Ravenous armyworms are eating their way across China

A farmer in India shows an armyworm-infested corn shoot.
A farmer in India shows an armyworm-infested corn shoot.
Image: Reuters/Rajendra Jadhav
We may earn a commission from links on this page.

Foreign invaders have conquered China. An all-out battle is looming. But the attackers are a far cry from the northern barbarian hordes of yore. Rather, they are mud-colored grubs from the Americas, whose deadliest weapon is their appetite.

Which is, to be clear, titanic. Armyworms (or Spodoptera frugiperda) are more than your average very hungry caterpillar. They’re larval eating machines—feared by farmers from Argentina to Florida for turning hundreds of acres of cropland into vegetal stubble, all in a single night.

Another weapon is their “live fast, die young” ethos. Armyworms don’t live long—only about a month in the summer, and maybe a couple more in colder months. But oh, how they breed. After reaching adulthood—aka transforming into a moth—a female lays around 1,500 eggs in the 10-day life stage. And then there’s their wanderlust. By hitching a ride on wind currents, armyworm moths can travel between 100 and 500 kilometers (about 60 to 300 miles) in one night, according to Xinhua News (link in Chinese). This helps explain why they appear almost exclusively in Biblical plague-scale numbers—and spread at a pace that’s devastatingly swift.

Take, for example, China’s current infestation. In January, farmers near the Myanmar border first noticed the worms. Now, less than six months later, the infestation spans the entire southern half of China. And it’s gaining speed. In mid-May the worms destroyed 200 square kilometers of crops in less than two weeks, according to Caixin Global, a respected Chinese economic magazine. Warmer temperatures could accelerate armyworm reproduction. Since they hail from the Americas, they have no natural predators. (Their native range runs roughly from the southern US to Argentina, where they are held in check by things like parasite insects, pesticides, and in cooler regions, freezing temperatures. And it helps that farmers there have been fighting them for centuries).

The timing of the armyworm incursion is very bad indeed. The Chinese economy is slowing. Thanks to African swine fever, which has wiped out about a fifth of the country’s pork supply, food prices are already climbing, leaping 7.7% in May, versus the same month a year ago. The armyworm outbreak is at risk of exacerbating that trend. A sharp enough rise in food staple prices will leave consumers with less income to spend on other goods—a hit to demand that could drag on growth even more. (And though a grain and vegetable shortage in China might benefit US farmers, the tariffs China imposed on American agricultural products certainly won’t help curb prices.)

Despite the alarming swiftness of the infestation, grain prices have so far stayed flat. For now. But the armyworm swarms now hover on the edge of the North China Plain, the country’s top grain-producing region, which is scary news. Armyworms aren’t picky eaters (a trait that helps them spread) but they love corn. On its native continent, the pest has caused corn crop losses of between 40% and 70%. Merely staving off infestation costs Brazil $600 million each year, reports The Guardian.

Fortunately, they’ve been mostly contained to the Americas—until 2016. It was then that they first appeared somewhere they really shouldn’t: Nigeria. How’d they get there?

Probably not by flying. Even though armyworms have been found on oil rigs 100 miles off the coast of Mexico (registration required), there’s no way they flew across the Atlantic. Instead, they must have stowed away on cargo, likely on a trip from Florida (link in Chinese).

Whatever the case, African farmers had no defenses prepared, and agricultural losses across the continent have been catastrophic, devastating farmers and threatening food security. While one estimate projected Africa lost $3 billion in one year (paywall), that number could be as high as $6.2 billion, Xinhua says. After colonizing Africa, the wormy shocktroops of infestation crept stealthily on. From a beachhead in Gujarat cornfields (pdf), they took India. Then Sri Lanka and Thailand. Next on to Myanmar.

And then southern China. The damage there is only beginning to be calculated but according to one recent estimate, the southwestern province of Yunnan alone is already facing at least 200 million yuan ($29 million) in losses (link in Chinese). 

With the armyworm barbarians now at the gates of China’s corn belt, the government is pulling out the big guns. Namely, stinkbugs.

China’s top research institute is now preparing to “fight pests with pests,” raising these predatory insects by the millions, with a mind to deploy them against the caterpillar invaders (link in Chinese). Stinkbugs kill by paralyzing their armyworm prey, then sucking the moisture out of the boneless body. One of the stinkbug species being tested can dispatch more than 40 armyworms a day, according to the research institute. The institute has set up facilities for breeding 10 million stinkbugs annually, according to Bloomberg.

This might sound kind of crackpot. After all, why not just zap them with poison?

That’s already in the works. In May, China’s agriculture ministry directed local officials to advise farmers on effective use of pesticides.

But chemical pesticides are expensive. They’re also hard to use effectively against armyworms; because the volume of food the caterpillars consume increases exponentially as they grow, by the time farmers notice crop damage, they’re usually too thick on the ground to be eradicated in time to save the crops. Part of the problem is that armyworms tend to bore deep into their crop quarry as they grow, putting them out of the reach of insecticides.

The stink bug plan could well work. Known as “biological control,” the technique involves introducing a predator to control the population of some undesirable critter—kind of like adopting a cat to keep out mice. There is, indeed, a long history of successful efforts. (The first, as it happens, dates back to 304 AD, involving ants in southern China.)

Some of those successes include fighting armyworms. To combat infestations, farmers in parts of the Americas have used native insect predators known as parasitoid wasps. (These critters lay their eggs inside other insects. A hatchling bides its time by feeding on its host’s insides until it finally bursts forth, Alien-style—an event that usually results in the host’s death.) China’s stink bug phalanxes might not be quite so sci-fi in their killing. But let’s hope they’re as brutally effective. Experts in southern provinces have already observed several armyworm generations—hinting how frighteningly easily the invasion could become permanent.