Countries in north and west Africa have been warned to be on alert for an outbreak of locusts, which devastated Mauritania two years ago.
A swarm of locusts can devour as much food as 2,500 people
Locusts had been found in Mauritania, and were laying eggs that were expected to hatch in the next 10 days, said the UN Food and Agriculture Organisation.
It warned Algeria, Mali, Morocco and Senegal to step up monitoring and to prepare to treat any outbreaks quickly.
"We are taking it very seriously," FAO official Keith Cressman told the BBC.
He said that while locust infestations were not uncommon in the area at this time of year, they must be dealt with or they could develop into the devastating swarms seen in 2004.
They swept across north and west Africa, leaving 60% of Mauritania's population - 400,000 people - needing food aid.
The FAO said the outbreak would offer the chance to test a new environmentally friendly pesticide which uses a natural fungus which kills locusts within one to three weeks.
Desert locusts breed rapidly, maturing in just three weeks, and are capable of travelling up to 100km (60 miles) a day.
Locusts can eat their own weight in food every day, which means a single swarm can consume as much food as several thousand people.