Carpenter Ant Control in York Region

Carpenter ants are the big black ants that show up inside York Region homes each spring, and this is the pest this region calls about most. Unlike the small kitchen ants, these nest inside your wood. They do not eat it. They chew galleries through damp or damaged framing to open room for the colony, and left alone they slowly weaken it. The mature treed estate lots and large detached homes across Thornhill, Unionville, Markham, Richmond Hill, and Aurora, many backing onto the Oak Ridges Moraine, are prime carpenter ant country: old trees, wood decks, and the moisture that goes with both. The first job is always telling them apart from termites, because the two get confused constantly and the response is different. Most carpenter ant jobs run $250 to $500, because the work is finding the nest, not spraying a trail. Big black ants indoors plus little heaps of what looks like sawdust is the classic sign, and it almost always means moisture somewhere in the structure.

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Carpenter ant or termite? How to tell them apart

Start here, because the treatments and the stakes diverge. Good news for York Region: termites turn up in pockets of the GTA but are far rarer than carpenter ants, so the large black insect on your kitchen floor is almost certainly an ant, especially on the older treed lots where carpenter ants thrive.

Here is how they differ if you can get a close look:

• Waist. Carpenter ants have a pinched, narrow waist between thorax and abdomen. Termites have a straight, thick body with no waist.
• Antennae. Ant antennae are bent, like an elbow. Termite antennae are straight and look like a string of tiny beads.
• Wings (on the flying ones). Both swarm, but a carpenter ant swarmer has two pairs of wings of different lengths, front pair longer. A termite's four wings are all the same length.
• What they do to wood. Carpenter ants excavate clean, smooth galleries and push the debris out. Termites eat the wood and pack their tunnels with mud. Carpenter ant galleries look sanded; termite damage looks dirty.

Carpenter ants do not eat wood. They excavate it to nest, and the tell is the sawdust they push out, called frass, piling up below the hidden gallery. A small cone of coarse sawdust with bits of insect in it is frass, and it points almost straight up at the nest above it.

Health Canada's Pest Management Regulatory Agency registers the products used for both, and both are worked by a licensed technician, but confirming which insect you have decides the whole plan. If it turns out to be small kitchen ants instead, the general ant control page covers those.

The signs it is carpenter ants

• Large black ants indoors, often a quarter to half an inch long, especially in spring and at night when they forage.
• Frass: small piles of coarse sawdust, sometimes mixed with insect parts and dead ants, under baseboards, in basements, below window frames or in the garage.
• A faint rustling or crackling inside a wall or ceiling void when the house is quiet, the sound of a large colony working the wood.
• Swarmers in May or June: winged carpenter ants gathering at a window are a strong sign of a mature nest inside the structure, not just foragers passing through.
• Ants concentrated around moisture: a leaky roof, a bad window seal, the wood around a bathtub, a damp basement sill. That is where they nest first.

Moisture is the root cause, always

Carpenter ants will not attack sound, dry wood by choice. They move into wood that has already gone soft: damp, previously water-damaged, or beginning to rot. On York Region's larger homes and estate lots that usually means one of a short list: a roof leak that has wet the attic sheathing, a window that has fed water into the framing, a chronically damp basement sill, a deck ledger or post that never fully dries out, or wood sitting in contact with soil at the edge of a wooded yard. The big decks, wooded backyards, and mature landscaping that make these Thornhill, Unionville, and Aurora properties desirable are also what feed the colonies. Find the moisture and you have usually found the nest, or at least the reason it is there.

How we actually clear carpenter ants

The difference between a lasting fix and a repeat call is whether the technician finds the nest. Spraying the trail kills foragers and does nothing to the colony in the wall.

1. Inspection (free). We follow the trails, look for frass, sound out the wood, and locate the moisture. Carpenter ants often keep a main nest outdoors, in a stump, woodpile, or fence post, and satellite nests inside the home. On a treed York lot the parent nest is frequently in a backyard tree or old stump, so we trace both.
2. Find and treat the nest. Once the nest or gallery is located, we treat it directly, and we bait or treat the trails the workers use between the outdoor parent nest and the indoor satellite, so the whole colony is hit, not just the part you saw.
3. Address the source. We tell you the moisture problem feeding them: the leak, the rot, the wood-to-soil contact. Fixing that is what keeps the next colony out.
4. Follow-up. We return to confirm activity has stopped and the frass is not building back up.

Do you need a pro, or can you do it yourself?

Carpenter ants are one of the pests where do-it-yourself rarely works, because the entire problem is the nest you cannot see. A store bait might thin the foragers, but it will not find the gallery in the wall or the parent nest out in the yard, and it does nothing about the moisture that invited them in. If you are seeing big black ants indoors on a regular basis, finding frass, or hearing anything moving in the walls, that is a call. Our honest do-I-need-an-exterminator guide covers where the line sits.

Common questions

Reviewed August 2026.

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