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Carpenter ants

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While often associated with wood that is dead or rotting, the carpenter ant is not the source of the deterioration, as is generally thought. Wood that is soft and moist is the carpenter ant’s preferred nesting site, and it is the telltale sawdust that is expelled during the construction of these nesting galleries that gives the insect its name. In reality, the underlying cause of the wood’s decay is probably a more serious problem than the ants themselves.

Reaching anywhere from 1/4 to 1/2 inch in length, the carpenter ant is one of the largest types of ants found in our area. Although the adult is usually black, some individuals can appear reddish or brown, with long yellow to grayish hairs on the abdomen. Carpenter ants have well-developed eyes, a constricted “waist,” and long antennae. The worker ant is wingless and outfitted with strong mandibles needed to excavate the nesting sites. The carpenter ant does not sting, but the larger workers can administer a sharp bite, which can become further irritated by the injection of an acid that they produce.

A social insect, carpenter ants live in colonies made up of a reproductive female or “queen”, males, workers, eggs, larvae, and pupae. The site of a colony can be determined not only by the discarded wood fragments deposited near the nest openings, but also by noticeable trails created when scouting ants go in search of food. These trails can run underground and may come to the surface some distance from the nest.

As a wood-nesting species, the carpenter ant will usually burrow its tunnel only a few feet off the ground, while the rest of the colony may live further up in the host tree. Eventually, the tunnels may strain the tree’s water-conducting capacity to the point where the tree becomes a hazard to nearby structures or passersby. There is usually a large “home” nest—most often located outdoors in rotting stumps and trees—and one or more satellite nests. It is the satellite nest that is often the source of ants found inside the home and any destruction of an indoor nesting site should also be followed up with a thorough examination of the surrounding outdoor area for the home nest. If the home nest is left intact, these ants can re-populate the area.

While there are some soil-nesting species, the carpenter ant prefers the softer wood associated with standing dead trees and stumps. Overpopulation, however, will cause them to search for new nesting sites, with nests often being created in the interior of living trees such as sugar maple, sweetgum, cherry, peach, plum, almond, northern white cedar, and balsam fir. They can gain access through cracks, wounds, knots, or any decayed or faulty place on the tree’s exterior.

Carpenter ants are also attracted to any decaying or damaged structural wood—from discarded construction materials to telephone and power poles—or to any site in a building where wood has been allowed to rot due to water damage. Homeowners should pay particular attention to high-moisture areas such as bathrooms, laundry areas, and basements, and conduct routine examinations for leaks in and around roofs, gutters, chimneys, and windows.

A nocturnal insect, the carpenter ant prefers to stay out of direct sunlight and is most often seen during its nighttime foraging excursions. The scouting ants will lay down a pheromone trail from the nest to the food source for the rest of the colony to follow. Carpenter ants feed mostly on dead and living insects and the honeydew emitted by aphids or other sap-sucking insects. They also have a fondness for the juices of ripe fruits and grains of sugar or other sweets. This is usually what draws them inside the home.


Due to their preference for sweets, juices, and fats, proper food storage and sanitation is an important step in eliminating the carpenter ant as a household pest. Do not leave dirty dishes or food in exposed areas. Washing areas with a detergent solution where ants are seen foraging may reduce or eliminate the pheromone scent. Conduct a careful examination of all structural areas for signs of water damage or wood rot. Replace soft wood and caulk all exterior openings. Remove vegetation debris from around all buildings. Do not place firewood directly on the ground and store it away from the house. If possible, cover the wood so rainwater cannot soak into it. Keep areas next to basement walls as dry as possible and provide proper air circulation or ventilation in areas subject to dampness.


For indoor applications: ant baits or other ready-to-use insect sprays are effective for use around baseboards and doorways and in any cracks and crevices in non-food areas where ants may travel. Contact the Plant Clinic (630-719-2424 or for current recommendations. Use pesticides safely and wisely; read and follow label directions. The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.