Overview
Carpenter ants (Camponotus pennsylvanicus) are the most destructive insect pest in Quebec that most homeowners consistently underestimate. They do not eat wood — they excavate it, carving smooth galleries through structural lumber to create nesting space. Over time, this excavation weakens beams, joists, and framing in ways that are expensive to repair and dangerous to ignore. A colony that has been active for 5+ years can cause tens of thousands of dollars in structural damage.
How to Identify Carpenter Ants
- Size: Workers 6–13 mm; queens up to 18–20 mm — the largest ants you will encounter in Quebec
- Colour: Primarily black, sometimes with reddish-brown colouring on the thorax
- Body shape: Single, rounded node (petiole) between thorax and abdomen — evenly rounded thorax profile when viewed from the side
- Antennae: Elbowed (bent at a distinct angle), constantly moving
- Wings: Reproductive forms have two pairs of wings; front wings noticeably larger than hind wings
- Movement: Fast, purposeful, and direct — follow established trails
- Frass: Coarse sawdust mixed with insect fragments expelled from galleries
Biology & Colony Structure
- Parent colony: Located outdoors in moist, decaying wood — contains the queen and is the reproductive centre
- Satellite colonies: Located indoors in moist structural wood — contain workers, older larvae, and pupae; no queen
- Colony size: 3,000–10,000 workers across all nests combined in a mature colony
- Colony age: A colony large enough to cause significant structural damage is typically 3–6 years old
- Foraging range: Workers forage up to 100 metres from the nest
- Activity: Primarily nocturnal; most active between 10 PM and 2 AM
- Preferred wood: Moist, softened wood with moisture content above 15%
Risks
- Structural damage: Galleries weaken load-bearing elements over time — a 5-year-old colony can cause $10,000–$50,000 in structural damage
- Electrical fire risk: Carpenter ants sometimes nest near electrical wiring and can damage insulation
- No direct health risk: Carpenter ants do not transmit diseases and rarely bite humans unless directly handled
- Mould association: The moisture conditions that attract carpenter ants also promote mould growth
Signs of Infestation
- Frass: Coarse sawdust mixed with insect fragments — found under windows, along baseboards, in basement corners
- Large black ants indoors: Especially at night or in spring (April–June)
- Winged swarmers indoors: Definitive evidence of a mature colony inside the structure — typically April through June
- Rustling sounds: Faint crinkling or rustling inside walls, especially at night
- Structural symptoms: Doors or windows that don't close properly, soft or springy floors, hollow-sounding wood
- Smooth, clean galleries: Visible in exposed wood — unlike termite galleries, which are rough and muddy
Prevention
- Fix all roof leaks, plumbing leaks, and gutter failures promptly — moisture-damaged wood is the primary attractant
- Trim tree branches to at least 2 metres from the roofline and 1 metre from exterior walls
- Remove dead trees, stumps, and decaying wood from the property
- Store firewood at least 6 metres from the house, elevated off the ground
- Seal gaps in the foundation, around utility penetrations, and at the sill plate
- Inspect and replace water-damaged wood around windows, doors, and decks
- Schedule annual spring inspections (April) for early detection
Professional Treatment
Professional carpenter ant treatment requires locating both the indoor satellite colony and the outdoor parent colony. Treatment includes: direct nest treatment (insecticide dust injected into galleries through small access holes), exterior perimeter spray (residual insecticide barrier around the complete exterior), interior crack and crevice treatment, and granular bait for the outdoor parent colony. Follow-up visit 4–6 weeks after initial treatment. All Blackline treatments include a 90-day guarantee.