Carpenter Ants are a problem to humans because of their habit of nesting in buildings. While they do not eat wood, they remove quantities of it to expand their nesting facilities. This can result in significant damage to buildings and even structural collapse. This damage occurs over three or more years since the single queen produces only 200 to 300 workers over a two to four year period.
In the Pacific Northwest, most problems are caused by the species known as Camponotus Modoc which commonly nest in standing trees (living or dead), stumps or logs on the forest floor. Buildings built in forested areas are prime targets of well established colonies. When the colony grows larger and needs room to expand or the old nest becomes less suitable, they expand to form satellite colonies. These satellite colonies are located in nearby structures.
The parent colony contains the queen, young larvae and workers, while the satellite contains the mature larvae, pupae, workers, and/or winged reproductives. The ants move back and forth from parent nest to satellite nest to feeding areas in nearby evergreen trees like Douglas fir, true fir and cedar. Sometimes they can be seen carrying mature larvae (white and grub-like) or pupae (papery cocoons).
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 across lawns. The trails are about 2 cm. wide, and the ants keep them clean 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.
Reproductive ants (winged males and females) leave the nest anytime from early January through June. Mating takes place in swarms from May to September. Mated queens find a suitable place to live, excavate a small home and begin laying eggs which become workers or queens. By the end of summer either workers have emerged or the larvae from late eggs become dormant. No feeding occurs during the winter months (November, December, January). The dormant phase ends about mid-January, when the queen begins laying eggs again.
Most carpenter ant workers are polymorphic which means they are different sizes. Entomologist refer to larger workers as "major" workers and the smaller workers as "minor" workers. Each colony has at least one queen that produces all members of the colony. There may be more than one queen in a colony.
When a colony gets very large (6 to 10 years old and has more than 2000 workers), it may produce winged reproductives, called swarmers. They are often produced during the summertime and may overwinter in the colony. The males often emerge first and are smaller than the females.
The diet of carpenter ants is quite varied and includes living and dead insects, honeydew from aphids, sweets, meat and fats. Workers leave the colony in late afternoon or early evening, forage during the night and return to the colony in the early morning hours. Carpenter ants carry food back to the nest intact or ingested and later feed it to non-foraging members in the nest.
Carpenter ants keep occupied galleries clean. They remove wood in the form of a coarse sawdust-like material, which they push from the nest. This often results in a cone-shaped pile accumulating just below the nest entrance hole. This pile may include, in addition to the wood fragments, other debris from the nest, including bits of soil, dead ants, parts of insects and remnants of other food they ate.
To prevent carpenter ant infestations, trim all trees and bushes so branches do not touch the house and correct moisture problems such as leaky roofs and plumbing. Paint and/or seal exposed wood construction before it becomes wet. Replace previously ant or termite-infested wood, rotted or water-damaged wooden parts of the structure and eliminate wood/soil contacts. Remove dead stumps on the property and store firewood off the ground and away from the structure. Stacks of firewood also attract carpenter ants. The longer wood remains undisturbed, the more likely it will become infested. It is better to keep on hand only the supply of firewood you plan to use during one heating season. Store the wood off the ground and away from the house. Spraying of firewood with pesticide to protect it is of little value and is not recommended.