By Pascale Harter
BBC correspondent in Nouakchott
Mauritania has repeated its call for urgent aid to combat the largest locust plague to hit West Africa in more than 20 years.
A locust swarm can devour as much food as 1,000 people
Aid agencies say the area may be on the brink of faminie, with donor countries only giving half the required funds to fight the locusts.
The centre for locust control in the capital Nouakchott says nearly half of some farmland is infested.
Farmers in the south say they can only afford to eat every other day.
Last week Mauritania's centre for locust control said it needed to spray 800,000 hectares of infested land. This week it has doubled its estimates.
Each day that money for pesticides and crop-spraying planes is delayed, locusts are multiplying in their millions.
After three years of drought, subsistence farmers in southern Mauritania say they are relying on this year's harvest.
So too are the billions of newly-hatched locusts, clearly visible around villages and farm land in the south, where it like stepping onto a moving carpet of hatchlings.
In three weeks' time crops are due to be harvested, just as the locusts are about to swarm.
Up to 40% of crops have been destroyed in some areas of Mauritania. Local officials are warning of famine.
Mauritanian officials say they need a further six planes and gallons more pesticide to curb the infestation
To stop the plague spreading to North Africa and across the continent to Sudan, the locusts need to be tackled now in Mauritania, Senegal and Mali.
But the United Nations' Food and Agriculture Organisation says it has still only received a tiny percentage of the $100m needed to fight this regional disaster.