and oil-filled ditches, also proved largely ineffective. A device called the “Hopperdozer” was designed to trap locusts using tar, but it only worked on flat fields.

Eat or be eaten: Locusts as food?

In 1875, Charles Valentine Riley, an entomologist from Missouri, proposed in The Rocky Mountain Locust that locusts could be used as a food source to both reduce their numbers and feed hungry settlers. He noted that humans and animals had consumed locusts since ancient times. According to Riley, locusts fried in butter had a nutty flavor and could even make a tasty soup. Some settlers tried Riley’s recipes, finding the locusts comparable to crayfish in taste. However, many farmers, devastated by the plague, refused to eat the insects.

A 2022 archaeological discovery in Crypt Cave near Winnemucca Lake, Nevada, suggests that locusts were indeed a food source for early North American cultures. In a pit, about 1,000 Rocky Mountain locust remains were uncovered, dating back approximately 14,100 years. This pit, measuring 60 to 80 centimeters deep, was likely used to store large quantities of locusts, which the region’s inhabitants collected and consumed.

The grasshopper plague struck the region during a record-breaking drought, exacerbating the already dire situation. In the hardest-hit areas, food shortages became so severe that U.S. President Ulysses S. Grant ordered the distribution of army supplies in November 1874. Despite initial hesitation, both the federal government and private organizations provided aid in the form of food, clothing, and seeds. In 1875, residency requirements for affected farmers were relaxed, allowing them to temporarily leave their farms to seek assistance.

Albert’s swarm in 1875

The continuation of the 1874 locust plague, or part of the larger locust infestations of the 1870s in North America, is known as “Albert’s Swarm.” This term refers to the migratory locusts that traveled through the western U.S. in 1875, particularly affecting Missouri and Nebraska. The event was named after Dr. Albert Child, who estimated the swarm’s size at 510,000 square kilometers by multiplying its estimated speed with the time it took to pass through southern Nebraska.

The Rocky Mountain locust plague lasted several years. A combination of an early frost and the destruction of locust eggs through field plowing in 1875 eventually led to a decline in their numbers. While entomologist Jeffrey A. Lockwood, in his book Locust: The Devastating Rise and Mysterious Disappearance of the Insect that Shaped the American Frontier (2004), estimated the number of locusts in the swarm at 3.5 trillion, other sources suggest as many as 12.5 trillion – making it, according to the Guinness Book of World Records, the largest concentration of animals ever speculated.

Rocky Mountain locust – Fact sheet

Alternative name	Rocky Mountain grasshopper
Scientific name	Melanoplus spretus, Calopentus spretus, Acridium spretis, Pezotettix spretus
Original range	North America (Canada and USA)
Time of extinction	1902
Causes of extinction	destruction of breeding areas, loss of habitat, persecution by humans
IUCN status	extinct

Locust plagues documented since the 18th century

The Rocky Mountain locust caused significant damage in North America long before the infamous plague of 1874. According to an article by Chuck Lyons, there are records of locust plagues dating back to the 18th century. Between 1743 and 1756, Rocky Mountain locusts devastated crops on farms in Maine, and between 1797 and 1798, farms in Vermont were similarly affected.

In the 19th century, these plagues became increasingly threatening as agriculture expanded westward into the preferred habitats of the locusts. From 1828 to 1855, there were several plagues that impacted large parts of the western U.S. Minnesota, in particular, experienced several outbreaks between 1856 and 1865, while Nebraska was hit seven times by locust swarms between 1856 and 1874. Although these plagues caused significant regional damage, they were relatively contained.

The most devastating plague occurred between 1873 and 1877. During the hot summer months, the locusts hatched along the eastern slopes of the Rocky Mountains and, in massive swarms, spread out in search of food, invading the fertile lands of the Great Plains. The plague covered a vast area, affecting not just one but several states. The hardest-hit regions were Kansas, Nebraska, the Dakota Territory, Iowa, Missouri, and Minnesota.

