What We Found in a Glastonbury Crawlspace (and What It Teaches About Carpenter Ants)

The call was routine: a few big black ants on the kitchen counter every morning, a colonial built in the 1940s, homeowner had been spraying them with a hardware-store can for three weeks and "they keep coming back." Three weeks of repellent spray is usually where our real work starts — so this one's worth telling as a story, because everything about carpenter ants is in it.

The counter is never the story

Big black ants in a New England kitchen in May are carpenter ants until proven otherwise, and carpenter ants on a counter are commuters. The question is never "how do I kill these" — it's "where are they commuting from." So instead of treating the kitchen, we followed it backward: the trail ran behind the dishwasher, down through the cabinet kick plate, and into the floor framing. Which meant the crawlspace.

What the crawlspace showed

Flashlight, coveralls, and about thirty seconds of looking: a rim joist above the crawlspace's north corner with a scatter of coarse, sawdust-like debris below it — frass, the excavated wood carpenter ants push out of their galleries. Tap the sill above and it sounded papery. A moisture meter read the wood at over 20% — soaked, structurally speaking — because a downspout outside dumped roof water straight against that corner, and a dryer vent underneath kept the crawlspace air warm and damp.

That's the whole carpenter ant formula in one corner: moisture softens the wood, warmth keeps the colony working, and a satellite nest moves in. The main colony was almost certainly outside — likely the rotting oak stump we'd passed near the property line — with this sill nest as a satellite, and the kitchen as its food run.

Why the spray can made it worse

Three weeks of repellent spray on the counter had done two things: killed a few dozen expendable foragers, and taught the colony that the kitchen route was dangerous. Colonies respond to that pressure by budding — splitting into additional satellite nests. It's the most common way a one-nest problem becomes a three-nest problem, and it's why the can of spray is the most expensive cheap thing a homeowner can buy.

What actually fixed it

The treatment was almost anticlimactic, which is the point. A non-repellent application along the foundation and the trail routes — undetectable, carried home, shared through the colony including the satellite in the sill. Direct treatment into the gallery through the frass opening. And the part no product can do: we showed the homeowner the downspout, they added an extension to carry water away from the corner, and the dryer vent got rerouted. Activity dropped inside a week; a follow-up check found the galleries quiet.

The takeaway for your house

If you're seeing large black ants indoors — especially in spring, especially in a house older than 1970 — the checklist writes itself: don't spray, watch where they go, and think about where your house is wet. Gutters, downspout corners, deck ledgers, anywhere plumbing sweats. Carpenter ants are less a pest problem than a moisture problem with legs, and treating the ants without fixing the water just schedules the sequel.