Liberian crop pest mystery solved

A mystery pest which has devoured crops and contaminated water in Liberia and Guinea has finally been identified.

The insects, thought to be armyworms, are in fact the caterpillars of the moth Achaea catocaloides, says the UN's Food and Agriculture Organization.

Cornering the culprit will allow the government to select the best pesticide to tackle the outbreak - the worst seen in Liberia since 1970.

More than 20,000 people have so far had to evacuate their homes.

As well as devouring coffee, cocoa and plantain crops, the invaders have polluted drinking water sources with their faeces.