Carpenter ants are a problem to humans because of their habit of nesting in houses. They do not eat wood, but they remove quantities of it to expand their nesting facilities. This can result in damage to buildings and, if the main structural beams are hollowed out, can result in an unsafe condition.

Most carpenter ant species establish their initial nest in decayed wood, but, once established, the ants extend their tunneling into sound wood and can do considerable damage to a structure. However, this damage occurs over 3 or more years, since the initial colony consists of a single queen. Workers are produced at a slow rate, so that a colony consisting of 200 to 300 workers is at least 2 to 4 years old.

These species commonly nest in standing trees (living or dead), in stumps, or in logs on the forest floor. Since many houses are being built in forested areas, well established, vigorous colonies are readily available in the immediate vicinity to attack these dwellings. This is especially true when the homeowner insists that the home be built with a minimal removal of trees.

A number of workers from these large “parent” colonies will frequently move into a dwelling as a “satellite” colony of this parent colony. Communication and travel between colonies is maintained, and the satellite colony may contain larvae, pupae, and winged reproductives. Since these colonies are already established, damage to houses can occur in a shorter time and is not limited to decayed wood. Indeed, these ants may become established in houses still under construction. The size of a typical colony is probably 10 to 20,000 workers, with large colonies having up to 100,000 workers. Not surprisingly, satellite colonies found in houses frequently contain up to several thousand workers.

The ants usually maintain a trail between the parent and satellite colonies. These trails follow natural contours and lines of least resistance and also frequently cut cross lawns. The trails are about 2 cm wide, and the ants keep them clear of vegetation and debris. Traffic on these trails may be noticeable during the day, but peak traffic occurs after sunset and continues throughout the night, sharply decreasing before sunrise. The parent colony is often located in a tree, stump, or in stacked wood within 100 meters of the house. Wood and stumps buried in the yard when the house was constructed or stumps and decorative wood pieces used to enhance the beauty of a yard or driveway may also be the source of a parent colony.

When workers vary in size, this is called polymorphism. The workers of some ants are monomorphic. Carpenter ants are polymorphic.

During the first warm days of spring-January-June, depending on locality- reproductives emerge from the nest for their mating flights. After mating the males die, the inseminated queen selects a nest site, usually in a small cavity in a stump, log, under bark, or in the timbers of houses. The queen then breaks off her wings along lines of predetermined weakness, and within a few days lays her first eggs. These soon hatch into larvae, which are fed by the queen from reserves within her body. The queen does not leave the nest to forage for food during the entire time she feeds and raises this brood.

At the end of their developmental period, the larvae pupate and eventually emerge as workers. Since these first workers have been fed only on the reserves within the queen’s body, they are very small and are called minors or minor workers. They usually number about 15 to 25. These workers then take over the functions of foraging for food, nest excavation, and brood rearing.

Once the colony is located, chemical treatment can provide excellent control. This consists of direct treatment of the colony and a perimeter spray against the foundation of the house (inside the foundation also, if the house has a crawl space instead of a basement).

Ants may also use a nearby tree to gain entry into the home via a bough or branch that is touching the structure. Tie back or remove such branches so this pathway will be unavailable to them.

Before houses are built in a forested area, the contractor may wish to consult an entomologist or pest control company to determine whether colonies of carpenter ants are located on the property. Colonies should be chemically controlled before construction begins.

Vegetation, particularly evergreens, should be planted and pruned so they are not in contact with the structure. This eliminates a foraging area for the colony as well as easy access to the structure.

Decorative bark, stumps, and driftwood brought into the yard for aesthetic effects frequently harbor colonies of carpenter ants or are a convenient site for colony establishment. This is also true of firewood piled high against the house. This is a poor practice and the wood should be stacked elsewhere.