Carpenter Ants produce small piles of what look like coarse black pepper. They can do as much damage as termites, but are fortunately easier to eradicate, because unlike termites, they come out to forage like regular ants, and only burrow to make nests in the walls. If you've seen ants crawling about, this is probably the problem. To get rid of them you will want to use a slow acting poison that they can take back to the nest so they get the whole colony. Regular insecticides only kill the ones you see. Look for permethrin or fipronil based poisons. The chemical names will be written on the packages. Don't bother with boric acid as it doesn't track back to the nest.