Spotting large black ants in or around your home isn’t just annoying—it’s a serious warning sign. These aren’t merely kitchen pests. They’re Carpenter Ants, native insects common to Toronto and Eastern Canada, capable of quietly causing substantial structural damage. If you’re seeing even a few indoors or around your home, there’s a high chance significant hidden damage is already underway.
The Hidden Structural Threat
Carpenter Ants don’t consume wood; they excavate it, creating elaborate nesting galleries. Unlike termites, Carpenter Ants do not ingest the wood—they discard it as fine sawdust-like frass. This behavior makes them especially resistant to pressure-treated wood, which is impregnated with insecticides that can kill termites upon ingestion. For Carpenter Ants, the wood is simply a structural material—not a food source—and this distinction has serious implications for treatment.
At Pest UnHABITAT, our “post-mortem” inspections frequently reveal hollowed beams, rafters, and joists(horizontal wooden supports that hold up floors and ceilings), where nails and screws anchor into nothing but thin air. These ants embody the true meaning of a structural pest—not merely pests found in structures, but ones that significantly impact structural safety.
Selective Nesting Habits
Carpenter Ants prefer thicker, substantial horizontal wood, especially at structural joints or moisture-prone areas. They typically avoid thin pieces of wood but can infest both shaded and sun-exposed surfaces. Importantly, Carpenter Ants are not selective based on the age of the wood—they infest both new and old wood alike. Their nests commonly occur in:
Joists (floor joists, ceiling joists) and decking
Rafters and fascia boards (sloped roof supports and the vertical trim along roof edges)
Structural beams exposed intermittently to moisture
Serious, Hidden Damage
The visible nuisance of Carpenter Ants masks a much greater problem. Their nests often result in compromised structural integrity, affecting everything from roof stability to floor safety:
Damaged fascia and roofing can lead to wildlife entry (raccoons, squirrels) and costly water damage, flooding basements.
Structural weakening may result in sagging floors and broken tiles caused by a flexing floor due to an incapacitated joist.
Critical support elements like deck ledger joists or rafters might require costly removal and replacement.
Extracting a single joist from a finished ceiling, or a rafter from beneath layers of shingles, underlayment, and sheathing, is far from a simple surgical operation. It can mean dismantling substantial parts of your home—work that demands time, skilled labor, and significant expense.
Moreover, Carpenter Ants rarely limit their activity to a single location. They typically establish a network of nests, simultaneously attacking various parts of your home, including rafters, fascia boards, deck joists, and even detached structures like sheds.
Simply removing affected wood without professional extermination can worsen the situation. Disturbing nests can push ants to relocate and continue damage elsewhere, prolonging the infestation cycle.
Challenging to Treat
Their protected nesting sites inside wood offer Carpenter Ants shelter from the weather and many common insecticides, including wood treated with chemical preservatives. Eradicating them requires targeted, professional treatments.
Even successful treatments can take weeks to eliminate the main nest, followed by managing secondary nests—sometimes taking years. If the colony’s queen resides off-site, recurring infestations are likely, with new generations emerging annually.
Early Signs of Carpenter Ant Infestation
While sawdust-like piles and hollow-sounding wood are indicators, these signs aren’t always visible if nests are hidden within walls or insulated spaces. Key signs to watch for include:
Intermittent sightings of Carpenter Ants (even just a few ants can indicate a hidden infestation; the visible ones are merely a side-show to deeper hidden activity)
Winged ants emerging in spring
Sawdust-like frass, sometimes mixed with insect parts, near structural wood, walls, or within cobwebs
Carpenter Ants trapped or visible within cobwebs
Sawdust-like insulation foam debris around walls or wood joints
Why Store-Bought Treatments Fall Short
Carpenter Ant infestations require professional expertise and targeted treatments. Store-bought solutions are rarely effective against these well-protected ants. While DIY products might suffice for certain ant species, Carpenter Ants demand a specialized approach.
Effective Preventive Measures
Taking proactive measures can significantly reduce Carpenter Ant risks:
Maintain your roof and replace any compromised or hollowed wood.
Ensure gutters and downspouts are clean and properly direct water away from the house.
Regularly check drainage around your home during rains.
Keep your home, yard, and structures dry. Painting or sealing outdoor wood helps keep moisture out, indirectly reducing attractiveness.
Install flashing at ledger joists of decks or patios. (flashing is a protective barrier that redirects water away from joints)
Regularly clear debris accumulation near structural wood and exterior walls, as it can trap moisture and attract insects (Carpenter Ants are insectivores).
Promptly address all leaks—whether from plumbing, roofing, or elsewhere.
Engage your neighbors in prevention and collective treatment efforts. Carpenter Ant territories often span multiple properties, making cooperative action the most effective strategy. Consider sharing this blog post with your neighbors to inform and encourage coordinated efforts.
Identifying Carpenter Ants
Carpenter Ants are polymorphic, meaning they vary in size and appearance depending on their caste. Within a single colony, you may see:
Minor workers: smaller ants handling brood care and foraging
Media workers: mid-sized, versatile in tasks
Major workers (soldiers): larger, with strong mandibles used for defense, excavation of wood, processing tougher food, and carrying larger items
All worker ants are female. In addition to workers, Carpenter Ant colonies produce winged males and future queens during the spring and summer. Males typically die shortly after mating. Fertilized queens shed their wings following their nuptial flight and seek out wood to establish new colonies—making early detection and intervention essential.
Protect Your Home
Carpenter Ants quietly jeopardize the structural integrity and safety of your home. Spotting these large black ants signals the need for professional intervention.
Not sure if you have Carpenter Ants? Contact Pest UnHABITAT for a professional inspection.
Other ants can also be problematic—we occasionally encounter non-native species with unusual behaviors and nesting structures that make ant control a specialized branch of pest management. The ant world is animated by quite the cast of characters:
Ghost ants – tiny, pale, and almost invisible
Thief ants – masters of sneaking food from other colonies
Pharaoh ants – infamous for feeding on blood and other bodily fluids
Odorous house ants – stink when crushed
Fire ants – sting first, ask questions later
Citronella ants – emit a pleasant lemony scent when crushed
Pavement ants – the “lesser evil” that pushes out stinkier rivals; let the pavement ants live! (outside!)
Acrobat ants – genuinely acrobatic; we’ve seen them carry items heavier than themselves upside down on smooth plastic surfaces, seemingly defying gravity
Aphid-farming ants – raise aphids like cattle, harvesting sweet honeydew by milking it out of an aphid’s anus
Crazy ants – the definition of antsy: they zigzag nervously and change direction like they’re dodging invisible obstacles
Big-headed ants – most are petite, orderly trail-followers—until one comes along with a comically oversized head
Carpenter Ants – surprisingly good swimmers, as if their wood-chewing talents weren’t enough
Mystery ant – a foul-tasting ant that likes to get into people’s food and ruin its flavor (we’ll leave it up to you to guess which one from the list it is!)
Have a guess? Fill out our contact form and let us know! And for any ant issues—from structural invaders to exotic nuisances—trust Pest UnHABITAT for expert diagnosis and effective, focused solutions.