Identification
Tetramorium immigrans — formerly lumped under Tetramorium caespitum in older BC literature — is the small dark brown ant most Metro Vancouver homeowners see spilling out of sidewalk cracks in summer. Workers are 2.5 to 4mm long, uniformly dark brown to nearly black, with paler legs. Under a hand lens you can see parallel grooves on the head and thorax and two small spines on the back of the thorax. The waist has two nodes, which distinguishes them from carpenter ants (one node) and odorous house ants (one node, hidden). Winged reproductives are much larger than the workers — up to 8mm — and show up in nuptial flights during the first warm humid evenings of late spring.
Habitat in BC
Pavement ants live where their name says they do: under paved surfaces. In Metro Vancouver that means nests under driveways, sidewalks, patios, foundation slabs, garage floor cracks, and the narrow seams between concrete and siding. They are thermophilic — they use the stored heat of concrete to shorten their brood cycles — which is why south-facing driveways and sunny patios are prime nesting sites. Indoor intrusions usually come up through baseboard cracks near a slab-on-grade section, sliding-door tracks, or the base plate along a garage-house wall. They are extremely common in 1960s–1990s Burnaby, Richmond, and Surrey homes with slab garages and concrete-patio rear yards.
Signs you have pavement ant
- Small piles of fine soil or sand pushed up between paving slabs or along driveway edges — these are the excavated nest material.
- Steady indoor trails 2–4mm wide along kitchen baseboards, under the dishwasher, or at the base of a sliding door.
- Workers swarming a dropped crumb, spilled pet food, or grease stain on the kitchen floor within an hour.
- Winged swarmers emerging from a foundation crack or driveway seam on a warm humid evening in May or June.
- Aggressive ant-vs-ant battles on the driveway in spring — pavement ants fight neighbouring colonies at territory boundaries.
Risk & damage
Pavement ants are almost entirely a nuisance pest. They do not damage structures, they do not bite or sting in any meaningful way, and they are not a documented disease vector for humans in the Pacific Northwest. The risk is strictly contamination of food surfaces — a kitchen counter with 200 ants on a sugar spill is not a health emergency, but it is a sanitation failure. For restaurants, cafes, and any food-service setting governed by Fraser Health or Vancouver Coastal Health, a visible Tetramorium immigrans trail during inspection can trigger a corrective-action order. Residentially, the risk is more about quality of life and the persistence of the problem than about any direct harm.
Seasonality in Metro Vancouver
Pavement ants are visible in Metro Vancouver from late March to mid-October with a clear mid-summer peak. Outdoor activity picks up when soil temperatures reach 10°C — typically early April in Vancouver proper, a week later in the Fraser Valley. Nuptial flights occur in late May and June on the first warm humid evenings after rainfall. Indoor foraging peaks in July and August when outdoor food is scarce and interior cooking residues are strongly attractive. Colonies remain active but hidden under paving through winter, with occasional warm-spell indoor trails in kitchens over slab-on-grade sections during January thaws.
Treatment approach
Treatment under Health Canada's Pest Control Products Act IPM framework starts with identification and trail-tracing to confirm Tetramorium immigrans versus carpenter or odorous house ants. We then apply a sugar-based or protein-based gel bait (matched to the season — pavement ants shift preference from protein in spring to sugars in summer), placed discreetly along known trails so workers carry it back to the queen. Non-repellent liquid baits are used along major trails. An exterior perimeter barrier treatment around the foundation slab and driveway edge prevents re-entry. Most pavement-ant jobs resolve in 7 to 14 days. The service is covered under our $139 quarterly plan, which is the more cost-effective option for homes with recurring driveway pressure.
When to call a professional
DIY bait stations from a hardware store can work for a single indoor trail if you match the bait type to what the ants actually want (protein in spring, sugar in summer) and resist the urge to spray. Call a professional if you've had trails for more than two weeks, if the trail persists after baiting, if you find ants in multiple rooms, or if you're seeing winged swarmers indoors — the last sign means a mature colony is established beneath your slab.
Prevention playbook
How to prevent pavement ant in Metro Vancouver homes
- 1
Seal foundation cracks and utility penetrations
Pavement ants enter through gaps as narrow as 1mm. Walk the perimeter and seal cracks in concrete slabs, around utility penetrations, and along siding-to-foundation transitions with exterior silicone caulk.
- 2
Disrupt trails on patios and driveways
Pour boiling water slowly over active ant trails on hard outdoor surfaces. The hot water breaks the pheromone trail signature and makes re-establishment take days rather than hours.
- 3
Store pet food in sealed bins
Dog, cat, and bird food sustains pavement-ant colonies faster than anything else. Keep kibble in metal or thick plastic containers and lift outdoor bowls after each feeding.
- 4
Keep mulch 30cm from the foundation
Organic mulch against the foundation retains moisture and harbours colonies. Replace the first 30cm against the building with gravel or river rock.
- 5
Bait with sugar-borax along foraging trails
Never spray indoor ant trails — it scatters the colony into satellite sub-colonies. Use a commercial sugar-based gel bait containing borax or spinosad; workers carry it back to the queen.
The Wild Pest service
See our Pavement Ant treatment page
Transparent pricing, 60-day return guarantee, same-day response across Metro Vancouver. Every treatment is documented with photos and service notes.
Frequently asked questions about pavement ant
Are pavement ants the same as sugar ants?+
'Sugar ant' is a catch-all term British Columbians use for any small house-invading ant. In Metro Vancouver, the two species most often called sugar ants are the pavement ant (Tetramorium immigrans) and the odorous house ant (Tapinoma sessile). They look similar at 2–4mm but Tapinoma crushed between your fingers smells like rotten coconut — a definitive field test.
Why are they suddenly everywhere on my driveway?+
What looks like a sudden bloom is usually a nuptial flight — reproductive ants emerging from established sub-driveway colonies on the first warm humid evening of May or June. They mate, the females lose their wings, and within 48 hours the visible swarm is gone. The colony has been there for years; you just didn't see it.
Can I just pour boiling water on the nest?+
It kills surface workers but rarely reaches the queen — pavement-ant colonies extend 30 to 60cm below the slab, and boiling water cools too fast. You'll knock down the visible trail for a week, then see it return. Targeted non-repellent bait is faster and more permanent. Do not pour bleach, gasoline, or commercial drain cleaner into a nest — these are illegal under BC environmental regulations and can contaminate groundwater.
My Burnaby townhouse complex has them on every unit's driveway — is that normal?+
Yes. Large paved areas with shared foundations — typical of Burnaby, Coquitlam, and Surrey townhouse complexes — support very large pavement-ant super-colonies that span multiple units. Unit-by-unit treatment rarely works long-term; complex-wide exterior perimeter treatment through a strata-level contract is the right scale. We do several of these each spring.
How do they get inside when the doors are closed?+
Under doors, through sliding-door tracks, up through hairline foundation cracks, around utility penetrations in garage walls, and along gas-line and water-line entry points. Pavement ants can squeeze through any gap wider than about 0.5mm. Sealing visible foundation cracks and weatherstripping under exterior doors reduces intrusion dramatically.
Related species