Carpenter Ants

Carpenter ants are social insects that live in colonies, primarily in wood. They hollow out wood to build their nests, making their galleries and chambers velvety-smooth as if a carpenter had sanded the surfaces. Their tunneling in wood and foraging for food and water lead to their �pest� status in or around homes. Carpenter ants are an excellent indicator of moisture problems in a building, or other conditions conducive to their infestation, such as rotting wood, that need attention.


Homeowners can minimize damage to their houses from carpenter ants by learning how to identify the ants, knowing their nest site preferences, and taking proper preventive and control measures.


Carpenter ants normally build their nests in hollow trees, logs, posts, landscaping timbers and wood used in homes and other structures. Unlike termites, they do not feed on wood but merely use it as a place in which to build a nest. They prefer moist or partially 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. They cut openings in these walls to interconnect the galleries. Access to the outside may be through natural openings, or the ants may cut openings where none exist naturally.

Occupied galleries are kept immaculate. Shredded wood fragments from the excavations are carried from the nest and deposited outside. Cone-shaped piles of these fragments sometimes build up beneath the �windows� or other nest openings. The piles may also contain inedible parts of insects from their diet, bits of sand or soil, dead ant bodies from the colony, and gener-al debris. This �sawdust� or �frass� is not always visible, because ants may dispose of it in hollow parts of trees, void areas in structures, or unused galleries in the nest.

Carpenter ants become pests when they nest in one of the voids or damp areas in human construction, or when they forage for food in our houses. Usually, an infestation occurs when all or part of an existing colony moves into a house from outside. Ants can enter when 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 foundation heating or air conditioning ducts.

They usually nest in wood that is very moist or previously damaged by water or termites. A colony develops best in wood with moisture content above 12 to 15 percent. This requires the wood to be wet by rain, leaks, condensation or high continuous relative humidity. Typical locations include

  • Wood affected by water seepage from plugged drain gutters, damaged flashing, wood shingle roofs, poorly fitted or damaged siding, improper pitch of porch floors, between the roof and ceiling of flat deck porches, hollow porch posts and columns, or leaking door and window frames;
  • Areas around plumbing in kitchens and bathrooms where water leaks have occurred, soaking the surrounding wood;
  • Wood in contact with soil, such as porch supports, siding and stair risers;
  • Wood in areas of poor ventilation or condensation such as cellars, crawl spaces, attics or under porches;
  • Wood debris in dirt-filled slab porches;
  • Voids under bathtubs or hot tubs;
  • Hollow wooden doors, hollow ceiling beams, hollow shower and curtain rods;
  • Sill plates and floor joists;
  • Voids under attic insulation or under insulation in crawl spaces; and
  • Voids above windows, doors and bay windows.



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