By EMMA BRYCE
The United Nations Food and Agriculture Organization warns that large swarms of locusts are forming in Africa’s Sahel region and are likely to push northward to Algeria, Libya, Morocco and Mauritania once they take flight. The origins of the threat probably date back to a year ago, when rains drew in a wisp of desert locusts to Libya and Algeria, said Keith Cressman, the senior locust forecasting officer for the F.A.O.
The swarm is thought to have originated in the Libyan conflict zone, where obstacles to monitoring allowed a fast-breeding population to double up and form two generations, which then settled and laid eggs in countries to the south, he said in an interview.
Now, with an unusually lush moist summer just past, another two succeeding generations are forming in Mali — where monitoring is also hampered, by an Islamist uprising — and will soon form in Chad and Niger, the organization said. From there, they are expected to head north to greener pastures, posing a major threat to harvests and food security.
Unable to steer their own course, the insects are “victims of the wind,” Mr. Cressman said in a telephone interview. Still, they have some ability to choose the currents that guide them: they tend to catch breezes with promising scents.
Each swarm consists of billions of locusts. “The situation we face now, it’s the most serious since the last regional plague,” which unfolded from 2003 to 2005 in West Africa, he said.
The very sight of a swarm can conjure biblical tales. On one field visit to Sudan in the 1980’s, Mr. Cressman said, he recalls seeing a “low dark smudge” that blocked out the sun and blackened a quarter of the sky. Another time, he saw locusts rise up in what seemed akin to a giant cumulonimbus cloud that blocked out the sun.
The locusts eat their weight in food every day. “If you take a swarm that’s the size of Manhattan, in one day that swarm can eat the same amount of food that everyone in New York [State] and Pennsylvania will eat in a day,” the F.A.O. expert said.
Nonetheless, Mr. Cressman said, the swarms are treatable.
“Treatment” means sabotaging the locusts’ advance. Relying on the expertise of ground trackers as well as satellite surveillance, international teams work together to predict a swarm’s path. The aim is to attack the locusts when they are most vulnerable.
In the late afternoon, when the swarm is close to settling for the night, the teams race after the locusts in an effort that Mr. Cressman compares to tornado chasing. Once they have landed in the desert, the team camps beside the swaths of insects. Then it waits for the morning’s first rays, when the coldblooded creatures, paralyzed by a chilly night, need to warm up before they can fly. That’s the opportune time to blast them with pesticide.
Alternatively, if a team catches a swarm in its infancy, it can home in on the younger locusts that cannot yet fly, known as hoppers. These form vast hopper bands that move in waves along the desert floor. “It’s like a moving carpet over the sand in the same direction, like someone’s leading them,” Mr. Cressman said. At that height they are easier to spray. Still, knowing how to control the flying swarms is considered the grander art.
The science of search-and-spray has shifted from a day when monitoring took place on camelback or on foot. Today the teams have tools like satellite surveillance, iPhone tracking, and vast data sets. Mr. Cressman can predict, for example, that once the locusts fly from Chad, they will hit North African countries like Libya in 10 days. That will complete a year’s cycle.
“This is the first time we had to face a situation where locusts developed in a place that was insecure – and then moved to a place that was insecure,” he said, referring to Libya and Mali. “It just so happened that this year the rains cooperated, too.”
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