Spotting a steady trail of large black ants going in and out of a tree is unsettling — and a fair question follows: are the ants killing the tree? Usually not. But they're often telling you something important about it.
Ants signal decay; they don't cause it
Carpenter ants don't eat wood and they don't bore into sound, healthy timber. They excavate their nests in wood that's already soft — decayed, moisture-damaged, hollowing. So a carpenter ant colony in a tree is less a cause than a symptom: it usually means there's existing internal decay providing them an easy place to nest.
- Trails of large ants in and out of a cavity, crack or the root flare.
- Fine sawdust-like frass (wood shavings) at the base or in bark crevices.
- A hollow sound when the trunk is tapped near the activity.
Why it matters
The ants themselves are a nuisance — and a risk to your home if the colony expands toward it — but the bigger issue is what their presence implies. Internal decay weakens a tree's structure, and a tree with significant hollowing or rot is more likely to fail, especially under wind or snow load. The ants are essentially flagging a tree that deserves a proper inspection.
Carpenter ants are the smoke, not the fire. The fire is the decay they moved into — and that's the part worth checking.
Get the tree checked
If carpenter ants have set up in one of your trees, the right next step isn't ant spray — it's having the tree assessed for the decay that drew them. Book an assessment and we'll sound the trunk, gauge how much sound wood is left, and tell you whether it's a monitor, a prune, or a removal across Waterloo Region.