Carpenter Ants In Homes

Encyclopedia Article

 Carpenter ant
 Carpenter ant worker

Description of carpenter ants

Carpenter ants are very abundant in Iowa and are common pests in homes and other buildings.  The most common carpenter ants are the familiar “large, black ants” that are one-half inch or more in length and shiny black.  Other kinds of carpenter ants, however, are as small as one-quarter inch and are reddish-brown or two-toned.  One consistent characteristic of all carpenter ants is the smoothly rounded outline of the thorax when viewed from the side.  See the ISU website for an identification guide to common ants of Iowa. 

Carpenter ant life cycle and habits

Ants have a complete life cycle of 4 stages, Egg, Larva, Pupa, and Adult.  Also, ants are social insects that live in large colonies with overlapping generations and castes that perform different tasks. White, legless, grub-like larvae hatch from eggs laid by a reproductive female (queen). These are cared for by the workers (non-reproductive female adults). The larval stage lasts for approximately 3 weeks before transformation into a pupa. Carpenter ant pupae are encased in a silken cocoon.

Carpenter ants are scavengers. Although they are most active between dusk and dawn, ants can be seen during the day. Inside a house, carpenter ants feed on all food scraps, especially syrups, honey, jelly, sugar, meat, grease, and fat. Outside, they feed on honeydew, plant exudates, live or dead insects, and animal carcasses. Food is carried back to the nest by workers where it is shared with larvae, nonforaging workers and the queen.

Carpenter ant female with wings and 5/8 inch long body
Swarmer, queen. Winged female carpenter ant.

Swarming.  Ants with wings, called swarmers, may appear at times in the home.  Swarmers are ants that developed in their colony with wings (unlike the millions of wingless worker ants you usually see). Winged swarmers are sexually developed, male and female ants that serve as emissaries from a healthy, well-established colony. Swarmers depart from the established colony on a mission to initiate new colonies. They have very, very slim chances of success. Most will die of starvation, dehydration or will be eaten by birds, dragonflies, or other predators. Though almost all will fail, just enough succeed to spread the species and ensure its survival.  All species of ants are capable of producing swarmers.  Carpenter ant swarmers are recognized by their large size (body length of one-half inch or more).  For more about swarming behavior in ants, see

Damage caused by carpenter ants 

Carpenter ants do not eat wood but instead construct their nests in wood such as landscaping timbers, porch columns, windowsills, door and skylight frames, roofs, deck and fence posts, and structural lumber, especially moist, decaying wood.  Carpenter ants will also excavate soft materials such as foam insulation boards and may nest in existing cavities such as hollow core doors.  Nests are made by chewing an interconnecting series of tunnels and cavities. Wood is removed as coarse sawdust that is pushed from the nest. The sawdust may include other debris such as dead ants and parts of insects and other food. 

The galleries and nests of carpenter ants are large, irregular chambers. Unlike the nests of termites and wood-boring beetles, ant galleries are free of refuse and powdery wood and mostly free of sawdust. The walls of carpenter ant nests are usually smooth to the point of appearing to have been sandpapered.  Galleries do not follow the grain of the wood, unlike termite galleries.

Carpenter ants found indoors in the winter usually come from nests somewhere within the house.  Ants found indoors during spring or summer or on very warm days in winter could be invaders wandering in from outdoors, or they may be foragers from a nest in the wall or ceiling. While there is no easy way to determine the source, it does pay to check carefully before making any treatment.

Locating the source of carpenter ants is as important as it is difficult.  It is especially difficult if you see only a few ants at one time.  Our best suggestion is to spend time observing ants to see if you can detect a pattern of movement.  In spring and summer, carpenter ants are more active at night and observations after sunset, with a flashlight on the outside, and inside of the house may indicate the source.  The presence of sawdust is an important clue in locating carpenter ant nests.

Management of carpenter ants

Carpenter ant control can be a do-it-yourself project or a job for a professional pest control operator. Shop around and compare prices and services when selecting a pest control service.

Under ideal circumstances, the best carpenter ant control comes by locating and treating the nest (indoors or out).  Replace damaged or decayed wood and thoroughly seal the structure to eliminate future moisture problems.  The practical alternative indoors is to treat room edges, cracks and crevices in the areas where foraging workers are abundant and hope to reduce the population through the gradual elimination of the foragers.  Outdoor perimeter treatments with residual insecticide may also be useful.

OTC ant bait products that contain a sweet food may not eliminate carpenter ants.  However, specially formulated carpenter ant baits available to professional pest managers and have been very effective.  Place bait indoors where activity has been observed or is suspected.  Monitor bait and place more if it is consumed or remove it if there is no activity.  Outdoor granular baits may be effective when applied according to label directions.


Do you live in Iowa and have an insect you would like identified?

The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them.  Please see our website for current forms, fees, and instructions on preserving and mailing insects.   

Contact information for each states diagnostic laboratory for U.S. residents.  If you live outside of Iowa please do not submit a sample without contacting the Plant & Insect Diagnostic Clinic.  

Last Reviewed: 
July, 2020