Carpenter ants normally build their nests in hollow trees, logs, posts, landscaping timbers and wood used in homes and other structures. Unlike termites, ants do not feed on wood but excavate galleries in wood as places to build nests. Carpenter ants prefer to nest in moist or decayed wood, frequently entering existing cavities or void areas through cracks and crevices.
The ants usually cut galleries with the grain of the wood, following the softer parts. They leave the harder wood as walls separating the tunnels, but cut openings in these walls to connect the galleries. Access to the outside may be through natural openings, or the ants may cut openings where none exist.
Occupied galleries are kept very clean. Shredded wood fragments from the excavations are carried from the nest and placed outside. Cone-shaped piles of these fragments, often called frass piles, sometimes build up beneath the nest openings. Frass piles may also contain excretions, dead carpenter ants, and bits of wood, sand, soil or insulation. Frass is not always visible because ants may dispose of it in hollow parts of trees, in void areas in structures, or in unused galleries within the nest.
Carpenter ants become pests when they nest or forage for food in homes and other buildings. Usually, an infestation occurs when all or part of an existing colony moves into a house from outside. Ants enter structures through several common routes: where tree branches or utility lines contact a structure, through cracks and crevices around windows and in foundation walls, through ventilation openings in the attic, and through heating or air-conditioning ducts.