Carpenter Ants

14 April 2008

Virginia Cooperative Extension, Charlottesville/Albemarle County Office
460 Stagecoach Road, Charlottesville, Virginia 22902
phone: 434.872.4580   fax: 434.872.4578

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It is about this time of year that folks start seeing insects wandering around inside their houses. One of the more noticeable of these insects is the carpenter ant.

Carpenter ants eating sugar.

These chunky black (sometimes red and black) ants can range from one-quarter inch for worker ants up to three-quarters of an inch for the queen. Like all species of ants, carpenter ants have a constricted hourglass waist and elbowed antennae. These characteristics distinguish them from the thick-waisted termites with their straight antennae. Ants are closely related to bees, wasps, and sawflies.

Carpenter ants share at least one annoying habit with termites. They construct extensive nests in wood, including logs, stumps, tree trunks, telephone poles, and, unfortunately, buildings. Nests are usually begun in deteriorating wood that has been exposed to moisture. Often, the colony will extend its nest to adjacent, sound wood.

The colonies of carpenter ants are often long lived. A single fertilized queen founds each colony. She establishes a nesting site in a cavity in wood. She then rears her first brood of workers, feeding them salivary secretions. She does not leave the nest nor feed herself throughout this period. The workers who are reared first assume the task of gathering food with which to feed the younger larvae. As the food supply becomes more constant, the colony population grows very rapidly. A colony does not reach maturity and become capable of producing young queens and males until it contains 2,000 or more workers. It may take a colony from three to six years or more to reach this stage. Each year thereafter, the colony will continue to produce winged queens and males, which leave their nest and conduct mating flights in the spring and summer.

While termites actually eat and digest wood, carpenter ants simply chew and tunnel through it to build their homes. Carpenter ants rarely cause structural damage to buildings, although they can cause significant damage over a period of years because nests are so long lived. Damage by carpenter ants can leave household structural timber open to fungus, rots, and other forms of decay. Some recent evidence indicates that they can also cause extensive damage to foam insulation. If faced with chewing through hard wood or soft insulation to build your nest, which would you choose?

Finding carpenter ants indoors in the winter is an indication that they are nesting somewhere within the walls or floors of the building. This is due to the fact that carpenter ants, like all insects, are cold blooded. Ants active in the winter must be originating from a warmed source. Even if the air temperature outside is very cold, heat from the sun or your furnace or wood stove may warm your house walls and stir overwintering ants to activity. Ants found in the spring and summer are often invaders wandering in from outdoors looking for food or drink. In the spring, carpenter ants go through a mass-mating or swarming behavior. During this time carpenter ants raid houses looking for sweets, because one of their normal sources of sugar, the sweet honeydew from aphids, is not available until the weather warms up.

The critical factor in carpenter ant control is treating the nesting area. Locating the nest site is very rarely easy and there are times it may be impossible to locate the nest. The most likely sources of carpenter ants are window and door frames and sills, shower and tub enclosure walls, and kitchen and bath plumbing walls.

One of the goals of Integrated Pest Management and one of the reasons we encourage carpenter control by direct nest treatment is to limit the amount of pesticide applied. Oftentimes, we can get the ants to help out with the treatment.

Their love of sweets can be their downfall. One of the most effective ways to control carpenter ants is to set out poison baits. Attracted to the sweet taste, the worker ants collect the bait and bring it back to the colony, where they share it with the developing larvae and the queen.

It can be important to know what kind of ant you are dealing with since some ant species prefer different foods. Baits are formulated to work with certain species and will most likely specify which ones on the label.

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For more information about this and other landscape topics contact your local Virginia Cooperative Extension office. The local Virginia Cooperative Extension office numbers are Albemarle 872-4580, Fluvanna 591-1950, Greene 985-5236, Louisa 540-967-3422, and Nelson 263-4035.