for National Geographic News
They came by the millions out of the forest.
From off in the bush, townspeople at the epicenter of the plague heard a low roar, like the sound of heavy rain cascading down through the leaves. It was caterpillar droppings.
In early January, when the long, black caterpillars reached the creeks that serve as the main water sources for the town of Belefanai in north-central Liberia, the creatures' feces instantly turned streams dark and undrinkable.
Moving through the forest canopy on webs, devouring the leaves as they went, the caterpillars advanced like nothing the townspeople had ever seen.
They ate food and cash crops—coffee, cocoa, citrus, plantain, banana, and cassava. They took over homes and people fled.
Venturing into the forest meant being hit by a wave of caterpillars that appeared to be moving forward about as fast as the average person walks.
"The worms would drop on you from all angles," said Moses M. Kolinmore, a mason who arrived in Belefanai just as townspeople realized they had to get word to the government.
"They would cover the whole ground—thousands upon thousands of thick, strong, stubborn worms. It was fearful, very fearful."
The outbreak, which began in December in a remote, forested region of Guinea just over the border from Belefanai, has affected an estimated half million people in more than a hundred towns and villages, prompting the Liberian government to declare a state of emergency.
This week entomologists identified the insect as a moth with a name only scientists had heard before: Achaea catocaloides.
A New Pestilence
The caterpillar is not, as first suspected, the African army worm, a creature well-known for infesting huge regions of East Africa.
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