Harmless to people. A large worker can pinch with its jaws and may spray formic acid into the wound, which stings briefly. There is no sting and nothing medically significant.
Size6–13 mm, varying within one colony
MarkingsLarge for an ant, 6–13 mm, with big workers and small workers in the same nest · Uniformly matte black, with fine golden hairs on the abdomen
WhereDamp or decaying wood — window frames, sills, roof leaks, porch posts, and dead branches and stumps outdoors.
SeasonActive spring to autumn; winged swarmers appear in spring
How to tell it apart
Large for an ant, 6–13 mm, with big workers and small workers in the same nest
Uniformly matte black, with fine golden hairs on the abdomen
Evenly rounded thorax in profile — no spines or bumps
One node on the waist, and elbowed antennae
Coarse sawdust-like shavings below a nest opening, often with insect parts in it
Where you’ll find it
Across the eastern and central United States, with Camponotus species nationwide.
Damp or decaying wood — window frames, sills, roof leaks, porch posts, and dead branches and stumps outdoors.
Active spring to autumn; winged swarmers appear in spring.
How it behaves
They do not eat wood. They excavate galleries in it to nest, which is why the debris beneath an opening is clean shavings rather than the mud-packed residue a termite leaves. Crucially they strongly prefer wood that is already damp or decaying, so a carpenter ant problem indoors is usually a moisture problem first — a leaking gutter, a failed seal, a bathroom leak — and treating the ants without fixing the water simply repeats the process next year. They forage widely at night, mostly for other insects and sugars.
You’ve found one indoors
Find the water before you find the ants. Look for the source of damp wherever the shavings are appearing, and expect the nest to be near it. Outdoors, keep firewood off the ground and away from the house, and cut back branches touching the roof. A trail of large black ants indoors at night is worth following back rather than simply wiping away.
Common questions
Do carpenter ants eat wood?
No. They tunnel through it to nest and push the shavings out. The clean sawdust is the difference from termites, which consume the wood and leave mud behind.
Do they bite?
A big worker can pinch, and may add formic acid, which stings for a few minutes. It is not a sting and it does no harm.
How bad is the structural damage?
Slower and usually less severe than termites, but real over years — and it is concentrated exactly where the wood is already wet and weakened.
I found winged ants indoors in spring. Termites?
Look at the waist and antennae. Ants have a pinched waist and elbowed antennae; termites have a straight-sided body and straight antennae. Both swarm in spring and that is when the two get confused.
Emmett Collins-Sussman · CC-BY