Farmers were ill-prepared for such plagues. Many were already struggling with the economic downturn caused by the 1873 financial crisis and the drought of 1874. The locust plague destroyed their crops, forcing many to abandon their farms and return east. In Kansas, up to a third of the population was displaced by the catastrophe.

To combat the plagues, Nebraska passed a law in 1877 requiring all citizens between the ages of 16 and 60 to spend at least two days actively fighting the locusts, particularly during the hatching season. Those who refused faced a $10 fine. At the same time, Missouri introduced a bounty program, paying $1 per bushel of locusts collected in March, with the bounty gradually decreasing over the following months. Other Great Plains states implemented similar measures to motivate people to fight the devastating plagues.

By the 1880s, farmers had recovered from the locust plagues. One of the most successful adaptations was the shift to more resilient crops, such as winter wheat, which matured earlier and was thus less vulnerable to locust infestations. These changes helped farmers better prepare for future plagues and minimize crop losses, though they likely had a devastating effect on the Rocky Mountain locust population.

Rocky Mountain locust: Taxonomy and characteristics

The British-American entomologist Benjamin Dann Walsh first introduced the scientific name Caloptenus spretus for the Rocky Mountain locust in his 1866 work Grasshoppers and Locusts. The species had originally been named by Philipp Reese Uhler, though without a formal description. Walsh explained that “the name ‘spretus’ means ‘despised’, and refers apparently to its having been hitherto despised or overlooked by entomologists.” However, Walsh did not provide a detailed description of the species and only briefly touched upon its biology, ecology, and control.

In 1878, American insect researcher and paleontologist Samuel Hubbard Scudder clarified in an essay that the Rocky Mountain locust belonged to the genus Melanoplus, not Calliptenus as Walsh had mistakenly believed (Walsh referred to it as Caloptenus, now known as Calliptamus). Melanoplus species are predominantly found in North America, while Calliptamus is native to Europe, North Africa, and Asia. The behavior of the Rocky Mountain locust, especially its long migrations through dry, open areas like prairies and deserts, also aligned more closely with other Melanoplus species.

The Rocky Mountain locust, which grew to a length of 2 to 3.5 centimeters, was well adapted to the harsh conditions of the North American prairies and mountain regions. With powerful hind legs, it could leap great distances, while its robust body and short but functional wings were optimized for swarm behavior. Typical of the Melanoplus genus, the Rocky Mountain locust had well-developed mandibles, allowing it to consume large amounts of plant material in a short time.

A quote from Branden Holmes in What’s Lost and What Remains encapsulates the contemporary attitude toward the species:

“Like those extinct species known only from a few specimens, the trillion strong global population yielded little hard data because it was considered a pest species. There was simply no interest in trying to understand the species, only in eradicating it.”

What’s Lost and What Remains: The Sixth Extinction in 100 Accounts. 2021. p. 184. B. Holmes.

Discovery of Rocky Mountain locust remains

Entomologist Jeffrey Lockwood from Wyoming, along with his students, embarked on a search for remains of the Rocky Mountain locust, which had been preserved in the so-called “Grasshopper Glaciers” along the Rocky Mountains. Lockwood shared his findings in a 2003 article for High Country News. After several unsuccessful attempts, they finally uncovered intact remains on the Knife Point Glacier in Wyoming’s Wind River Mountains. These remains were radiocarbon-dated to the early 17th century, likely after a swarm of locusts had been immobilized by the cold and subsequently trapped in the glacier.

Lockwood and his team discovered around 130 well-preserved specimens, which had resurfaced as the glacier melted. These findings provided valuable insight into the extinction of the Rocky Mountain locust. The specimens were carefully collected, cataloged, and preserved for further study, offering new perspectives on the life and sudden decline of this once-abundant species.

What are locusts?

