Worker body colour is black, and there are strong hairs on the body. The legs are usually dark red.
Nests are established in damp or decaying wood; mature colonies contain 9,000 to 50,000 workers.
Colony. Egg laying is from April to June. Larval development is during the summer, with most of the workers produced by October. Egg production stops by August and September, and the larvae present in the colony overwinter with the queen. No food is consumed by the colony from October through January.
Habits. This is the dominant carpenter ant in the northwestern US. And adjacent areas in Canada. The satellite colonies of this species can be large, and from these they can move into and infest a nearby structure. Damage to structural wood can occur in a short time and is not limited to moisture—damaged wood. Satellite colonies in houses can contain several thousand ants. These ants typically maintain trails between the main colony and the satellites.