Why did 45 million grasshoppers swarm Las Vegas in 2019? Bright lights weren't the only factor.

Dustin Barnes, USA TODAY
·3 min read

In the summer of 2019, the bright lights of Las Vegas drew in more than just tourists looking to gamble and party. The glow of the famed strip also was responsible for summoning some 45 million grasshoppers, according to a recent study.

"It turns out Las Vegas gets fewer people to come gamble in the course of a year than the grasshoppers in the sky on that single night," said Elske Tielens, a researcher at the University of Oklahoma and one of the study's authors.

That night, July 26, 2019, brought a swarm of grasshoppers so massive that it appeared on weather radar. And Tielens said it's safe to assume there were more grasshoppers on the ground than the ones they could quantify by just using radar.

So why was 2019 the year the grasshoppers tried their luck in Vegas?

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It turns out this mass insect incident was the meeting of two events, Tielens said. "One side is the bright dome of light over Vegas, the brightest city in the U.S. But on the side, you need this really large population of grasshoppers."

And that booming population was the result of a wetter winter and spring which had created more vegetation for the grasshoppers to feed, she added.

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Though swarms of insects may bring biblical themes to mind, these grasshoppers didn't decimate the area's vegetation. They didn't bite and torture Nevadans or wildlife.

However, this massive swarm did create a nuisance for tourists and residents, scaring them from going out or just scaring them in general, Tielens said. And it's likely this gathering of grasshoppers made their natural predators very happy. Birds in the area, for example, had more food which can translate to healthier eggs, better nest survival rates and therefore more chicks the following year.

Swarms of insects taking over cities or vast regions aren't totally unheard of in the U.S. In 2020, New Orleans was covered with mayflies, a harmless insect that appears much more sinister when seen in large groups. Fifteen states and Washington D.C. are currently bracing for billions of periodical cicadas to come forth in the next month or so.

Future environmental factors, such as temperatures and rainfall totals, will continue to influence which years are bumper crops for insect populations and therefore candidates for more swarms. But experts say humans also play a big part in determining when, and if, the next big swarm takes place.

Manmade structures, aside from just nighttime lights, can draw in insects like the mayfly en masse, said Luke Jacobus, associate professor of biology at Indiana University-Purdue University Columbus.

"Roadways solar panels can be problematic for mayflies. They think those are water, so they’ll engage in their reproductive behavior and lay their eggs there," Jacobus said. "Shiny services and dark services also decrease the potential new (mayfly) population."

Mayfly swarms are smaller than they have been in past years, Jacobus said, partially due to water pollution.

"As we're doing a better job of taking care of our fresh water and managing habitats, the mayfly numbers are increasing."

This article originally appeared on USA TODAY: Las Vegas lights contributed to 2019 grasshopper swarm, study says