Carpenter Ants in the West Island — Pierrefonds-Roxboro & Dollard-des-Ormeaux

Published May 15, 2026 · Extermination DMP

The West Island has the worst carpenter ant pressure on the island of Montreal. Pierrefonds-Roxboro and Dollard-des-Ormeaux in particular are built on a combination that carpenter ants treat as a buffet: 1960s-1980s bungalow stock, mature trees, and properties that back onto the Rivière des Prairies marshlands.

Why the West Island scores 90+ year after year

• Bungalow construction era. Suburban bungalows built 1960-1985 used dimensional lumber framing and basement walk-out sliders that are now well past their original moisture-barrier life.
• Mature trees within 5 metres of the house. Every West Island street has decorative maples and pines planted with the original subdivision — those trees are now 40-60 years old, hollow at the core, and producing satellite colonies in every direction.
• Cap-Saint-Jacques and Bois-de-Liesse green corridors. Provide a permanent reservoir of parent colonies that re-seed the residential blocks every summer.
• Sprinkler systems. West Island homeowners over-water foundation plantings, keeping the wood near the house chronically damp — a carpenter ant magnet.

Where they enter the typical West Island bungalow

1. The bay window sill (south or west side, due to sun + moisture cycle)
2. The original wood deck ledger board bolted to the house
3. The basement walk-out slider door frame
4. The garage-to-house door frame (especially if the garage has a leak)
5. Bathroom and kitchen subfloors where original copper plumbing has slow leaks

The annual cycle

• April-May: Workers emerge from overwintering. Sightings on warm days. This is the optimal treatment window.
• June-July: Swarmers (winged reproductives) appear. If you see flying ants inside the house, you have a mature colony.
• August: Peak activity. Trails inside walls, frass piles visible.
• September-October: Activity slows but does not stop. Treatment still effective.
• November-March: Colony dormant inside the structure. Cannot be eliminated until spring re-activation.

What works in the West Island

1. Tree base treatment. Identify the parent colony tree(s) within 50m. Treat the trunk with a non-repellent that workers carry back to the queen.
2. Perimeter foundation treatment. Non-repellent application along the entire foundation creates a transfer zone.
3. Interior bait at active trails. Slow-acting protein/sugar bait kills satellite colonies inside walls.
4. Moisture remediation. Fix gutter leaks, regrade soil away from foundation, replace any rotted sill plate or deck ledger. Without this, retreatment is needed annually.

Cost and timeline

Single-family bungalow with one parent tree: $475-$750 for initial treatment + 2 follow-ups. Properties with multiple parent trees (West Island norm): $750-$1,150. Annual prevention contract: $385/year covering 2 perimeter treatments + 1 inspection. Strongly recommended for properties backing onto marshlands or wooded green corridors.

FAQ

Can DIY work in the West Island?

For a single visible trail with no structural damage and no winged ants, store-bought bait can suppress activity for 2-4 weeks. For anything more advanced — frass piles, swarmers, multiple trails — DIY consistently fails because the parent colony is outside the property line and cannot be reached with retail products.

Will my structure be damaged?

Carpenter ants do not eat wood for food. They excavate it for nesting. Structural damage takes years to develop and is usually limited to the immediate area of the nest. Damage is rare in homes treated within the first season of detection.