Several West African countries are on alert for locusts. A swarm of the crop-eating insects has surfaced in Mauritania, where officials are working to prevent the locusts from breeding and spreading. The insects have ruined the harvest in several West African countries.

Locusts were sighted several weeks ago 250 kilometers northwest of Mauritania's capital, Nouakchott.

The U.N. Food and Agriculture Organization says it is closely tracking the insects as they move southward.

The FAO's locust forecasting officer, Keith Cressman, says the rainy season is a critical time to prevent the swarm from getting out of control.

"The rains have started in northwest Mauritania about six weeks ago. That is sufficient to allow the vegetation in the northwest to become green, and the soil to become moist," he said. "And these are the two conditions desert locusts need to reproduce."

Cressman says Mauritanian authorities will spray locust eggs with biopesticides. He says there should be enough supplies to handle the current infestation.

The FAO is sending a helicopter to monitor remote areas for new swarms. Survey teams in nearby countries, including Senegal, Mail, and Niger, are also watching for locusts.

In a single day, a locust can eat its weight in vegetation. The insects can mean disaster for farmers in a region that already has trouble growing enough food to feed its population.

Two years ago, locust swarms in Mauritania spread to neighboring countries during the peak of the harvest season, leaving millions in the region dependent on food aid.