The single most useful thing we tell people about ants is that they probably do not need us.
A line of small ants along a baseboard in Barrie in May is, in the overwhelming majority of cases, pavement ants foraging from a nest under the driveway. They are a nuisance. They are not eating your house, and a service call is not the proportionate response.
The ant that is worth money is a different insect entirely, and telling them apart takes about ten seconds.
The identification, in one look
Size settles it. Pavement ants are around 3mm — small enough that most people describe them as “tiny black ants”. Carpenter ants are 6 to 13mm and read as unmistakably large. If you are unsure whether an ant is big, it is not a carpenter ant.
| Pavement ant | Carpenter ant | |
|---|---|---|
| Size | ~3mm | 6–13mm |
| Where the nest is | Outdoors, under slabs and stone | Inside damp wood, often in the structure |
| Evidence left behind | A trail, and sand piled on pavers | Coarse frass shavings, often with insect parts |
| Damages the building | No | Slowly, in wood already wet |
| Usual answer | Bait, clean, seal the entry | Find the nest, and find the moisture |
Two other species turn up here often enough to name. Field ants build the mounds in lawns and along driveway edges and rarely come indoors at all — they are a lawn observation, not a pest problem. Odorous house ants are small like pavement ants but give off a distinct sharp smell when crushed; they are treated the same way.
Winged ants indoors in spring are a swarm from a mature nest, and they change the answer. That means an established colony, and if the ants are large it means an established colony inside the building. Our carpenter ant service covers what happens next.
Why pavement ants are everywhere in this city
The habitat is the driveway, and Barrie has built an enormous amount of exactly the right habitat.
Pavement ants nest in the sand bed under anything flat and hard: interlock driveways and walkways, patio stones, garage slabs, front steps, sidewalk sections, slab-on-grade porches. Sand-set pavers are effectively purpose-built nesting sites, and the newer subdivisions across the south and west of the city — Innis-Shore, Holly, Ardagh Bluffs — are full of them.
Then the climate works on it. Freeze-and-thaw cycling through a Simcoe County winter heaves the pavers, opens the joints, and washes the polymeric sand out of them. By the time the ground has thawed properly in spring, every joint is a doorway. The mounds of fine sand that appear between paving stones in May are the colony excavating its way back into shape.
Indoors, the routes are as predictable as the nests:
- Brick veneer weep holes, the deliberate gaps at the bottom course of the brick. They have to stay open — they drain the wall cavity — so screening rather than sealing is the fix.
- The expansion joint between a garage slab and the foundation wall.
- Under the door threshold, especially where a settled walkway has left the sill low.
- Utility penetrations where the water line, gas line or air conditioning line set passes through the wall.
- Basement window frames, particularly on the older housing in Allandale and the village cores out through Springwater and Innisfil, where the frame corners have rotted open.
What to do yourself, in order
Find the trail and follow it backwards. Ants navigate on a chemical trail, and it leads to the entry point. Twenty minutes of watching tells you more than any product.
Do not spray the trail. This is the mistake that turns a two-week problem into a season. Killing foragers removes the visible symptom and leaves the colony untouched, and with some species a repellent product causes the colony to split and relocate — one nest becomes several. The trail is the delivery route you actually want.
Bait, and be patient. A slow-acting bait is carried back and shared, which is how the colony rather than the foragers gets dealt with. Expect it to look worse for two or three days as recruitment increases, then decline over one to two weeks. Pulling the bait on day four because there are more ants than before is the most common reason it fails.
Take away the reason they are coming in. Ants forage for grease, sugar and water. Crumbs under the toe-kick, a leaking trap under the sink, a pet bowl left down overnight, a recycling bin with unrinsed tins. This is unglamorous and it does most of the work.
Then close the door. Once the traffic has stopped, seal the entry point you found — silicone at the threshold, mortar or foam at a utility penetration, stainless mesh across a weep hole rather than a plug.
Outside, deal with the joints. Sweep polymeric sand into the paver joints, keep mulch and soil back from the wall, and move the woodpile off the ground and away from the building.
When to call somebody
Six situations where the answer changes.
- The ants are large, or there is frass. Carpenter ants nest in wood that is already damp, so the finding is usually two problems — a colony and the water that made the wood attractive. Treatment without locating the moisture source is temporary.
- Winged ants indoors in spring. A mature colony, swarming from inside.
- You can hear them. A faint rustling in a wall void on a quiet night is a substantial nest.
- Bait has failed twice, properly. Correct product, left in place, two weeks each time. That usually means the nest is somewhere the bait is not reaching.
- A food business. Different standard entirely, and a documented programme by a licensed Structural Exterminator is part of operating.
- Recurring every single year in the same room. A colony with a route it likes, rather than an incidental foraging line.
What it costs, honestly
Carpenter ants — nest location, treatment and follow-up — run $350–$650 for a typical detached home, and more where there are multiple satellite nests. Those numbers and the rest of the trade’s pricing are set out in our pest control cost guide.
Pavement ants are a smaller job. An exterior perimeter treatment along the building line is $120–$200 as an addition to a visit. Booked on its own it is priced as a service call, and if you describe small ants on a spring trail on the phone we will usually tell you to try a bait first and call back if it does not work. That conversation costs us a booking and saves you one, which we think is the correct trade.
One note on the lawn
Ontario’s Pesticides Act restricts cosmetic pesticide use on lawns and gardens. Treating an ant mound in the middle of a lawn because it looks untidy is a cosmetic use. Treating the perimeter of a building against ants that are getting inside it is not.
It is why a licensed applicator will treat the building line and decline to blanket your grass, and why any product promising to clear every ant from your property is describing something that is not on offer here. The realistic goal outdoors is keeping the colony out of the house, not off the lot — the ants in the lawn were there before the house was, and after the first hard frost you will not see them again until spring.