Locusts, from the family Acrididae, exhibit destructive and migratory behaviors typical of “plagues.” However, not all grasshoppers are constantly migratory; this behavior is a specific response seen in certain species when triggered by environmental conditions. Typically, these locusts live as solitary individuals in the solitary phase. However, when populations surge or food becomes scarce, they shift into the gregarious or swarming phase. This transition is triggered by the hormone serotonin.

In the gregarious phase, locusts form large swarms, alter their physiology, and travel long distances in search of new food sources. Species such as the Rocky Mountain locust and the desert locust (Schistocerca gregaria) possess this ability, while other grasshopper species do not display such behavior.

During this phase, locusts not only change their behavior but also their appearance: their colors become more vibrant, they may grow larger and more robust to better compete in swarms, and they often develop longer wings, enabling them to fly great distances in large groups, further increasing their efficiency as a swarm.

Range of the Rocky Mountain locust

The Rocky Mountain locust was native to vast regions of North America, particularly along the Rocky Mountains and the prairies. Its preferred habitat was the dry, sandy areas of the Rocky Mountains, where it also bred. However, in swarm years, massive migrations occurred, with the locusts covering large parts of the Great Plains and the Midwest. These swarms could stretch from Canada to Mexico and from Utah to Iowa.

Typically, the locusts remained in their breeding grounds, which included river valleys and floodplains of the Rocky Mountains. However, when their population surged, often triggered by droughts, the swarms would migrate to more fertile areas such as the prairies in search of food. This high mobility and the ability to migrate en masse greatly expanded their range, contributing to the devastating locust plagues of the 19th century.

In his Revision of the Orthopteran Group Melanopli Acridiidae (1898), Scudder notes that the Rocky Mountain locust descended from the Rockies into the prairies only in specific years, particularly during dry seasons, following western wind currents. The plagues typically lasted for two consecutive years.

Reasons for the extinction of the Rocky Mountain locust remain unclear

The Rocky Mountain locust, once one of the most common grasshopper species in North America, mysteriously disappeared within just 20 years. According to the International Union for Conservation of Nature (IUCN), the last known specimen was collected in 1902 in Aweme, near Brandon, Manitoba. Between 1850 and 1880, the species reached immense population sizes across the prairie regions, before its numbers abruptly collapsed, never to recover.

Jeffrey Lockwood and Larry D. Debrey described the locust’s extinction as possibly the only documented case of a pest species going extinct in agricultural history. In their 1990 study A Solution for the Sudden and Unexplained Extinction of the Rocky Mountain Grasshopper, they explored various theories about the sudden disappearance of the locust. They dismissed most previous speculations, concluding that large-scale changes in the western U.S., such as climatic shifts or the decline of Indigenous populations and bison, were not likely the main causes. With the locust population already in sharp decline by the early 1880s, even small environmental changes may have triggered its final extinction.

The decline of Indigenous peoples, bison, and beavers

It is believed that the Rocky Mountain locust was heavily dependent on the plants of the tallgrass prairie during periods of drought. This prairie ecosystem, with its deep-rooted plants, provided stable soil and crucial food sources that were essential for the insects’ survival during dry spells. Natural fires, as well as those set by Indigenous peoples, played a significant role in maintaining the prairie by preventing the encroachment of trees, recycling nutrients into the soil, and promoting seed germination. For the locusts, these periodic disturbances created an open landscape with the resources necessary for their reproduction and survival.

The decline of bison populations may have further impacted the survival of the Rocky Mountain locust. Bison played a key role in keeping the grasslands open by grazing, which prevented the growth of trees and shrubs. This grazing created ideal breeding and feeding grounds for the locusts. Additionally, bison contributed to soil nutrient cycles and helped disperse plant seeds. As bison disappeared, the grasslands became denser and less suitable for locust breeding, making their reproduction more difficult.

The loss of beavers likely also contributed to the locust’s extinction. Beavers created wetlands and river valleys through dam-building, which were vital habitats for many species, including the locust. These wetlands provided stable conditions for locust egg-laying and nymph development. The sharp decline in beaver populations in the 19th century, driven by intense fur trading, led to the disappearance of these wetlands. With them, critical habitats for the locust vanished, accelerating their decline.

