Locust Swarms Are Getting So Big That We Need Radar to Track Them

The desert locust upsurge is yet another of 2020’s horrors

Photo: Jasius/Getty Images

In June, remote sensing analyst Raj Bhagat noticed a strange signal on India’s weather radar. It looked like a small band of rain near Delhi, moving southwest, but Bhagat was convinced it was a locust swarm.

“People began to report it,” he says, referring to sightings on the ground. Giant locust swarms had spread to northern India earlier in the year, ravaging crops and destroying people’s livelihoods. “The timelines were perfectly matching.”

In mid-July, Bhagat, who works at the World Resources Institute India, identified a similar formation, this time near the city of Lucknow. He posted it to Twitter with the hashtag #LocustsAttack.

The desert locust upsurge is yet another of 2020’s horrors. In dry years, the insects, which can grow up to four inches long and are shades of green, black, or yellow depending on their life stage, remain localized to the deserts of Africa, the Middle East, and southwest Asia. Lately, however, the weather has been wetter than usual. Desert locusts have bred prolifically and migrated in huge swarms to countries that don’t always see them in large numbers, including several nations along the horn of Africa. Other places, such as the state of Uttar Pradesh in India, haven’t had a locust invasion in decades.

The locust outbreak is currently classed by the United Nations Food and Agricultural Organization (FAO) as an “upsurge.” If the insects begin migrating in large bands — which could happen within a couple years, should things worsen — they’ll be officially considered a plague.

A swarm covering one square kilometer eats as much food as 35,000 people every day. The damage done so far is already appalling. The UN says the food supply of 25 million people in East Africa has been threatened by the insects. In Ethiopia alone, they’ve destroyed around 200,000 hectares of crops. Meanwhile, in India, the insects have chewed up 50,000 hectares.

The recent outbreak may be just a hint of what is to come, thanks to the extreme weather expected as a result of climate change. Such conditions, including periods of excessive rainfall, would be adored by the locusts, says Keith Cressman, senior locust forecasting officer at the FAO.

The locusts’ wanderlust has sparked efforts to develop tools to closely track the insects. The FAO already uses real-time reports from locust survey teams on the ground and satellite imagery of vegetation and weather events to help forecast how many locusts will breed and where they will go. Countries use data on locust migrations to determine where to send teams in efforts vanquish the insects en masse by dropping pesticide on them from planes. Among the technologies that could improve locust surveillance by pinpointing locations of multiple swarms at a given moment are radar and drones.

The idea of using remote sensing technologies like radar to spy on locust swarms is not new. A 1955 letter in the journal Nature reported the first such sighting on British naval radar the previous year. HMS Wild Goose had detected a humongous 48-kilometer-wide swarm of desert locusts flying over the Persian Gulf.

Bhagat says he thinks his sightings are the first weather radar detections of locusts in India, though his observations haven’t been confirmed yet. Ryan Neely III, an atmospheric scientist at the University of Leeds in the U.K., is building a specialized system to do the same kind of analysis. It is absolutely possible to use weather radar to spot the insects, he says. They are, after all, not that dissimilar from large raindrops.

“They are just gooey bags — goo or water surrounded by a hard shell,” Neely says.

He and his colleagues have scanned desert locust specimens in 3D, allowing them to predict the electromagnetic signature of a single locust — and, by extension, what a whole swarm of locusts would look like on radar. The model can also account for the particular behavioral properties of locusts: Unlike raindrops, they stay aloft until they are ready to land.

“They are just gooey bags — goo or water surrounded by a hard shell.”

In theory, a system trained to identify blotches on radar that look like locust swarms — as opposed to rain clouds or flocks of birds, which appear as similar blotches — could be automated. Locust swarm surveillance, 24/7, could be a boon to countries seeking to better target their pesticide response, since most locust surveillance still relies on data collected by hand.

One stumbling block, however, is the availability of weather radar in those regions worst affected by desert locusts, Cressman notes. Africa is almost entirely without such systems. Bhagat adds that they are also sparse in India. “Not even a 20% area might have been covered by these radars,” he says, referring to parts of the country lately blighted by locusts. While potentially useful in some places, radar-based detection clearly wouldn’t be possible everywhere.

Satellites can also be used, in principle, to spy on locusts from orbit. But such high-resolution data is even harder to come by, Cressman says.

For his work at the FAO, Cressman relies partly on data uploaded by specialist locust-spotting teams on the ground in around 20 countries in Africa, the Middle East, and southwest Asia. These teams have at their disposal a rugged tablet computer with a special app through which they can report locust swarms. The tablet is connected via satellite to each country’s National Locust Control Centre. Cressman also gets the data at his office in Rome, Italy.

“We know exactly, within less than a minute, where the teams are, and we also know where the locusts are,” he says.

The data the FAO receives every day, Cressman says, influences the publication of warning notices for countries where locusts could migrate next. The FAO warned Sudan of one such migration back in May, for example. Alerts allow locals time to organize pesticide-spraying operations.

The FAO’s system is called eLocust3. Earlier this year, Penn State University released a simplified version of the eLocust3 app that can be installed on most Android phones — an effort to expand the number of people who can make locust swarm reports to the FAO. The new app has been downloaded more than 5,000 times.

“The best source of information will always be a well-trained person,” Cressman says. But on the other hand, well-trained locust spotters can’t be everywhere at once. And during major upsurges like the one seen this year, additional locust surveillance tools become all the more useful.

That’s why the FAO has been experimenting with drones to widen the reach of locust survey teams. The drones can map areas of 100 square kilometers or so to detect green vegetation that may be harboring locusts. They can also gather optical imagery to detect the insects themselves. After four years of experiments, the drones are now ready to be deployed for real, Cressman says.

“As soon as these Covid-19 travel restrictions are lifted, we will be putting in teams of drones,” he says.

Even bigger locust upsurges and plague events were seen in the early and 20th century, Cressman says. But there is a possibility that in the coming years, the desert locust populations will explode once more. Locust forecasters need all the data they can get, which is where drones and high-speed communications may come in handy.

“You have to approach it almost in a military, systematic manner,” Cressman says. “It’s like a war, you know.”

Freelance science and technology journalist. Based in Northern Ireland.

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