Farmers, golf course managers and lawn-lovers across the nation are under attack. The enemy is about the length of two postage stamps, mean, sometimes green and certainly hungry.

Battalions of fall armyworms are eating their way through fields and crops — sometimes overnight. Entomologists say they haven’t seen an outbreak this aggressive since the 1970s, and while it’s too early to be certain, climate change could be playing a role in the scourge of caterpillars munching through crops east of the Rockies.

One entomologist estimated that millions of acres of the United States have been affected by armyworms. The bugs are particularly destructive, experts say, causing more damage more quickly than most pests.

Armyworms get their name from the way they march in unison across swaths of land. Ashley Dean, an extension entomologist at Iowa State University, said she’s heard stories of people who see a mass of something creeping alongside a road, and when they get out of their cars, it’s a tangle of armyworms headed toward their next meal.

Nick Elchinger, a farmer in Deshler, Ohio, said he’s never seen anything like the havoc the worms wreaked on his fields this summer.

One Friday, Elchinger noticed a couple of armyworms on the outskirts of some of his alfalfa fields. There were only a few, he said, so he figured he would deal with them over the weekend. “But by Sunday, the field was completely overtaken by bugs,” he said. In two days, the worms had stripped his alfalfa down to its stalks, chewing off essentially every leaf, Elchinger said. “It was shocking,” he said. “I’d never seen nothing like it.”

Experts say weather conditions created a perfect storm for this summer’s explosion of armyworms. The worms, which are actually moth caterpillars, generally don’t hatch until later in the season, so their early emergence caught farmers off-guard. They’re also generally difficult to detect since they feed late at night or early in the morning and tend to hide in leaf litter or stay on the soil’s surface during the day.

Fall armyworms differ from true armyworms, which are less destructive and have a more restricted diet. But unluckily for farmers, fall armyworms aren’t picky eaters. They’ll tear through vegetables, grains, grasses and more. The caterpillars are often brown or greenish and can be identified by a Y-shaped marking between their eyes.

“When they hatch, the caterpillars are hard to find. You’re not going to notice them,” said Katelyn Kesheimer, an entomologist with Auburn University and the Alabama Cooperative Extension System. “But the problem is when they’re about a week-to-a-week-and-a-half old, and they just start feeding like it’s going out of style.”

A study published in January from the International Journal of Pest Management found that climate change can prompt fall armyworm outbreaks.

A mild winter in the southern United States allowed more of the moths to survive than usual, Kesheimer said, and more frequent storm fronts carried them north to lay scores of eggs.

“My guess is that we won’t see as many years between each of these historic infestations anymore,” Kesheimer said. “They’re going to become more widespread, and so we really need to take that into account across all systems, just to make sure that we’re ready for it.”

Pete Landschoot, a professor of turf grass science at Pennsylvania State University, said he sees this more as a one-off event that is bound to happen every few years. That’s a relief, he said, because early detection is unlikely unless you get down on your hands and knees to search for signs of the caterpillars.

That said, experts say farmers should monitor their fields for unusually high numbers of birds, which could be drawn in by the feast of caterpillars, and concerned growers could use sweep nets to see if the caterpillars are present in their crops.

Armyworms tend to do the most damage to small plants early in the season, and they’re the most destructive as they reach the end of their larval stage and start preparing to form cocoons.

When the caterpillars have passed through a field or lawn, it looks like sheer devastation, Landschoot said. It’s not that patches of a lawn or field have browned — nearly the entire swath of land has been wrecked. Dean said the way they strip away foliage can look similar to hail damage.

Landschoot said more mature lawns can often recover from an armyworm attack. “The good thing is a lot of these lawns recover,” he said. “Now if they got into a lawn where it was just recently seeded, forget it. It’s gone.”

Landschoot said a lot of armyworm destruction was mistaken for disease earlier in the season. People weren’t expecting them. “You can get infestations every couple of years, every few years, but a big one like this is extremely rare,” he said. “And probably the biggest infestation that I’ve ever seen of any kind of leaf and stem feeding insect on turf.”

If detected early enough, armyworms can be killed with insecticides. But experts say the window for that treatment is small, and people whose lawns are affected by the pests might just want to wait for regrowth.

Kesheimer also said the worms are so pervasive that the most effective kinds of insecticide are sold out in several regions.

The United States could be seeing fallout from this outbreak for months, Kesheimer said, since the caterpillars destroyed hay across the nation that farmers were saving to feed their livestock over the winter.

Now it’s a waiting game until it gets cold enough to kill off the moths and prevent another generation from hatching this year. “We’re just kind of biding our time until we get some cold weather here in the U.S. and they can stop doing their damage,” Kesheimer said.

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