Carpenter ants use wood as a nesting site and prefer wood that has a moisture content between 12% and 15%. And, although that seems like a restrictive limitation, they will adapt to much more humid conditions. The reason that they have earned the name carpenter ants has to do with the way in which they make the wood structure a nest. They tend to build galleries and trails within the wood, generally with the grain, and keep the galleries and paths neat and clean. They make entry into a home by finding wooden parts of the home that are in contact with the ground and hence, subject to moisture and rot. But, they can also gain entry where dead tree branches contact the home. Because they are neat and clean, they move sawdust and dead parts of other carpenter ants into side galleries or move it outside of the nest and make piles of wood and ant debris. The correct term for these accumulations is frass. It can be an indicator of ant activity but they can leave the frass in side galleries designated for waste.
Carpenter ants are omnivores and will forage both in the home, and outside looking for food. Like other ants, they leave pheromone trails to communicate with the ants from their colony. One interesting fact about these ants is that they can typically travel as far as 100 yards to find food. That is the distance of a football field!
I have been asked several times for a good source of information about carpenter ants and I finally found a complete guide to identification, habitat, location, and removal. The source is the University of Minnesota Extension service here.