Start by identifying the ant problem you actually have
A few foraging ants at food are different from repeated large ants around damp wood. Health Canada lists several ants that can enter Canadian homes, but carpenter ants deserve a separate inspection because they excavate wood for nesting. They do not eat wood like termites. Indoors, carpenter-ant activity can be associated with moist or decaying wood, wall voids, window and door framing, insulation or other protected spaces.
Before choosing a treatment, note the ant size, where the trail begins and ends, whether activity is concentrated near a sink, window, roof leak or other moisture source, and whether there are sawdust-like shavings or winged ants. That evidence is more useful than treating every ant sighting as the same infestation.
Follow the route before you treat the workers
Health Canada recommends removing access to food and water and sealing cracks or openings that ants use. In a kitchen, clean crumbs and spills, seal attractive foods, rinse recycling and check pet-food areas. At the building exterior, inspect foundation cracks, utility penetrations, vegetation touching the structure and attached wood such as porches or sheds.
For carpenter ants, correct humidity or water problems and replace decayed material where appropriate. A surface spray that kills visible workers does not answer where the colony is. A recurring trail from one wall, window or damp cavity should shift the job from “kill the ants I see” to “find the route and nest conditions.”
Apartment and condo problems may cross unit boundaries
In multi-unit housing, photograph the trail and report where it enters or disappears. Plumbing penetrations, wall voids, garbage areas and shared exterior openings can make a one-unit treatment incomplete. Responsibility for repair and treatment depends on the province, lease facts and cause, so use the relevant local guide for the legal and municipal route rather than assuming the tenant or landlord always pays.
If you use a pesticide, match the label to both pest and site
Health Canada says to use only products registered in Canada and to confirm the pest and treatment location on the label. Look for the Pest Control Product (PCP) registration number. A product registered for an outdoor ant nest is not automatically an indoor wall-void treatment, and a product labelled for one pest should not be improvised for another.
When professional help makes sense
Use professional identification when you cannot distinguish the pest, when carpenter ants appear to be nesting in structural or concealed wood, when moisture damage needs investigation, or when repeated control does not stop activity. Health Canada specifically notes that established carpenter-ant colonies may require locating and treating the actual nest, and difficult situations may justify a professional exterminator.