Carpenter Ants Infestation

William Kibbel III, The Home Inspector

Dear Home Inspector: Our house was treated for carpenter ants when we purchased it six years ago. We now have the large black ants in and around our home. I've heard that these ants don't really do any damage but I'm still concerned. Is this something we should expect in an old house? Do we need to have the exterminator come back and do another treatment?

carpenter ant
There are probably a lot more ants where this one came from.

This time of year (late spring) I get to see these insects, rather than only discovering evidence that they're somewhere in a house. Even in my own home, I've seen them scrambling across the kitchen floor in broad daylight.

I think there is some truth to the statement that carpenter ants don't really do any damage. At the very least, they aren't the originators of the structural damage to wood in buildings. Wood that has been damaged by these ants is likely to have been perpetually wet and decayed to some degree. Unlike termites, carpenter ants don't ingest wood, they're just hollowing out "galleries" for nesting. It's much more efficient and productive for them to excavate wood fibers that have been "tenderized" by water.

If you find a pile of coarse sawdust in or around your home, it can be a sign of an active infestation and that a colony has been established. This sawdust is the debris from the excavation for the nest. There are often parts of dead ants mixed in with the wood fibers.

Seeing the sawdust or the ants inside your home can certainly be disturbing. It may be a warning sign that water is damaging the structure. Before dealing with the ants, you need to deal with the source of the water damage. Some common locations of water damage include:

  • Near roof transitions or penetrations
  • Below clogged or leaking gutters
  • The bottom of door jambs
  • Window frames and sills
  • The sill plates on top of the foundation
  • The wood structures above damp crawlspaces
  • Near plumbing fixtures, particularly below tiled shower pans

ant damage
Clogged gutters are a common source of water damage, which in turn is an invitation to carpenter ants to invade your home.

After correcting any damp conditions or water leaks, it's important to remove and replace any wet, damaged wood. This deters ants from re-infesting and prevents further spread of the decay. Treating with some "miracle" product, or applying putty and painting over previously wet, damaged wood is not an acceptable permanent repair. It's also important to eliminate anything that makes it easy for the ants to enter the home. Any shrubs, ivy or other plants in contact with the walls should be removed. Tree branches near the walls or roof should be trimmed.

Even things outside, well away from the home, can contribute to a carpenter ant infestation. The main colony might not even be in the home. In fact, an inside colony may be just a satellite colony. Rotting tree stumps, firewood, a diseased tree or old landscape timbers could be harboring an army plotting an advance.

Since carpenter ants are only one of several types of wood destroying insects, it is important to work with a licensed pest control contractor to develop a plan of preventive strategies and chemical applications, if needed. For old-house owners, service contracts with an experienced exterminator that include annual inspections are a terrific value.

After discovering that single ant in my kitchen, I did a little investigating. I need to take care of my leaking porch roof, remove a dead tree and call our bug guy.

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