Carpenter Ants

Carpenter Ants

carpenter ants

Carpenter ants are social insects that live in colonies, primarily in wood. They use their mouthparts like tiny wood chisels to hollow out wood to build their nests. Because they often forage for food and water inside the home, most people see them as a nuisance. But, carpenter ants can also be an indicator of moisture problems or rotting wood that needs attention.

Identification

Queen Carpenter AntThere are two carpenter ants found in Nebraska. Black carpenter ants are large, black ants. Adults vary in length from 1/4- to 3/8-inch. The queen is 1/2-inch long and is the largest ant in Nebraska. There is a second carpenter ant in Nebraska that is a smaller, about 1/4-inch. We call it the "red" carpenter ant to distinguish it from the black carpenter ant, but it is really two-toned. The thorax is reddish brown, while the head and abdomen are darker.

The months of February and March seem too early for insects, but it is not uncommon for people to see carpenter ants indoors during these months. Sometimes they find winged ants which are the colony's reproductives, the queens and kings. When colonies are in outdoor locations, the mated queens fly off to start new colonies. When there are winged carpenter ants in the house, there is most likely a colony living within the structure.

People also see carpenter ants inside the home when foraging workers from an outdoor colony enter the house looking for food. Carpenter ants forage on a wide variety of food items and often are found in the kitchen where they are attracted to moisture. When you see foraging ants, there is no way to know for sure if the colony is outdoors or indoors. More investigation is needed.

Nesting sites

Carpenter ants normally build their nests outdoors in hollow trees, logs, posts, and landscaping timbers. 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.

Occupied galleries are kept immaculately clean. Ants push sawdust out of the nest to keep it clean; piles of sawdust underneath the nest are a sign of a colony. This sawdust is not always visible, because colonies can be hidden in wall voids.

Carpenter ants nest inside our house structure when wood is very moist or has been 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 interior nest 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 or behind poorly grouted tiles;
  • Wood in contact with soil, such as porch supports, siding, and stair risers;
  • Wood in areas of poor ventilation or condensation such as cellars, crawlspaces, attics, or under porches;
  • Wood scraps in dirt-filled slab porches;
  • Voids under bathtubs or hot tubs;
  • Hollow wooden doors and ceiling beams;
  • Sill plates and floor joists;
  • Voids under attic insulation or under insulation in crawlspaces;
  • Voids above or below windows.

Management

The key to successfully managing carpenter ants is find the colony. Inspect the structure thoroughly, both inside and out. Carefully examine the areas listed above for signs of carpenter ants. Conical piles of finely shredded sawdust are indicators of nest sites. Eliminating a carpenter ant colony can be difficult for the homeowner-especially when the colony is hidden inside a wall. Because of the association between moisture and carpenter ants, eliminating the source of the moisture often controls the colony without the use of insecticides.

Tips to prevent carpenter ants include:

  • Repair plumbing or roof leaks promptly and replace damaged wood;
  • Make sure there is proper clearance between soil and structural wood;
  • Provide good ventilation under the house and in the attic;
  • Drain water away from the structure;
  • Remove stumps, logs and wood debris near the house;
  • Store firewood away from the house;
  • Trim back any tree or shrub limbs touching the structure;
  • Keep exposed wood in good condition, with all cracks, knot holes, checks, or joints properly sealed with wood putty, and all surfaces painted.

Insecticide Treatments

Over-the-counter (OTC) "ant sprays" are rarely effective. Some ants will be killed but these OTC products will not kill the colony. More effective treatments include insecticidal dust treatments in wall voids. Another effective method is a perimeter treatment using is an insecticide that foraging ants pick up and transfer to other members of colony. The active ingredient fipronil has been shown to transfer through colonies and the product Termidor is labeled for this use. It is a professional-use product and not available to do-it-yourselfers. It is labeled for outdoor use only and can only be used twice each year.

If you see ants and are unsure whether they are carpenter ants, you can have them identified by bringing them to your local extension office.

Barb Ogg
Emeritus Extension Educator, Entomology
Barb Ogg shared her love of entomology with clientele throughout Nebraska for many years through Nebraska Extension. Barb retired in 2015.

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