On this page
How to identify it
- Among the largest ants in North America: workers are about 1/4 to 1/2 inch long, black or red and black depending on species; winged reproductives can reach 3/4 inch.[1][2]
- Sizes vary by source and species: Minnesota says workers are usually 3/8 to 1/2 inch (one species is only 3/16 inch) and queens can reach an inch, while Clemson says the larger workers run 1/4 to 5/8 inch, winged females up to 3/4 inch and males under 1/2 inch. Workers of the same species come in different sizes.[4][5]
- One node at the narrow waist and an evenly rounded back when viewed from the side.[1][4]
- Elbowed antennae and, on winged forms, front wings longer than hind wings, unlike termites.[1][2][4]
- Sawdust pushed from nests is coarse and fibrous, often mixed with insect parts, unlike the six-sided pellets of drywood termites.[1][2][5][4]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Termites (winged) | Termites have a broad waist, straight beadlike antennae and front and hind wings of equal length; carpenter ant galleries are smooth and clean, without soil or fecal pellets. Minnesota adds that termite workers are light-colored and rarely seen outside their colony.[1][2][4] |
Where it lives
Common wherever there are shade trees, especially in wooded and foothill communities. Parent colonies nest in live or dead trees, stumps, logs, woodpiles and landscape timbers, often within 100 yards of the house, with satellite nests in buildings.[1][2]
Biology and life cycle
Colonies grow slowly; only after several years do they produce winged males and queens, which fly in spring or early summer to mate and start new colonies.[1][2]
Clemson says a colony starts satellite colonies once it is six to ten years old and has more than 2,000 workers. Penn State says 200 to 400 winged ants develop in summer, stay in the nest through winter and leave the next spring or early summer.[5][2]
Workers forage mostly at night, feeding on insects, honeydew from aphids and scales, nectar and fruit juices, and indoors on sweets, meats and fats. Minnesota says they search for food between sunset and midnight in spring and summer, sometimes up to 100 yards from the nest.[1][2][4]
Only about 10% of the ants are out foraging at any one time.[1][4]
Their tastes shift with the season: Clemson says they favor protein in spring and sweets in winter, and Minnesota suggests tuna packed in water as a spring lure.[5][4]
Satellite nests hold workers, pupae and mature larvae but no eggs or queen, so Minnesota says they can be in fairly dry spots such as insulation, hollow doors, sound wood and wall voids. Penn State, by contrast, says the ants seldom tunnel into dry, sound wood.[4][5][2]
Carpenter ants belong to a stingless ant subfamily whose venom was long thought to be just formic acid. A 2026 study of eight species found 35 venom peptides as well, some of which fight fungi and may help keep the colony clean.[6]
Damage and signs
- Indoors they nest in wall voids, hollow doors, insulation, window and door casings, sills, joists and porch timbers, especially where wood is wet from leaks, condensation or poor ventilation. Minnesota lists spots behind bathroom tiles, around tubs, sinks, showers and dishwashers, under roofing and subfloor insulation, and inside foam insulation.[1][2][4]
- Large colonies can extend galleries from decayed wood into sound wood and weaken it, though Penn State notes that in homes they usually nest in hollow spaces and rarely cause major structural damage. Minnesota says the longer a colony is present the more damage it does, but damage usually builds slowly, often over years, and Clemson calls them a serious structural pest across the southeastern United States.[1][2][4][5]
- Signs include piles of coarse wood shavings and insect parts below cracks and moldings, and a faint rustling in walls. Minnesota says the rustling gets louder if the colony is disturbed, and steady indoor sightings of 20 or more workers also point to a nest.[1][2][4]
- Their galleries are clean and smooth, with a sanded look, and often run across the grain.[4][5]
Health risk
Carpenter ants have no stinger. They defend themselves by biting with strong jaws and can spray formic acid into the wound; they belong to the stingless ant subfamily whose venom is based on formic acid.[1][6]
