"Carpenter ant species reside both outdoors and indoors in moist, decaying or hollow wood. They can leave a sawdust-like material behind called frass that provides clues to their nesting location. Certain parts of a house, such as around and under windows, roof eaves, decks and porches, are more likely to be infested by Carpenter Ants because these areas are most vulnerable to moisture."[1]
[1] Wikipedia