Carpenter Ants in the Wall

Large black ants indoors in February in Maine are not visiting. Nothing is foraging in from outside in the snow, so ants moving around a warm house in late winter usually means a colony inside the structure.

Confirming it

• Coarse frass below a window, a door frame, a sill or a ceiling joint
• A faint rustling in a wall void when the house is quiet
• Winged ants at an interior window in spring
• Ants consistently appearing at the same spot rather than trailing from a door

Where the water usually is

1. Window and door seals that have failed
2. A gutter line overflowing onto a sill or a corner board
3. The framing behind a shower or a tub surround
4. A porch post or deck ledger in ground or standing-water contact
5. Roof deck under a past ice-dam leak
6. A crawlspace with no vapour barrier

Treatment

Treatment targets the colony where it lives — injected into the galleries when they are reachable, or carried back by foragers through bait when they are not — and then addresses the satellite-parent relationship: mature colonies keep a parent nest outside, often in a stump, a dead limb or a woodpile, and a satellite in your wall. Killing only the satellite leaves the source producing.

The report names the moisture condition and what would fix it. That part is not pest control, and it is the part that decides whether the ants come back.

Free residential inspection, honest answer. Call or text 207-740-4441.

The satellite and the parent

A mature carpenter ant colony rarely lives in one place. The parent nest — with the queen — is often outdoors in a stump, a dead limb, a woodpile or a section of fence, and the satellites are the ones in your wall, your window frame or your porch column. Satellites contain workers and brood, and they are what you see indoors.

That relationship is the reason the exterior inspection matters as much as the interior one. Treat only the satellite and the parent replaces it. Treat both and the pressure stops. The exterior walk covers the tree line, any wood in ground contact, stumps within reasonable foraging distance, and how branches connect to the roof.

What happens after treatment

Activity often increases for a few days as the colony is disturbed and foragers redistribute. That is expected. What matters is the trend across two to three weeks, and whether new frass appears after the galleries have been cleaned off. We tell households to wipe the frass away after treatment precisely so that new frass means something.

What you can check before we arrive

• Tap along the suspect wall or sill. Galleries sound hollow against solid framing.
• Look for frass at floor level below windows, doors and ceiling seams, and check again a day after sweeping it up.
• Look after dark. Carpenter ants are most active at night — UMaine puts the peak between 10 pm and 2 am — so a flashlight after dark, and a few minutes following one ant, usually points at the route.
• Check outside for wood touching soil, branches touching the roof, and gutters overflowing onto trim.
• Photograph what you find, with something for scale.

None of that is required, and all of it shortens the inspection.

What the treatment actually involves

Where galleries are reachable, treatment is applied directly into the void rather than sprayed across a surface. Where they are not, a non-repellent material or a bait the foragers will carry does the work. The exterior parent nest, if there is one, is located and treated in the same visit wherever possible, because leaving it produces a new satellite in a new wall.

Expect a few days of visible activity afterwards. That is disturbance, not failure. The measure is whether new frass appears over the following two to three weeks once the old frass has been cleaned up.

The repair conversation

Carpenter ants do not create the moisture, they find it. Where the framing is soft, treatment stops the colony and the wood stays soft, which means the next colony finds the same conditions. The report names the source — a failed window seal, a gutter line, a shower pan, a porch post in ground contact — with a photograph, and says plainly that the repair is carpentry rather than pest control.

Houses that fix the water rarely call us back about carpenter ants. Houses that do not, do.

More on ant control · Updated 2026-10-04