Threats to Trees

Carpenter Ants

The carpenter ant (Camponotus pennsylvanicus) is a social insect and lives in colonies.  Carpenter ants, unlike termites, do not eat wood.   They nest in wet wood in the cavities of trees.   They are black in colour and large in size, about 8-11 mm in length.  Carpenter ants are more of a nuisance than a serious pest.  Their presence is usually an indicator of wood decay.  They are most active at night when they feed on insects, fruit, garbage and the honeydew from aphids.

Carpenter ant
Frass from Carpenter ant damage
Capenter Ant tunnels as seen in a cross section of infested tree.

Hosts and Damage

Any tree with decayed wood can be a nesting place for carpenter ants.  Only the decayed wood is affected in living trees, not the healthy, sound wood.

Workers make galleries by chewing moist wood to provide more room for the expanding ant colony.  The chewed wood is ejected through the nest entrance where it forms a pile and is a sign of their presence.  This sawdust-like frass is easily visible outdoors, but may be hidden within wall voids indoors.  Carpenter ants make rustling noises, loud enough to hear through walls in buildings.

Carpenter ants are frequently found nesting in damp wood in buildings.  Structural wood may decome damp from leaking roofs, plumbing or around window and door frames.

Outdoor sites that support carpenter ants include uncovered firewood, remnant stumps and living trees with decay, logs or wooded building materials, wooden structures such as fences, porches, decks, retaining walls or buildings.

Specific Management Practices for Control of Carpenter Ants

If you have carpenter ants in the tree:

  • Check for the presence of carpenter ants on and around trees when the weather is warm.  They do not always nest in the tree.  Very often they are just searching for food (insects, honeydew from aphids, debris, etc.)
  • Look for the frass (sawdust-like particles) around the tree base, left by the carpenter ants.
  • Locate possible nesting places in the tree.  This is usually directly above the ejected frass in the decayed wood at wounds and cavities.
  • Since the carpenter ants nest in damp and decayed wood, their nest in a tree indicates the presence of wood decay.  Wood decay could potentially result in structural failure (stem or limb breakage).  Trees with a carpenter ant nest may require pruning or removal.


If you have carpenter ants in your home:

  • Look for the frass left by carpenter ants.  Keep in mind that the frass could be hidden in wall voids and may not be easily visible.
  • Place something sweet (honey or jam) in an area that ants frequent.  Then follow them to determine where they are nesting.
  • Listen for the sound of ant activity within wall voids, using an inverted glass or a stethoscope if possible, in the late afternoon.   Concentrate on areas known to contain damp wood.
  • Repair all leaking roofs, plumbing and drains to eliminate damp wood in the building.
  • Replace any rotting porches, fences, or wood structures around your house.
  • Store firewood or lumber above the ground if it is kept outdoors.


Chemical control of carpenter ants:

  • Set out boric acid or sodium borate based baits as close to the nest entrance as possible. These products are available at most garden centres and hardware stores.   Follow the instructions on the label.

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