The black carpenter ant, Camponotus pennsylvanicus (DeGreer), is a native species and the common species in the east. The western black carpenter ant, Camponotus modoc Wheeler, and C. vicinus Mayr are the common western species. In Hawaii, the serious pest is the Hawaiian carpenter ant, C. variegattus (Fr. Smith), a species introduced from southeastern Asia. These ants get their common name from their habit of hollowing out galleries in pieces of wood for nesting purposes. This nesting habit can result in structural damage. Carpenter ants are found throughout the United States.
Workers polymorphic, large (1/8-1/2" or 3.5-13 mm) but vary greatly in size; queens about 1/2-5/8" (13-17 mm) long. Color black, combinations of red and black, or completely red or brown. Antenna 12-segmented, without a club. Thorax lacks spines, profile evenly rounded on upper side. Pedicel 1-segmented. Gaster with anal opening round, surrounded by circlet of hairs. Stinger absent. Workers capable of emitting a strong formic acid odor.
Camponotus pennsylvanicus with workers about 1/4-1/2" (6-13 mm) long and completely black except top of gaster with long, pale yellowish hairs pressed against its surface. Camponotus modoc with workers about 1/4-1/2" (5-11 mm) long, dull black with reddish legs and with golden hairs covering abdomen. Queens up to 5/8+" (17+ mm) long. Other species black, various combinations of red and black (e.g., C. vicinus), or completely red or brown. Although carpenter ants do not sting, their bites can be quite painful, especially when they inject formic acid into the wound.
(1) Dark field (Formica spp.), larger yellow (Acanthomyops interjectus), and Allegheny mound (F. exsectoides) ants have profile of thorax not evenly rounded, with distinct impression(s); in addition dark field ants with front and hind margins of node steeply or equally sloped.
(2) Velvety tree ants (Liometopum spp.) lack circular anal opening surrounded by circlet of hairs.
(3) Other medium to large dark ants with 2-segmented pedicel.
The only external indication of infestation other than the presence of workers and/or swarmers is the appearance of small openings or windows on the surface of the wood. Through these, the workers expel debris which consists of sawdust-like shavings and/or fragments of insulation and insect body parts. The accumulation of such debris below such holes is a good indication of an infestation.
Inside, the galleries follow the softer spring wood with numerous connections through the harder/dark summer wood. The gallery walls are smooth, with a sand-papered appearance. The active galleries are kept clean of debris.
They prefer to attack wood softened by fungus and are often associated with moisture problems.
Black carpenter ant colonies are of moderate size, usually containing over 3,000 workers (up to 10-15,000 including satellite nests) when maturity is reached in about 3 to 6 years. The typical black western carpenter ant (C. modoc) mature colony contains about 10-20,000 workers, with large colonies of more than 50,000 workers. There is usually only one functional, wingless queen per colony. However, colonies of C. vicinus are multiqueened, with as many as 40 queens reported in a single nest, and have huge colonies of over 100,000 workers. Swarmers are not produced until the colony is more than 2 years old, usually 3.5-4 years old for C. pennsylvanicus and often 6-10 years old for C. modoc. They are produced in the previous year and held over the winter in the nest for release the next year. Swarmers appear from May until August in the east and from February through June in the west. The western black carpenter ant usually swarms in the late afternoon to early evening on sunny, warm, humid days. Mating typically occurs during swarming. The males die shortly after mating. The inseminated females break off their wings and seek a nest site.
The first clutch of eggs numbers 9-16. They hatch in 2-5 weeks, depending on the species and temperature. The queen feeds her first clutch primarily by metabolizing her body fat and flight muscles. The hook-shaped larvae go through 4 instars in 2-3 weeks. The prepupal and pupal stages last 2-4 weeks. The queen must assist the emerging adults in freeing themselves from their cocoons. Developmental time (egg to adult) for workers takes 6-12 weeks. Workers are polymorphic, with majors, minors (minims) and intermediates present.
Most carpenter ant species establish their first nest in decayed wood and later expand or enlarge this into sound wood. Inside, nests are located in wood (preferably softened by fungus rot), in insulation, and/or in wall voids. Workers are a nuisance when out searching for food but are destructive to timbers utilized for nesting activities. Outside, nests are typically located in rotting fence posts, stumps, old firewood, dead portions of standing trees, and under stones or fallen logs.
Outside is the usual location of the parent colony, where the queen, eggs, and young are located. In mid-summer, satellite nests, which contain workers, mature larvae, and pupae, are established either outside or indoors. Usually around August, workers and winged males and females emerge from these pupae. The winged forms are held in the nest until the time to swarm the following spring. The intervening 9-10 months allows the female ovarioles (ovaries and associated tubes) to mature. It’s the winged males that test environmental conditions and determine if it’s time to swarm. If conditions are right, the males release a pheromone that stimulates the females to leave the nest. However, since indoor nests are typically in warmer conditions than their outside counterparts, males will sometimes come out and test conditions several times before it’s time to swarm. The first appearance of winged males often causes great concern by the residents because it is often their first hint that ants are living in their house. Otherwise, the presence of a carpenter ant nest indoors is sometimes indicated by a rustling sound that will come from wall voids or from wood where the nest is located when the winged forms are disturbed. Carpenter ants feed primarily on insect honeydew, plant and fruit juices, insects, and other arthropods. Inside, they will also feed on sweets, eggs, meats, cakes, and grease. The workers forage for distances of up to 300 feet (91.4m) from the nest. They typically enter buildings around door and window frames, eaves, plumbing and utility lines, and shrub and tree branches in contact with the building. Although some workers are active during the day, most activity is from dusk till dawn, with peak activity between 10 pm and 2 am. The trail between the parent and satellite nest is usually about 1/4-13/16" (6-20 mm) wide and is kept clear of vegetation and debris. It usually follows contours but typically will cut across lawns.