Remember the invasion of grasshoppers? Now there’s an explanation

ST. GEORGE — In the summer before the current pandemic, Southern Utah was dealing with another plague: Grasshoppers. 

A grasshopper hitches a ride on the hood of a car in St. George, Utah, July 28, 2019 | Photo by Chris Reed, St. George News

A grasshopper invasion that was mainly inflicted on the Las Vegas area bled into Southern Utah in the summer of 2019, peaking in July. Many residents will remember getting to their cars to see the hoppity insects all over their windshields during the day and fluttering all over streetlights at night. Walking on a lawn had the creatures popping out like popcorn in hot oil.

At the time, scientists didn’t really have an answer to the insect invasion. But now, a new study has a peer-reviewed theory: It was all about the light. 

The study, led by the University of Oklahoma’s Department of Biology, said the reason for the grasshopper explosion was two-fold: an abundance of vegetation in the Nevada/Utah area from a wetter-than-usual winter in late 2018/early 2019; and the lights of Las Vegas acting as a beacon drawing the grasshoppers throughout the southwest deserts like a moth to lamplight.

St. George News spoke with the study’s lead author, Elske Tielens, an insect ecologist at the university, who said the lights of Las Vegas had bled off into Mesquite and St. George.

“There was a big population of grasshoppers that year, and St. George may produce enough artificial light or sky glow to similarly have drawn in large numbers of grasshoppers,” Tielens said. 

A gif showing a radar map from July 2019 shows the growth and spread of a grasshopper swarm in the Desert Southwest. | Photo courtesy of University of Oklahoma, St. George News | Click to enlarge and set in motion

The researchers utilized radar data and determined that Las Vegas alone had about 46 million grasshoppers buzzing around the city on a July 2019 night. In a video of that data, seen with this article, the grasshopper population looks like a large bonfire atop Sin City, with the grasshoppers appearing as flames casting northwest – right toward the dots of light that are Mesquite and St. George. 

The researchers also looked at vegetation data and drew a correlation between the large growth in vegetation in the Southwest and the light pollution as duo draws.

“That region had a wet winter and spring, which tends to result in large grasshopper populations. In wet years, more eggs survive and hatch, there’s more vegetation for the juvenile grasshoppers to eat, and so you can get these big population sizes,” Tielens said. “And that’s a key point too – that it takes both the artificial lights and the large population of grasshoppers in the region to draw in these kinds of millions of individuals.”

Any resident is familiar with seeing insects – from moths to gnats – swarming around their porch lights, especially in the summer. A night view of the area between Las Vegas and Southern Utah seen from space shows Las Vegas as one bright beacon in a seemingly pitch-black sea, with Mesquite and St. George looking like little light islands to the northeast. 

A December 2019 image from the Suomi NPP satellite shows the Desert Southwest, with cities including St. George and Las Vegas labeled. | Photo courtesy of NASA/NOAA, St. George News | Click to enlarge

While the lights haven’t dimmed, the current drought alerts show that the lack of a wet winter is likely to prevent a repeat of the grasshopper invasion this summer. 

But Tielens said that doesn’t mean the 2019 takeover of the tiny creatures stands as a once-in-a-lifetime event. The beacon of lights is only getting brighter, she said, and it might just take another El Nino winter of high rainfall to bring another grasshopper and insect inundation.

“I can’t predict the future, but grasshoppers are an integral part of the ecology in rangelands out west, and hopefully will continue to be in the future. Human impact on the environment through brightening the night sky is only increasing, and so the effects of artificial light on grasshoppers and insect populations generally will continue,” Tielens said. “Your readers are likely not sad to see grasshopper numbers go down, but long-term negative impacts of artificial urban lights for various insect species will likely become a bigger conservation concern.”

Copyright St. George News, LLC, 2021, all rights reserved.

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