The caterpillar larva of a fall armyworm. Photographer: Waldo Swiegers/Bloomberg (Bloomberg)

The fall armyworm is hungry, on the move and scaring farmers the world over. The crop-devouring pest has spread from the Americas to Africa and Asia, gorging on rice, corn, vegetables, cotton and more. Europe, Australia and Southeast Asia could be next. In its first three years in Africa alone, it inflicted $13.3 billion of crop losses. A recent arrival in China, the fast-moving grub may infest the country’s entire grain-producing farmland within a year. With food supply chains already facing disruption from the trade war and a global epidemic killing pigs, the world is bracing for the advance of what’s been called the “pocket-sized monster.”

1. What is the fall armyworm?

It’s actually a caterpillar, not a worm. Fall armyworm (Spodoptera frugiperda) is native to the North and South American tropics and measures about 3-4 centimeters (1-1.5 inches). The grubs have a distinctive upside down Y on their heads and four dots on their second-to-last segment. They get their name from the way they advance en masse with military precision, feasting on the leaves and stems of some 186 plant species, including economically important crops such as wheat, soybeans and sugarcane.

2. Why are they such a dreaded pest?

The aggressive munching can denude crops, cutting corn yields by 20-50% and sorghum by 16%. What’s more, a female moth can lay as many as 1,000 eggs during her lifetime, reproduce in a month under favorable conditions and fly up to 100 kilometers (62 miles) in a single night. Multiple generations can traverse some 2,000 kilometers during the species’ annual migration. They are so ravenous that the young caterpillars feast on their own siblings, ensuring that only 1 to 3 fully grown larvae remain on each plant.

3. How are they spreading?

They were detected for the first time in Africa -- in the western nations of Benin, Nigeria, Sao Tome and Principe, and Togo -- in early 2016, possibly introduced via trade or weather systems associated with El Nino events in 2014-2016. The fall armyworm is now in virtually all of sub-Saharan Africa. In July 2018, it was confirmed in India and Yemen. By January, it had been reported in Bangladesh, Myanmar, Sri Lanka, Thailand and China. Corn farmers on the Indonesian island of Sumatra have reported infestations there since March.

4. What’s the impact in China?

Advancing from China’s southern border, the pest had affected grain production in 18 provinces covering more than 90,000 hectares (222,400 acres) as of early June. Authorities have employed an emergency plan to monitor and respond, but it’s predicted fall armyworm will reach the corn belt in the northeast during the summer. There’s a “high probability” that it will spread to the entire country’s grain-producing area in the next year, the U.S. Department of Agriculture says, since most farmers don’t have the means or training to effectively manage it. That may push them to grow crops that aren’t susceptible, such as cassava and sweet potatoes. The damage to existing crops and any switch to new plants might exacerbate disruptions to food supply caused by a nationwide outbreak of African swine fever and an ongoing trade war with the U.S.

5. Where will it go next?

That depends on the weather. Fall armyworm has only invaded areas with a climate similar to its tropical home. In China, it’s projected to move northward as spring temperatures rise and crops develop along major growing areas in the center, north and, eventually, the northeast. Seasonal factors, such as the timing of the monsoon and the number of typhoons, will influence its movement and impact. South and Southeast Asia and Australia also have favorable climates, not to mention strong trade and transportation links with infested countries, putting Australia, Malaysia and the Philippines at high risk. Fall armyworm’s advance into Europe is harder to predict. Small areas of Spain, Italy and Greece might provide suitable conditions, but in general low temperatures halt the pest’s advance.

6. What can be done?

Crops genetically engineered to express genes from the soil bacterium Bacillus thuringiensis are protected, without the need for broad-spectrum chemicals that may harm beneficial insects. Problem is, some fall armyworm strains have developed tolerance to that naturally occurring deterrent. The Chinese Academy of Agricultural Sciences has identified 21 chemical pesticides that could mitigate the caterpillar’s spread and impact. Scientists with the academy’s Institute of Plant Protection are seeking to deploy an army of predatory stink bugs, a natural enemy of fall armyworm. Early detection is essential as the pest can only be effectively controlled with insecticides while larvae are small. The non-profit Centre for Agriculture and Bioscience International offers more rudimentary advice: “See it. Squash it. Stop it.”

--With assistance from Niu Shuping.

To contact the reporter on this story: Jason Gale in Melbourne at

To contact the editors responsible for this story: Michael Patterson at, Grant Clark, Tony Jordan

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