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Carpenter ants are among the most commonly encountered structural pests in North America. Like all pests, however, they have a number of unique behavioral characteristics that are critical to understand for successful control. They include:

Carpenter ants move satellite colonies into buildings.

When you’re dealing with carpenter ants that are infesting a structure, you shouldn’t expect to find the main (mother) colony with the queen inside the building. In most cases, the main colony is outside, often living in a dead tree or stump. The ants that are causing a problem indoors are either just foraging inside in a search for food or water, or are living inside as members of one or more secondary, satellite colonies. Eliminating the satellite colony won’t necessarily eliminate the ant problem.

Carpenter ants prefer pre-softened wood for gallery construction. Start your inspection by looking for “conducive conditions.” Carpenter ants most often (but not always) start nest sites in wood that is damp, decaying or has been softened by a roof or plumbing leak, or by excess condensation. Even if the leak has been repaired, if the damaged wood remains, it is more vulnerable to attack. Check for dripping or standing water or stained or spongy, water-damaged wood. Ask your customer about leaks. Use a moisture meter and pay special attention to sites with readings higher than 20 percent. High-risk sites are laundry rooms, around dishwashers, around skylights, under shower or floor drains, or under bathtubs.

Carpenter ants often nest in small voids. Even though moist conditions are preferred, carpenter ants from satellite colonies will also move into dry, sound wood or even non-wood small voids. Typical void nest sites are inside curtain rods and hollow doors; behind kickplates; and in dresser drawers, hollow ceiling beams, false ceilings or foam insulation. In small voids, there is less need to excavate space for galleries.

Carpenter ant wood damage looks different than subterranean termite wood damage. You’d better know the difference between the two types of wood damage. However, sometimes both can be found together. Damage from either ants or termites is often not even visible on the outside surface of the wood, especially in early stages. If you break open the carpenter ant-infested wood, you should see wide, hollowed-out galleries that are clean and smooth, looking like they’ve been sandpapered. Unlike termites, carpenter ants don’t eat wood, so they don’t plaster their galleries with digested wood, there is no frass or fecal wood pellets, and the ants don’t bring in soil. The ants dump sawdust and debris out of their nest galleries, but you might find ant eggs or larvae in an active nest. Keep in mind that wood damage may not be from insects at all. Wood that is dark and mushy and crumbles can be damaged from wood rot instead.

Carpenter ants leave characteristic “dump piles.” Nest debris is pushed out of a nest through a slit-like opening in the wood or other existing opening. This garbage pile contains gouged-out wood pieces and sawdust, along with bits of debris or food: plaster, ant feces, sand, pieces of insulation and dead insects (both ants and prey). Dump contents vary with the material being excavated. The dump pile is usually directly beneath a nest site, but it is not always visible if the dump slit opens into a wall or other void instead. Termites do not leave a dump pile, and while wood-boring beetles push fine “sawdust” from their exit holes, it does not contain insect parts and debris.

Carpenter ants will travel more than 600 feet (180 m) in search of food. In warm weather, they forage from an outside colony mostly at night between 8 p.m. and 4 a.m. Carpenter ants are great trailing ants and will follow utility lines or tree branches to enter a structure. On the ground, they trail along natural edges of pavement, leaves, sidewalks or landscaping. They keep their trails clean and reuse them, eventually wearing a groove in grass or dirt. When occasional (non-winged) carpenter ants are seen indoors in warm weather, especially in areas with food, often they are foraging in from outside nests. Indoor ant trails are often found along the edges of floors, furniture or cabinets. At night, you may be able to follow trailing carpenter ants back to their nest whether from inside a structure or from their outside foraging trails.

Carpenter ants aren’t the only ants found infesting wood indoors. Most insects, including ants, prefer somewhat moist conditions. Several species of ants that can become indoor pests may end up nesting in decaying wood or termite- damaged wood. They may be confused with carpenter ants, although most are much smaller and not as dark. The larger yellow ant, odorous house ant, cornfield (moisture) ant, acrobat ant and little black ant are a few pest species that will nest indoors in moist wood. These ants don’t do much excavating but utilize existing galleries or voids in the wood.

The authors are well-known industry consultants and owners of Pinto & Associates.