By Richard Black
BBC science correspondent
The United Nations has warned of a serious shortfall of funds to combat locust swarms in north-west Africa as the insects spread to Chad.
A locust swarm can devour as much food as 1,000 people
More than $50m (£27m) is needed but less than half that amount has been made available, the UN Food and Agriculture Organisation said.
Locusts have landed in vast numbers in Mauritania, Mali, Senegal and Niger.
The organisation first warned last October that conditions were right for major swarms to develop this year.
Soon afterwards it appealed for funds to spray the early season breeding-grounds near the Atlas Mountains - action which could have prevented what nations further south are now experiencing.
The FAO believes that between $50m and $80m are needed in the coming months to control the insects but only around $10m has been received, with another $10m pledged.
Clive Elliott, senior officer of the FAO's locust group, said the insects were outstripping attempts to control them.
"The problem is that the international donor community is being pressed on all sides to help with different problems globally," he said.
"It takes a while for the penny to drop in terms of realising that the situation really is serious.
"Unfortunately the locusts get on with their reproduction and each generation they go through makes the problem worse."
Asia under threat
In Chad, swarms have been reported only 400km (249 miles) from the border with Sudan, where they threaten to add to the existing crisis in Darfur.
Major foods such as cassava and millet are being damaged, as are cash crops vital for export earnings.
Some farmers have chosen not to plant fields which would quickly be devoured.
In Mauritania, officials speak of 80% of the harvest gone and a million people at risk of famine.
The eventual extent of the damage depends largely on the weather.
The more it rains, the more the locusts will breed as they travel.
Most of the affected countries report that eggs have been laid and are already hatching and if swarms travel across Sudan they could eventually infest Iran, Pakistan and India.