Science

Grasshoppers Are Descending on the West in Swarms

Many grasshoppers fly through the air.
Swarms of grasshoppers are seen over the agricultural fields in Jijiga, Ethiopia, on Oct. 31. Minasse Wondimu Hailu/Anadolu Agency via Getty Images

If you’ve been disappointed by the recent absence of hordes of cicadas across the United States, don’t worry: Grasshoppers are here to plug that bug-shaped hole in your heart. They’re also here to eat huge swaths of cropland, denude trees and other plant life, and generally wreak havoc on the West and its agriculture.

Thanks to extreme drought conditions and last year’s fairly large population of the dry climate–loving insect, concerningly dense swarms of grasshoppers are descending on the Western United States. The outbreak is causing concern amongst farmers across the West, from Utah to Wyoming to Montana, who are worried for their crops and livelihoods: Oregon rancher Richard Nicholson described the insect swarms as “a scourge of the Earth” to the Guardian. At the same time, conservationists warn of adverse impacts from widespread insecticide usage. The swarms are an issue many of us might recognize best from the Little House on the Prairie books (or, perhaps, the Bible), but—other than making our skin crawl—what threat do the giant black clouds of insects really pose, and what’s the best way to deal with them?

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Slate spoke with Scott Schell, an entomologist who studies rangeland grasshopper ecology and management at the University of Wyoming, about the grasshopper invasion and what’s being done to minimize the damage. Our conversation had been edited and condensed for clarity.

Grace Woodruff: First of all, how many grasshoppers are we really talking about here?

Scott Schell: If you piled all of the grasshoppers in outbreak areas in the West into one pile … it’d be quite numerous. But some of the reports have made it sound like the entire West is awash in grasshoppers, and that isn’t really true. We do have areas in some states that are heavily infested.

We’re really not too concerned with grasshopper numbers until they get up to at least 14 per square yard on rangeland. For perspective, 15 adult two-striped grasshoppers per square yard—they’re a large species—equals about 100 pounds of grasshopper per acre. If bunched together, it would be like a small sheep that can eat its bodyweight each day of green forage on each acre of range.

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This year, we’re talking about, in some places, maybe 50–60 grasshoppers per square yard. In certain areas, they can get up even higher than that.

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This is bad for farmers because it’s damaging to crops, right?

In some cases it’s not even so much that they’re going to eat the leaves off the crop—in this year, in hot, dry conditions, a grasshopper swarm can land in a field of small grain, and they’ll clip the heads off the grain and get some moisture from the stalk. They’re not even really eating the grain, but they’ve made it unavailable for harvest.

Grasshoppers easily outcompete larger animals for grass. They consume way more, in proportion to body size than, say, livestock. When they’re growing, in the nymphal stage, grasshoppers can eat more than their body weight per day in wet vegetation. And, in some species, they waste even more. They’ll walk up to a blade of grass, clip it, eat what they want, and drop the rest. They can eat it right as it grows out of the ground. They’re tiny; they’ve got small mouthparts. As the blade tries to grow, they’ll just munch it right off. They’ll stay fat and happy while everything else is dying.

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What’s making this year’s invasion so special, or so especially concerning?

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When you have drought weather, it exacerbates the grasshopper issue. The unprecedented extent of the serious drought in the West, combined with grasshoppers: You’re in bad shape.

Montana has started spraying an aerial pesticides to kill grasshopper nymphs before they can develop into adults. Is that the right way to address the problem? Conservationists have pushed back on insecticide use as a strategy for controlling grasshoppers, claiming that they might do more harm than good to the insect population and the ecosystem as a whole. 

What we [at the University of Wyoming Entomology Extension] recommend is an integrated pest control strategy, where you treat every other swath [of land], so you have untreated areas in the grasshopper outbreak. Grasshoppers are highly mobile, so you don’t need to spray every place—they’ll move over and get into a treated swath from an untreated swath. We take advantage of the grasshopper’s gluttony: They eat a lot, so we can put the insecticide out in really small amounts.

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Do grasshoppers do anything useful, or are they just pests?

Oh no, the grasshoppers are part of the wildlife out on the range! They provide food for other organisms, like our songbirds. But we need to manage them. The grasshoppers at this point in time, if they’re wisely managed with integrated pest management, it’s better than just letting them go. We have to make a decision: Can we maintain agriculture on the Great Plains and grasshoppers, without harming the environment? I think the answer is yes.

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Are swarms of insatiable grasshoppers going to be common in years to come, or is this more of a one-year-only invasion?

Grasshoppers, they can persist. When I was doing research for my thesis—a long time ago—I looked at historic records. We’ve seen places where an outbreak would persist for several years. Eventually, with no intervention, the grasshoppers would succumb to weather events. When they hatch in the spring, they’re about the size of a grain of rice, so they’re pretty vulnerable. They’re all native, these grasshoppers, so there’s also a whole host of other arthropods and insects—even mice—that feed on them and help to suppress the grasshopper population. The other thing is it can get so bad in a drought, with less forage, that grasshoppers who can’t migrate will starve out.

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How long have grasshopper swarms been happening?

A long time ago, a professor of mine was doing research on the glaciers Wind River Range. There’s some in Montana and some in Wyoming called “Grasshopper Glaciers” because when people visited those areas they’d often find grasshoppers emerging from the toe of the glaciers. What that was was swarms of the Rocky Mountain locust, riding the winds, which took them to the top of the glacier, where they got too chilled to fly anymore, so they were slowly incorporated into the glacier and eventually spit out the bottom. In those, we essentially have a historic record of grasshopper outbreaks [from hundreds to possibly thousands of years ago], at least the times when swarms flew into the mountains.

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As someone who’s spent quite a bit of time studying insects, how do you really feel about grasshoppers? Is their reputation as “pests” warranted, or do they have some redeeming qualities?

At low—or I guess you could say “normal”—grasshopper population densities, I find them fascinating. They play an important role on the rangeland. I think probably all the large mammals could disappear and have less of an impact on the rangeland than if all the grasshoppers disappeared. Grasshoppers play an important role out there. But, when they get to be really thick, like an outbreak where you have 50 or 100 grasshoppers per square yard and they’ve eaten everything down to the dirt, they’re obnoxious. I guess I’m kind of split. I’m really fascinated by them, but as a pest, I can see why people hate them.

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