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USDA United States Department of Agriculture
Prepared by Forest Service Alaska Region
Leaflet R10-TP-128
April 2004

Carpenter Ants: Insect Pests of Wood Products
Carpenter ants, Camponotus spp. (Hymenoptera: Formicidae), are among the largest members of the ant family in the United States. Under natural conditions, nests can be found in rotting logs, stumps, or occasionally in damp heartwood of live trees. However, they may also construct their nests in house timbers or other manmade structures where wood becomes moist. Occasionally, they are found tunneling into Styrofoam insulation. Well-established ant colonies may cause structural damage in homes requiring extensive repairs. Carpenter ants are also a nuisance when invading homes, crawling over kitchen surfaces and getting into food.

Carpenter ants may be active indoors during spring and summer foraging for food where the favored foods are sweet or fatty fare such as syrup or other domestic foods. If these are not available, the ants will feed on dead or living insects or other types of organic material. If more than 20 ants are found in a home, especially in the winter months, the infestation is most likely within the home and needs to be treated.

[image: Tree damaged by carpenter ants with inset close-up of carpenter ant]

Description and Life History
Carpenter ants are social insects and live in colonies made up of three castes: (1) "swarmers", winged females, up to 3/4-inch long, and much smaller winged males; (2) a wingless queen, which never leaves the nest and spends her entire life laying eggs; and (3) workers, of which there are major workers, about 1/2—inch long, that guard the colony and forage for food, and minor workers, 1/4—inch long, that care for the queen, eggs, and developing larvae.

Queens are generally black while workers will either have some red or brown on their legs or body. Carpenter ants have a smoothly rounded arched shape to the top of the thorax, elbowed antennae, and constricted waists with a single node between the thoraxand abdomen. Workers have a large head and small thorax, while swarmers have a smaller head and larger thorax to accommodate flight muscles. Swarmer wings are long, with the forewing longer than the hindwing, clear or brownish
with prominent veins (Figure 1).

[image: Figure 1. Winged female and a much smaller male carpenter ant].

Swarmers emerge from mature colonies usually in May and June. Males die after mating but the newly fertilized females, which are mated for life, either reestablish an
old colony or establish a new satellite colony in a small cavity in down logs or stumps or in deteriorating moist wood. The new queen loses her wings and lays 15 to
20 eggs over the next 15 days. Eggs are about 1/8—inch long, oval, and cream colored.

Eggs hatch after 24 days and the larvae emerge. Larvae are legless and grub-like with their size varying according to their ultimate adult form (i.e. swarmer, worker, etc.). Larvae pupate in tough, tan-colored, silken cocoons often erroneously referred to as "ant eggs." The larval stage is usually completed in 21 days and the pupal stage completed 21 days later. However, cold winter weather may delay the life cycle.

All eggs produced in the first three years become sterile female workers. These workers assume the duties of collecting food, feeding the queen, excavating galleries to enlarge the nest, and tending the eggs, larvae, and pupae of the next generation. Workers are able to forage for food up to 200 yards from the nest and although they do not sting, their bite can be painful. Colonies mature and begin to produce swarmers in three to six years. A mature colony has 2,000 to 4,000 individuals and will produce 200 to 400 winged swarmers each year. There is normally only one functioning wingless queen in a colony, and she generally lives and produces young for up to 15 years.

Damage Caused
Carpenter ants do not eat wood, but excavate galleries to rear their young preferring moist (not wet), deteriorating wood that may be found in existing cavities or void areas in structures. Nests are commonly found in porch pillars, roofs, windowsills, and structural wood in contact with soil. Workers cut galleries in the wood, often extending into adjacent sound wood, expanding the nest size for the enlarging colony. Galleries are irregular, usually excavated with the wood grain (Figure 2); the walls are smooth and clean with shredded wood fragments (frass) deposited outside of the nest.

All kinds of houses, from the newest to the oldest, may become infested. In cities, carpenter ants are usually found in wooded areas, but may also be found in crowded
residential districts as well.

Guidelines for Reducing Damage
The most obvious sign of infestation is the presence of ants inside the house, especially in winter. Carpenter ants may remain active year-round in heated spaces,
otherwise they become inactive in the winter. Other indications of infestation include piles of the sawdust-like frass expelled from small cracks or openings found in
dark closets, under porches, along sills, or at the base of infested timbers (Figure 3). Carpenter ant frass can be distinguished from regular sawdust by the presence of
fragments of ants and other insects mixed with the wood debris.

Prevention is the best control method; measures to prevent structural timbers from becoming wet may protect a house from infestation. Building sites and adjacent areas
should be cleared of stumps and partially decayed logs. If possible, buildings should be positioned on concrete or masonry foundations or on treated timbers. Lumber, firewood, and debris should not be stored nex tto the house or in basements and crawl spaces. Food, including pet food, should be kept in sealed containers.

[image: Figure 3. Frass piles are evidence of carpenter ants.]


The most important factor in carpenter ant control is locating the nest. Once the nest is found, control may be easy. Sometimes more than one colony is present in a structure or surrounding grounds, so a thorough inspection is very important. Once the nest is located, infested wood can be removed or chemically treated and the causes of moisture damage can be corrected.

Check with your local Cooperative Extension Service office for insecticides that are currently registered for carpenter ant control.

Photography Credits
Cover photo: E. Holsten, USDA Forest Service, www.insectimages.org
Figure 1: W. Cranshaw, Colorado State University, www.insectimages.org
Figure 2: R. Werner, USDA Forest Service, www. insectimages.org
Figure 3: E. Holsten, USDA Forest Service, www. insectimages.org

Caution: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish or other wildlife—if they are not handled or applied
properly. Use all pesticides selectively and carefully. Since approved uses of a pesticide may change frequently, it is important to check the label for current approved
and legal use.

Follow recommended practices for the disposal of surplus pesticides and pesticide containers. Mention of a pesticide in this publication does not constitute a
recommendation for use by the USDA, nor does it imply registration of a product under Federal Insecticide, Fungicide, and Rodenticide Act, as amended. Mention of a
proprietary product does not constitute an endorsement by the USDA.

Carpenter Ants
Original 1982, Ed Holsten, Research Entomologist, USDA Forest Service, Alaska Region, State and Private Forestry. Revision 2004, Cynthia Snyder (M. Sc.), Biological Technician, USDA Forest Service, Alaska Region, State and Private Forestry.

Additional information on this insect can be obtained from your local
USDA Alaska Cooperative Extension office, Alaska State Forestry office, or from:
Forest Health Protection, State & Private Forestry
USDA Forest Service
3301 C Street, Suite 202
Anchorage, Alaska 99503-3956
Phone: (907) 743-9455

Forest Health Protection, State & Private Forestry
USDA Forest Service
2770 Sherwood Lane, Suite 2A
Juneau, Alaska 99801-8545
Phone: (907) 586-8883
or: http://www.fs.fed.us/r10/spf/fhp/

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, sex, religion,
age, disability, political beliefs, sexual orientation, or marital or family status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require
alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA's TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326-W, Whitten Building, 1400 Independence Avenue, SW, Washington, DC 20250-9410, or call (202) 720-5964 (voice and TDD). USDA is an equal opportunity provider and employer.

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