Destroyed egg-laying sites prevented reproduction

Lockwood and Debrey largely attribute the extinction of the Rocky Mountain locust to the destruction of its egg-laying and development sites. The most affected areas were the river valleys, which were the locust’s preferred habitats, lost due to human expansion and agricultural development. These disruptions hit the locust population at a time when it was already naturally declining. Plowing and irrigating farmland, particularly along the Mississippi, likely disrupted the locust’s lifecycle. Female locusts used the fields for egg-laying, but plowing destroyed the eggs, hindering reproduction.

Additionally, the introduction of livestock, new plant species, and the spread of birds worsened the destruction of their habitat in the late 1880s. In Locust: The Devastating Rise and Mysterious Disappearance of the Insect that Shaped the American Frontier (2004), Jeffrey Lockwood noted that farmers reportedly destroyed up to 150 locust egg beds per 6.45 square centimeters while plowing, harrowing, or flooding their fields.

Abandonment of original breeding grounds

In 1878, American entomologist Cyrus Thomas observed in On the Orthoptera collected by Dr. Elliott Coues, U.S.A., in Dakota and Montana, during 1873-74 that Rocky Mountain locusts were only present in the prairies during swarm years, where they also reproduced. As the swarms ventured farther from their native habitats in the Rocky Mountains, the population decreased with each generation. This suggests that the locusts struggled to thrive and reproduce outside their natural breeding grounds in the prairies.

According to Jeffrey Lockwood (2004), the primary breeding grounds for the Rocky Mountain locust were located in sandy soils near rivers and streams in the Rocky Mountains. These core habitats provided ideal conditions for reproduction under normal circumstances. However, as settlers expanded agricultural activity, these breeding grounds overlapped with farmland, leading to the destruction of locust egg beds, which likely contributed significantly to the species’ decline.

Samuel Hubbard Scudder also speculated in 1898 that although large numbers of eggs were laid in the prairies during locust swarms, the resulting offspring were generally not viable. He attributed this to the species’ poor adaptation to prairie habitats, which greatly diminished their survival chances outside their native breeding areas.

Lack of genetic diversity?

Another hypothesis regarding the extinction of the Rocky Mountain locust involves genetic diversity. In 2004, entomologists William Chapco and Greg Litzenberger conducted a molecular phylogenetic study, analyzing mitochondrial DNA from five locust specimens preserved in museums, as well as fragments found in 400-year-old glacial deposits in Wyoming. Their findings revealed that the genetic diversity of the analyzed specimens fell within the known range for other species of the Melanoplus genus. This contradicts the theory that a genetic bottleneck, a sharp reduction in genetic variability, contributed to the locust’s extinction.

Despite the Rocky Mountain locust exhibiting considerable genetic diversity, it still failed to adapt to the environmental changes caused by human settlement and agricultural expansion. The main reason for the species’ extinction remains unclear, though habitat destruction due to human activity is considered the most likely cause. The IUCN, which officially declared the locust extinct in 2014, supports Lockwood and Debrey’s theory that the destruction of its breeding habitats was a key factor in the species’ disappearance.

Could the Rocky Mountain locust have survived?

After Jeffrey Lockwood discovered frozen remains of the Rocky Mountain locust in glaciers during the 1990s, he embarked on several expeditions to remote river valleys near Yellowstone National Park, hoping to find living specimens. These regions, untouched by agriculture, were considered possible refuges for the locust. Despite intensive efforts, the search proved unsuccessful, and no live locusts were found.

In 2002, Daniel Otte, a South African-born American expert on grasshoppers and crickets, suggested that the Rocky Mountain locust might not be extinct but merely dormant, waiting for favorable conditions to emerge again. There are examples of insects that survive long periods in secluded areas during non-outbreak periods. Cicadas, for instance, are known to live underground for years, reappearing only when high temperatures and dense vegetation trigger their emergence. Such insects can go undetected for generations, sometimes being presumed extinct, as was the case with the cicada species Okanagana arctostaphylae, rediscovered in 2024 after 100 years.

