As the coronavirus pandemic exploded across the world earlier this year, another even more conspicuous plague was tearing through East Africa: locusts. The voracious little beasts are particularly fond of carbohydrates like grains, a staple of subsistence farmers across the continent. Back in January, the UN Food and Agriculture Organization (FAO) predicted the worst was still to come, and that by June, the size of the swarms could grow by a factor of 500.

And now, at the worst time, a second wave of locusts 20 times bigger than the first has descended on the region, thanks to heavy rains late last month, according to the FAO. The swarms have infiltrated Yemen and firmly established themselves across the Persian Gulf, having laid eggs along 560 miles of Iran’s coastline. New swarms are particularly severe in Kenya, Ethiopia, and Somalia.

"The timing is really horrendous, because the farmers are just planting, and the seedlings are just coming up now since it's the beginning of the rainy season," says Keith Cressman, senior locust forecasting officer with the FAO. "And it's right at the same time when you have an increasing number of swarms in Kenya and in Ethiopia. There's already pictures and reports of the seedlings getting hammered by the swarms. So basically that's it for the farmers' crops."

“This represents an unprecedented threat to food security and livelihoods,” FAO officials wrote in a brief last week. All this is happening while the region locks down to stave off the coronavirus pandemic, and as travel restrictions mean experts can't get to countries to train people. It’d be hard to imagine a more brutal confluence of factors. “The problem is that most of the countries were not ready, and are now invaded with swarms,” says ecologist Cyril Piou, of the French Agricultural Research Center for International Development, which helps economically developing countries with agricultural issues. “The solution is to try to control as much as you can.”

It would also be hard to imagine a more perfect enemy than the locust: in this case, the desert locust, one of the 20 species of normally solitary grasshopper that go “gregarious,” forming into swarms that can travel 90 miles in a day. Their transformation and swarming is triggered by rain; desert locusts can only lay their eggs in moist sand, since dry sand would cook them. After a storm, the locusts breed like crazy, packing a single square meter of sand with perhaps 1,000 eggs.

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When those eggs hatch, the baby locusts find themselves in a newly lush environment loaded with food. They’ll strip it clean and take off in swarms in search of ever more vegetation to obliterate. Their bodies actually transform to prepare them for the journey; their muscles grow bulkier, and their color changes from a drab brownish green into an electric yellow and black. This color shift probably has to do with the gregarious locusts now eating the toxic plants they had previously avoided as solitary insects: That bright coloration warns predators that they’re toxic as a result of their diet. If they were this color when they’re solitary, they’d stick out to predators, but as they gather in their billions, it’s not like they need to be inconspicuous anymore. There’s safety in extreme numbers.

This particular outbreak began with heavy rains from two cyclones in May and October of 2018 that hit the southern Arabian Peninsula. This allowed two generations of desert locusts to form into swarms. Each generation can be 20 times bigger than the previous one. “The main problem is that these exceptional rains occurred in an area where there's a lot of insecurity, wars, and so on, so the initial stages of the upsurge of the outbreaks were not detected in time,” says entomologist Michel Lecoq, former director of the French Agricultural Research Center for International Development.