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. Government officials and international experts are searching for a strategy to control the outbreak, which threatens to spread because first -generation Achaea caterpillars are dropping to the ground and turning into pupae, then moths.