I have little piles of sawdust showing up uninvited in the house, does it mean I have carpenter ants?
Chances are good you have carpenter ants, though you might not always see obvious signs of damage. Unlike termites, carpenter ants cannot digest or eat wood and leave traces of sawdust behind; they eat honeydew, sweets, and other insects. They require rotting or compromised wood to build their nests. They are the largest ants we have in Montana, reaching one-quarter to one-half inch long (Fig. 1).
The most likely places to find carpenter ant nests are where wood has been wet and weathered, such as rotting wood or siding, under leaking areas, and wooded areas in contact with the soil. It’s common in Montana for the ants to get started in basements. Tapping the wood in suspected areas might reveal a nest from ants “rustling.” You can also probe the wood with a tool to look for ant galleries.
Carpenter ants are highly active at night. They move their colonies around frequently to keep the brood at the optimum temperature and often look groggy or disoriented. Carpenter ants (and other ant species) are often found in trees but are either searching for honeydew released from aphids or looking for habitat; they are not the culprits responsible for a particular tree declining.
The key to controlling carpenter ants is to locate and destroy the entire nest, particularly the queen. It is also critical to eliminate the source of moisture found around the house; otherwise, they are likely to re-infest the area.
Although a bit of patience is required, bait stations are a good control option. Baits may take weeks or months to work, as it takes a while to kill the workers and queen in the colony. Additionally, you can spray a band of insecticide around the outside foundation to knock down the worker ants during their travels. You can also apply an insecticidal dust to wall voids and in the boxes that house electrical outlets (both outside and inside), which are a frequent travel route for them. Make sure the insecticide is used according to the label, particularly if applying indoors.
Some tips for prevention include controlling moisture leaks, trimming back vegetation that is touching the house, sealing windows and openings, sealing wood before it is wet, and removing any ant-infested or water-damaged wood from the property. Also, stack firewood away from the house. A few carpenter ants around a home or building isn’t always a reason to panic; they might just be looking for food in the house when resources are limited outside. They also are a key resource in the environment, breaking down dead wood in outdoor areas.
For more information, please see the following resource:
Hansen, L. and J. Klotz. 2005. Carpenter ants of the United States and Canada. Cornell University Press. 224 p.