What Caused the Las Vegas Grasshopper Invasion? Can It Happen Again?

The historic 2019 swarm was attributed to rain levels in Southern Nevada

Las Vegas grasshopper invasion
Massive swarms of grasshoppers descend on the Las Vegas Strip, passing through town on their northbound migration. BRIDGET BENNETT/AFP/Getty Images

In July of 2019, the city of Las Vegas was invaded by a massive swarm of grasshoppers so large, it could be detected by weather radar. While it may have looked like something out of an apocalyptic horror film, the massive grasshopper swarm was actually attributed to unusual weather patterns in southern Nevada.

Weeks prior to the grasshopper invasion, Las Vegas had seen 4.63 inches of rain, almost twice its normal average of 2.38 inches in the same period. With the climate crisis expected to create more frequent extreme weather events, episodes like the grasshopper swarms in Las Vegas are also likely to occur.

Grasshopper Migration

While certainly unusual (and perhaps a bit unsettling), scientists assured the public that this particular species of grasshopper was completely harmless. The common species of pallid-winged grasshoppers was native to the deserts of western North America, and were just following their typical migration patterns after wet winters or springs. In 2019, the extreme rainfall had simply pushed them farther north than normal. The Las Vegas Review-Journal reported that high wind gusts in the valley from the previous night may have forced the swarm into higher altitudes, as well.

Massive swarms of locusts threaten agriculture and food supply across East Africa, Asia, and the Middle East, devastating crops and affecting the livelihoods of local communities. While swarms typically occupy around 100 square kilometers, a 2020 swarm in Kenya was recorded spanning 2,400 square kilometers (927 square miles) — over three times the size of New York City. At typical sizes, a locust swarm contains between 4 billion and 8 billion individuals and can consume the same amount of food that 3.5 million people would normally eat in a day. So, it's not surprising that a large number of grasshoppers would cause a bit of alarm here in the United States.

Locusts are a part of the grasshopper family, but with some pretty notable differences. All species of locusts undergo a neurochemical transformation when they join larger groups of the same species, shifting to what scientists call that gregarious phase, resulting in a swarm mentality. The process makes them stronger and results in their ability to fly greater distances, making these insects especially challenging agricultural pests. Most grasshoppers don’t undergo this change, even in large groups. While there are some species of grasshoppers that can cause environmental damage, the species that invaded Las Vegas weren’t on the same level.

Grasshoppers in Las Vegas Were Harmless

Grasshoppers are drawn to bright light, so the multiple beams shining from Las Vegas' famous hotels and casinos helped display thousands of insects flying through the air once the sun went down. Since the species doesn’t sting or bite, doesn't carry disease, and wasn’t likely to cause much damage, officials urged people to simply leave the grasshoppers alone and allow them to move on.

In large numbers, other species of grasshoppers can infest residential gardens or large scale crops, causing extensive damage. After a couple of weeks, the populations began to drop as the grasshoppers were eaten by predators or continued to move north out of the city.

Will It Happen Again?

Entomologist Jeff Knight of the Nevada Department of Agriculture told the Associated Press that, although the numbers were high, they weren’t completely unprecedented. The department had records as far back as the 1960s of Las Vegas swarms due to increased rainfall. In fact, Knight could even recall a couple of similar migrations during his own career, including one just six or seven years prior.

Most experts agree that the climate crisis could intensify rainfall in the future. In March 2020, a study published in the Proceedings of the National Academy of Sciences found that environmental risks will increase as the atmosphere continues to warm. According to the study, extreme rainstorms that previously occurred once every 20 years will happen every five years in North America if the current level of warming caused by greenhouse gas emissions continues; the Earth could heat up by a whopping 5.4 degrees by the year 2100, in which case 20, 50, and 100-year rainstorms may occur every 1.5 to 2.5 years.

View Article Sources
  1. Roussi, Antoaneta. "Why Gigantic Locust Swarms Are Challenging Governments And Researchers." Nature, vol. 579, no. 7799, 2020, pp. 330-330., doi:10.1038/d41586-020-00725-x

  2. Anstey, M. L. et al. "Serotonin Mediates Behavioral Gregarization Underlying Swarm Formation In Desert Locusts." Science, vol. 323, no. 5914, 2009, pp. 627-630., doi:10.1126/science.1165939

  3. Kirchmeier-Young, Megan C., and Xuebin Zhang. "Human Influence Has Intensified Extreme Precipitation In North America." Proceedings Of The National Academy Of Sciences, vol. 117, no. 24, 2020, pp. 13308-13313., doi:10.1073/pnas.1921628117