Carpenter Ants

Order:  Hymentoptera
Family:  Formicidae
Scientific Name:  Camponotus pennsylvanicus (De Geer)

Carpenter Ants are ubiquitous pests found throughout North America.  Camponotus pennsylvanicus, the black carpenter ant, is the most common carpenter ant species found east of the Rocky Mountains.  Although worker ants are often seen searching for food and water, their importance as pests is based upon their invasion of structural wood for nesting sites.  Carpenter ants do not consume wood but excavate galleries in wooden timbers to create nests.

Biology and Habits

New colonies are initiated by fertilized females after the mating flight.  The female selects or excavates a small cavity in wood, seals the entrance hole and lays fifteen to twenty eggs.  The eggs are cream-colored, oval and up to 3 mm (1/8 in) in length.  The eggs hatch into tiny, legless larvae which are nourished by the queen.  When larval development is complete, the larvae spin cocoons.  After adult workers emerge from cocoons, they open the nest chamber and begin collecting food, enlarging and defending the nest, and caring for the larvae of future generations.  Under optimum conditions, development from egg to adult takes about two months, but may be extended during unfavorable conditions.

Adult workers, major and minor, vary in size (6 to 13 mm or ¼ to ½ in) and are distinguishable from other ant species by the presence of a single segment on the abdominal pedicel.  Other identifying characteristics are the presence of yellowish hairs on the abdomen and the evenly rounded profile of the upper side of the thorax.  Adult workers may be seen trailing to and from their nest, especially at night.  These ants must forage outside the nest for water and foodstuffs including plant and animal material, and honeydew produced by aphids on vegetation.

Older colonies (3 or more years) produce male and female reproductives referred to as swarmers or alates.  These winged forms emerge from the nest in the spring to early summer on warm, humid days.  Mating occurs and the males dies shortly thereafter.

Workers may initiate satellite nests (up to 5 or 6) by picking up and moving eggs and young larvae to suitable sites.  Although potential reproductives may be carried to the satellite nest, this type of nest lacks an egg-laying queen.

Control

In order to provide permanent relief from carpenter ant activity, the parent colony and satellite nests must be located.  Often, an indoor satellite nest is treated, but a brood from an untreated colony outdoors enters the structure and reestablishes the nest.

Common signs of ant activity include the presence of workers or swarmers, the accumulation of coarse sawdust with fragments of ant bodies, and scratching sounds produced by ants within their galleries.  Nests or colonies may be found indoors in hollow wall voids and door frames, galleries created by excavation of moisture-damaged wood, and in insulation.  Outdoors, inspect decaying wood including firewood, for activity.

Control of carpenter ants requires an integrated approach:  moisture elimination, removal of overhanging tree limbs, stumps and firewood, mechanical alterations and sanitation methods.  Place insecticidal treatments directly into the nest by drilling into inaccessible areas such as wall voids and applying a liquid or dust formulation.  Drill holes must be sealed after treatment.

Place residual treatments where nuisance foragers are seen.  Recent studies have shown that only a third of the workers will forage away from the nest, suggesting that this type of symptomatic treatment will only temporarily reduce the number of worker ants.  Fumigation is another option for control.

Generally, the most effective control is achieved through careful inspection by a trained, alert professional followed by focused insecticidal application.

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(Courtesy of the National Pest Control Association.)