Since locusts in their migratory phase look different from their normal solitary phase, some speculated that the Rocky Mountain locust might not be extinct after all. For example, entomologist John Capinera, in Grasshoppers of Colorado (1982), suggested that the Rocky Mountain locust could have been a migratory phase of the still-existing species Melanoplus sanguinipes, living on under this new identity.

Some entomologists even attempted to induce swarming behavior in Melanoplus sanguinipes by artificially creating high-density conditions. These experiments, however, failed to recreate the massive swarms, disproving the theory that the Rocky Mountain locust could be “reawakened” through a phase transformation.

The results of a 2004 study by Chapco and Litzenberger confirmed that the Rocky Mountain locust was a distinct species and not merely a migratory form of any extant species. It differs significantly from other short-horned grasshoppers (Caelifera), confirming that it is indeed extinct. Moreover, their findings suggested that the species is correctly classified within the Melanoplus genus, and surprisingly, its closest living relative is likely Melanoplus bruneri, a Mexican grasshopper species, rather than M. sanguinipes as previously thought.

Lessons from the history of the Rocky Mountain locust

In his essay Voices from the Past: What Can We Learn from the Rocky Mountain Locust (2001), Jeffrey Lockwood offers valuable insights into the lessons we can draw from the extinction of the Rocky Mountain locust, particularly regarding environmental awareness and the unintended consequences of human actions on nature.

One of the key takeaways is that even a massive population size is no guarantee for a species’ survival. Despite the Rocky Mountain locust’s vast swarms, which devastated entire regions, the species disappeared within a few decades. Lockwood highlights that even widely distributed species can go extinct if their habitats are destroyed through human activities.

Another crucial point is the unintended consequences of human intervention. The extinction of the locust was likely an unintended result of settlement and agricultural expansion, particularly the destruction of its breeding grounds in river valleys. Lockwood emphasizes that human actions, even when not consciously harmful, can have profound and far-reaching environmental impacts.

The loss of the Rocky Mountain locust serves as a cautionary tale of how quickly species can vanish irreversibly. The long-term ecological consequences remain unclear, but some experts, including the U.S. Fish & Wildlife Service (2006), suggest a link between the locust’s extinction and the decline of the Eskimo curlew (Numenius borealis). This bird, last recorded in 1939, relied on locusts as a food source during its spring migration. The disappearance of the locust may have further pressured already dwindling curlew populations, alongside factors such as hunting and the conversion of grasslands into farmland.

Lockwood also underscores the importance of protected habitats. He shows that species, even those with large populations, often depend on specific environments for survival. Protecting these areas is essential for conserving biodiversity. Lastly, Lockwood warns against viewing nature purely through an economic lens. The Rocky Mountain locust was primarily seen as a pest, with its ecological role overlooked. This narrow, economic perspective meant that the loss of the species was only recognized too late, when its extinction was already irreversible.

Parallels between the Rocky Mountain grasshopper and the passenger pigeon

The lessons formulated by Jeffrey Lockwood can be almost seamlessly applied to the story of the passenger pigeon (Ectopistes migratorius), which was once considered the most abundant bird species in the world. Both species formed massive swarms so large that they darkened the sky. Reports from the 19th century describe locust swarms that blocked out the sun for hours – similar to the passenger pigeon flocks, which also obscured the sky and were visible for days. Both the Rocky Mountain locust swarms and the passenger pigeon flocks caused devastating damage in North America, consuming entire fields.

Both species went extinct in the early 20th century, despite once being so numerous that their extinction seemed unimaginable. The Rocky Mountain locust and the passenger pigeon were heavily targeted due to the agricultural damage they caused, which ultimately contributed to their demise. In both cases, it becomes clear that human intervention, coupled with habitat changes, led to the extinction of these once-abundant species.