Carpenter ants are Ontario’s largest ant species (6–13mm), typically black or red-black. Crucially, they don’t eat wood — they nest in it, excavating smooth galleries in moist or decayed timber. The telltale sign: piles of fine sawdust-like material called frass near wood surfaces. If you find frass in your basement or attic, call a professional immediately.

Store all food in sealed containers — pet food, sugar, and honey are prime targets. Fix all plumbing leaks and maintain dry basements (Carpenter ants are attracted to moisture-damaged wood). Seal cracks in foundation walls, window frames, and where utilities enter. Remove firewood stored against the house exterior.

Ant bait stations (e.g., Terro, ~$8–12 at Home Depot) are far more effective than sprays. Worker ants carry the slow-acting poison back to the colony and queen — eliminating the source rather than just surface ants.

Diatomaceous Earth (food-grade) is a safe, non-toxic physical killer. Dust it along ant trails — the microscopic particles puncture the ants’ exoskeleton. Safe for pets and children once settled. Avoid inhaling the dust during application.

Call a licensed pest control company if: you find frass (sawdust piles), you see large ants in your basement or attic in numbers, or DIY treatment shows no improvement after 2 weeks.

Cost reference: $200–$500 for single treatment; $600–$900 for multi-visit programs. When buying a home, ask your inspector to check basement beams and attic framing for frass and moisture-damaged wood — this is a legitimate negotiation item.

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