Every spring, thousands of Ontario homeowners discover they have a carpenter ant problem — often long after the damage has started. Carpenter ants (Camponotus pennsylvanicus) are Ontario’s largest ant species, ranging from 6mm to 25mm in length, and they prefer damp, decaying wood found in walls, window frames, decks, and roof eaves.

The tricky part? Most infestations go unnoticed for months. Here are the 5 most reliable signs that carpenter ants have moved into your home.

Sign #1: You’re Seeing Large Black Ants Indoors

Carpenter ants are large — noticeably bigger than pavement ants or little black ants. They’re typically jet black, though some species have reddish-brown colouring on their thorax. If you’re spotting ants 12mm or longer crawling through your kitchen, bathroom, or basement — especially at night — you likely have an indoor nest nearby.

Occasional sightings (1–2 ants) in spring might be scouts from an outdoor colony foraging for food. But if you’re seeing them consistently, or in larger numbers, there’s a good chance a satellite colony has already formed inside your walls.

Sign #2: Sawdust-Like Frass Near Walls or Windowsills

One of the most definitive signs of carpenter ants is frass — a fine, sawdust-like material pushed out of their galleries. Unlike termite frass (which looks like tiny pellets), carpenter ant frass is a mix of wood shavings, soil particles, dead ant body parts, and insect debris.

Check near windowsills, door frames, baseboards, and anywhere wood meets moisture. Finding frass is a near-certain confirmation of an active nest within the structure.

Sign #3: Rustling or Crinkling Sounds in Your Walls

Carpenter ant colonies can grow to 10,000+ workers. When they’re active — especially at night — you can often hear a faint rustling, crinkling, or crackling sound coming from inside walls, ceilings, or floors. This is the sound of ants moving through tunnels and excavating wood.

Try pressing your ear against walls near areas where you’ve spotted ants, particularly in bathrooms, kitchens, or anywhere with past moisture problems. If you hear activity, the colony is well established.

Sign #4: Winged Ants (Swarmers) Appearing Indoors

In late spring and early summer, mature carpenter ant colonies produce winged reproductive ants (alates) that swarm to start new colonies. Finding winged ants inside your home — especially near windows or light sources — is a serious warning sign. It means the indoor colony is mature enough (typically 3–6 years old) to reproduce.

Important: Many homeowners mistake winged carpenter ants for termites. The key differences: carpenter ants have a pinched waist, elbowed antennae, and forewings longer than hind wings. Termites have a straight body, straight antennae, and wings of equal length.

Either way, winged insects emerging indoors means it’s time to call a professional immediately.

Sign #5: Soft, Hollow, or Damaged Wood

Tap on wood surfaces where you’ve noticed ant activity — window frames, deck boards, fascia boards, or structural beams. If the wood sounds hollow, feels soft, or crumbles, carpenter ants may have excavated galleries inside.

Unlike termites that consume wood fibres, carpenter ant galleries are smooth and clean — almost polished looking. If you find this type of damage, the infestation may have been active for years and structural repairs could be necessary alongside pest treatment.

Frequently Asked Questions