Monrovia  - Researchers have identified swarms of mystery caterpillars that have been devastating crops and polluting water in Liberia, raising hopes that the problem could be tackled.

Researchers on Tuesday said the pests were not army worms, as previously thought, but caterpillars of the moth Achaea Catocaloides.

The creatures emerged almost a month ago in the remote Bong, Lofa and Gbarpolu counties and were now threatening the food security of about 350,000 people.

Tens of thousands of people have already fled their homes as the caterpillars march across Liberia.

Agriculture experts warned that the worms, which are spreading rapidly and have already been sighted in Guinea, could spread into Ivory Coast and Ghana.

The United Nations Food and Agriculture Organization last week said 1.2 million dollars was needed to help combat the spreading swarm.

Samples of the caterpillars were sent to the Commonwealth Agriculture Bureau International and the International Institute of Tropical Agriculture in Nigeria for identification.

The caterpillar, which is normally not seen on such a large scale, has been known to attack cocoa crops.

It lays its eggs on the leaves of Dahoma trees. The young caterpillars eventually fall onto the ground, either pupating under fallen leaves if mature enough or marching off in search of more food.

Dr Winfred Hammond, a Food and Agricultural Organization entomologist, told the BBC that a spraying programme was the unavoidable next step.

"We cannot avoid applying pesticides," he said. "Now that we have an accurate identification, we can choose a pesticide which is specific to this species of caterpillar." (dpa)