The U.N. Food and Agriculture Organization says experts are in a ?race against time? to stop a ?vast plague? of Armyworm caterpillars in Liberia. The Liberian government on Monday declared the infestation a national emergency.

As the Armyworms continue their march, they devour vegetation and pollute wells and streams with excrement. If their advance in north and central Liberia is not stopped soon, other West African countries could soon be at risk.

Experts from the FAO and other agencies are still trying to determine to best course of action to stop the Armyworms. Winfred Hammond, the FAO?s permanent representative in Liberia, says they first have to determine the exact species of the pest.

?The exact species is yet to be determined because it?s easier to do that with adults and we?re beginning to have some adults emerging. So we can get that confirmed very soon. It is important with Armyworms to be sure about the species because you may be depending on pheromone traps and things like that for their control,? he says.

 The pheromone traps use hormones to attract the pests once they become moths. But specific pheromones must be used for a particular species, otherwise the traps won?t work. That?s why the species must be identified.

?Those pheromone traps perform two functions. They help you detect the presence (of the Armyworms), but they also help you to attract them to one spot where you can easily kill them with pesticides, safer pesticides. You don?t want to spray indiscriminately pesticides all over the place. You want to target the pest,? he says.

Introducing viruses, bacteria and fungus into the Armyworm population can also help control the pests. In the meantime, Hammond says the Armyworms are spreading rapidly.

?There are reports 106 villages have now been affected. It has gone from about 46 villages about a week or so ago to now 106 towns and villages. We also have confirmed reports that Guinea-Conakry ? that two towns about 25 kilometers from the Liberian border have also been infected,? he says.

Hammond says that it?s currently the dry season in north and central Liberia so there are few crops in the field for the Armyworms to eat. But if they?re able to launch, what?s called, a secondary infestation, new Armyworms may emerge just in time to eat new crops.

One female can lay as many as one thousand eggs in seven days. When they evolve into moths, nature determines what happens next.

?They move in different directions depending on the wind direction and also on the speed of wind. They could go as far as a thousand kilometers from the spot where they were breeding. And then you could have in the same place a secondary infestation or new source of infestation in another country altogether,? he says.

The FAO official says experts hope to know within three or four days how and when they can control the problem.