Swarms of crop-devouring desert locusts are on the move and are likely to reach North Africa soon, the UN says.
A single locust can eat its own weight each day
Dense swarms of the insects have flown to Libya, and are heading for Morocco, Algeria and Tunisia, says the UN Food and Agriculture Organisation (FAO).
Up to four million hectares of land are estimated to be infested by locusts in countries across West Africa.
The swarms are moving north as their food in the semi-desert Sahel area runs out at the end of the rainy season.
"They move to greener pastures," the FAO's Keith Cressman told Reuters news agency.
He said the arrival of swarms in Libya was a warning to the rest of the region.
"It probably is the first sign of this shift in population."
So far, Mauritania has been worst affected, with thousands of farmers needing food aid after the locusts devoured their year's crops.
Mali, Niger and Senegal have also been badly hit.
But the FAO warns that the new swarms will begin to gather in the coming weeks as billions of new eggs hatch.
Several swarms of immature locusts had already invaded south-west Libya near Ghat and the Algerian border over the past week the FAO said in a statement.
The Senegalese village of Nande was invaded earlier this week.
"We cultivate for three months to feed our families for nine months," Mamousse Boulibe told Reuters, standing next to an almost bare field which was full of knee-high groundnut plants until clouds of pink locusts descended on it a few days ago.