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Pest Library · Crawling insectsCarpenter Ants Identification Guide
How to identify carpenter ants, the large black ants that damage wood in Ontario homes and cottages.
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How to identify
What carpenter ants look like
Carpenter ants are large black ants, the biggest ants you will see in Ontario homes. They have a single node between the thorax and abdomen and an evenly rounded back.
Winged swarmers appear in spring when a mature colony is ready to expand.
Signs you have carpenter ants
- Large black ants indoors, especially in spring
- Fine sawdust (frass) under windows, baseboards or beams
- Winged ants indoors in spring
- Faint rustling inside walls
- Damaged or hollow-sounding wood near moisture
Are they dangerous?
Carpenter ants do not eat wood, but they hollow it out to nest. Over time they can weaken window frames, decks, sill plates and roof structures, especially where wood stays damp.
How to prevent them
- Fix roof, gutter and window leaks
- Replace water-damaged wood
- Trim branches touching the roof or siding
- Store firewood away from the house
- Keep wood from touching soil
Quick facts
Scientific nameCamponotus pennsylvanicus
Size6–13 mm
ColourBlack, sometimes reddish
Most activeSpring and summer
Found inDamp wood, decks, windows, cottages
Risk levelModerate (wood damage)
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