LIBERIA (Reuters) - A plague of hungry caterpillars known as army worms has eaten crops and plants in 100 Liberian villages and may spread across West Africa if left unchecked, the U.N. Food and Agriculture Organization said on Thursday.
Liberia, ravaged by a 14-year civil war that ended in 2003, declared a national state of emergency this week due to the army worms, a type of moth caterpillar which grows to 5 cm (2 inches) long and can swarm to destroy large swathes of vegetation.
Millions of the caterpillars have stripped fields and polluted wells and streams with their excrement in Bong County, northeast of Liberia's capital Monrovia.
The Rome-based FAO said six communities across the border in neighboring Guinea had already been hit by the army worms.
Large tracts of West Africa were at risk, it said, particularly when the caterpillars, now burrowing underground to form cocoons, emerged as adult moths.
"Each moth can fly up to 1,000 km (625 miles) -- and lay 1,000 eggs ... Potentially, that's a recipe for disaster," entomologist Winfred Hammond, the FAO's permanent representative in Liberia, said in a statement.
Army worms are known to eat cocoa plants, and neighboring Ivory Coast, the world's biggest grower, is already enduring a harvest blighted by disease and disorganization, though no sightings of the worms have been reported there or in Ghana, the second-largest cocoa producer.
Hordes of army worms had caused panic in some affected villages, over-running homes and causing residents to flee, the FAO said. About 500,000 people had been affected, it said.
Liberia declared a local state of emergency in Bong County and appealed for international help to contain the army worms nearly two weeks ago, when 19 villages had been affected.
But with many more villages now known to be infested, including some in nearby Lower Lofa and Gbarpolu counties, President Ellen Johnson Sirleaf declared a national state of emergency on Monday.
Government spray teams have started killing the caterpillars with insecticide, while food and water supplies are being distributed to the worst affected families.
The FAO said it was also considering using pheromone traps, using the scent of the female moth to lure males to their deaths.
Writing by Alistair Thomson; Editing by David Lewis and Sophie Hares