Why do you have ants in the house and what to do ?

Why do ants come in suddenly ?

An ant wandering alone on your counter is never alone. It's a scout. Its mission: to find something to feed its colony. If it succeeds, it leaves behind a pheromone trail that guides the other workers to the source.

In Quebec, ants come into homes for three main reasons:

• Food — crumbs, juice stains, spilled sugar, a pet bowl left outside
• Water — a leak under the sink, condensation around pipes, a damp basement
• Shelter — especially carpenter ants that tunnel into damp or decaying wood

The 5 common ant species in Quebec

Each species has specific behaviour and treatment. Correctly identifying yours is the first step — that's what separates an effective treatment from an intervention that makes the situation worse.

1. The carpenter ant

Size: 6 to 12 mm — the largest of our common species. Colour: black (sometimes reddish).

It does not eat the wood, but it tunnels galleries into it to nest. Targets: damp wood, framing, worn window frames, decks. The damage can be significant if the colony has been established for a long time.

Signs: fine sawdust (frass) under woodwork, crackling sounds in the walls at night, winged workers in spring.

2. The Pharaoh ant

Size: 2 mm — tiny. Colour: yellow to reddish-brown, almost translucent.

The hardest species to eliminate. It loves multi-unit buildings, hospitals and low-income housing. Notable trait: if you spray it with a consumer insecticide, the colony reacts by splitting up (budding) — one colony becomes several.

Signs: very fine trails near water sources (bathroom, kitchen), 24/7 activity, present all year round (it lives inside the walls).

3. The odorous house ant

Size: 3 mm. Colour: brownish-black.

Its name comes from the smell it gives off when crushed: a note of rancid coconut or blue (mouldy) cheese. It comes in mainly looking for sugar.

Signs: marked trails toward the kitchen or the garbage, increased presence after rain.

4. The thief ant

Size: 1.5 mm — even smaller than the Pharaoh ant. Colour: pale yellow.

Its name describes its behaviour: it lives as a parasite of other ants' nests and steals their food. Often mistaken for the Pharaoh ant, which leads to bad diagnoses.

5. The black field ant

Size: 4 to 5 mm. Colour: black.

The most common outdoors: nests under pavers, decks, lawns. It comes in during the summer when it's hot and dry to look for water and food.

How to identify where they come from

Finding the nest is more effective than killing the workers. Here's the method to trace the trail back:

1. Follow the trail — watch for a few minutes without intervening, spot where they come from and where they go
2. Look for the entry point — a window crack, a baseboard joint, a pipe passage, a crack in the foundation
3. Spot the damp areas — under the sink, around pipes, in the basement
4. Inspect the wood — window frames, decks, basements. Tap gently: if it sounds hollow, carpenter ants are likely
5. Check the exterior — often the main nest is outside, in a tree or under pavers, and only the workers come in

8 methods to eliminate them and prevent their return

1. Identify the species first

Treatment varies radically between a carpenter ant and a Pharaoh ant. If you're unsure, take a close-up photo and send it on WhatsApp — a technician identifies it within a few minutes.

2. Clean the trails immediately

Use a 50% water / 50% white vinegar mix on visible trails. It erases the pheromones and disorients the scouts. A temporary but useful method.

3. Store food in airtight containers

Sugar, flour, cereal, pet kibble — anything that can attract them must be sealed up. Empty the garbage regularly, especially in summer.

4. Fix water leaks

Leaks under the sink, around the toilet, cracks in the drains. Moisture is a magnet — especially for carpenter ants that need damp wood to nest.

5. Seal cracks and entry points

Caulk all openings larger than 1 mm around window frames, baseboards and pipe passages. Ants always find a way if you leave them one.

6. Keep vegetation away from the wall

Tree branches and shrubs touching the house are highways for carpenter ants. Keep at least 30 cm of clearance between vegetation and the façade.

7. For Pharaoh ants: gel baits only

If you suspect a Pharaoh ant, forget the insecticide. Buy a gel bait (such as Maxforce, Advion) at the hardware store or call a professional. Apply with a brush along the trails, at several strategic points.

8. Call a certified exterminator if the infestation persists

After 2 weeks of corrective measures, if the presence does not decrease, it means a nest is established in your home. A professional treatment (species identification, nest location, exterior perimeter barrier + targeted interior baits) remains the only lasting solution.

Frequently asked questions