Control
Prevention
Fix the moisture: repair leaking roofs, gutters, flashing and pipes, replace decayed wood, ventilate attics and crawl spaces, and eliminate wood-to-soil contact.[1][2][4][5]
Keep them out
Trim branches and shrubs away from the house, seal openings where utility lines enter, keep mulch to 2 to 3 inches, and store firewood off the ground and away from the building. Minnesota also says to prune branches that touch power lines, since the ants can travel along the lines into buildings.[1][2][4][5]
Traps and physical control
Find the nest by following workers after dark; a dab of sugar-and-milk or chopped mealworms draws them out so you can trail them back. Minnesota suggests a flashlight covered with red film, which the ants can't see, and Clemson suggests honey as bait to follow.[1][2][4][5]
Timing is a clue. Minnesota says carpenter ants seen indoors in winter, or in late winter and early spring, are coming from a nest inside the building, and large numbers of winged ants indoors are a sure sign of an indoor nest. One or a few winged or wingless queens are not; they are new queens looking for a place to nest.[4]
Pesticides
Once a nest is found, insecticide can be applied directly into it; dusts such as diatomaceous earth or borates blown into voids work as long as they stay dry. Both the parent and satellite nests must be eliminated or ants return. Sources differ on drilling: UC and Clemson describe drilling small holes to reach galleries, while Minnesota says drilling the roughly 1/8-inch holes is a job for a professional, not a homeowner.[1][2][4][5]
Spraying the workers you see doesn't work: it may cut the number of ants in sight for a while, but foragers carry little insecticide home and only a small share of the colony is out foraging at any time.[4][1]
If using bait, choose a slow-acting product labeled for ants; carpenter ants are finicky, so offer several and let them choose. Clemson says baits work well in some cases and poorly in others, possibly because the ants' food preference changes with the season, and that baits should go along the trails the ants follow.[1][5][2]
When to call a professional
Satellite colonies inside walls are hard to eliminate without professional tools; non-repellent perimeter treatments are available only to licensed applicators.[1][2][4][5]
Common questions
- Do carpenter ants eat wood?
- No. They excavate it for nesting and dump the shavings outside the nest; they feed on insects, honeydew and sweets.[1][2][4][5]
- I see big black ants inside. Is the nest in my house?
- Not necessarily. Workers often forage in from an outdoor nest; many winged ants at windows indoors point to an indoor nest. Minnesota says a few winged queens indoors don't mean there is a nest, but large numbers of winged ants do.[2][4]
- Will carpenter ants infest dry wood?
- They seldom tunnel into dry, sound wood; they prefer moist or decaying wood, so fixing leaks is key. Minnesota notes that satellite nests can be in drier spots, such as insulation, hollow doors and wall voids.[2][1][4]
- What does it mean if I see carpenter ants in winter?
- It means there is a nest inside the building. Minnesota says workers carried in on firewood can't start a nest, but ants active indoors in winter come from an indoor nest warmed by the house or by sunlight.[4]
Sources
- University of California Statewide IPM Program, “Pest Notes: Carpenter Ants, Publication 7416 (August 2009).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pncarpenterants.pdf (accessed 2026-11-11)
- Penn State Extension, “Carpenter Ants.” extension.psu.edu/carpenter-ants (accessed 2026-11-11)
- iNaturalist, “Camponotus taxon page (order and family).” www.inaturalist.org/taxa/62781 (accessed 2026-11-11)
- University of Minnesota Extension, “Carpenter ants.” extension.umn.edu/insects-infest-homes/carpenter-ants (accessed 2026-11-11)
- Clemson Cooperative Extension Home and Garden Information Center, “Carpenter Ants (HGIC 2406).” hgic.clemson.edu/factsheet/carpenter-ants/ (accessed 2026-11-11)
- Science Advances, via PubMed, “Koch et al. (2026), Beyond formic acid: peptides in carpenter ant venoms aid in disease protection, Sci Adv 12(20):eaed4078.” pubmed.ncbi.nlm.nih.gov/42127198/ (accessed 2026-11-11)