Because these insects live in hidden nests, it’s important that you don’t immediately start killing the first carpenter ants you see inside your home. The first step is to locate the nest so that you can destroy the colony.
Finding the Nest
As soon as you see carpenter ants in your home, follow them. As these ants walk, they lay down scent trails that allow other ants to follow them to and from food sources. You may need to be patient and follow them back to baseboards, cabinets, doors, or other wooden structures. You may even need to follow them outside if they’ve nested in tree stumps or dead trees.
However, even if you have an ant problem, you might not always see actual ants out and about. If this is the case, you may need to lure them out with some sweet bait, like diluted honey or sugar milk.
Carpenter ants are nocturnal, so set the bait out at night and then wait. When you get to the suspected area of the nest, listen closely—you may be able to hear a faint rustling sound. You can also tap on areas of suspected nests to listen for hollow sounds of damaged wood.
Killing the Ants
Once you’ve located the carpenter ant nest, you have several options for extermination.
The most common solution is to use an insecticide that contains pyrethroids. The trick is getting insecticidal spray or dust into the nest. You should never spray liquids around electrical outlets or junction boxes, but insecticidal dust can be used in these areas.
You can spray into any existing crevices, but you’ll probably need to drill additional holes into the voids in walls or hollow doors to access the colony. When using pesticides, always follow the instructions on the packaging. Also, only apply it to nests—killing individual worker ants won’t make a dent in the problem.
Boric acid dust also kills carpenter ants on contact, and it may be safer and easier to get into tiny spaces. Boric acid dust should be available at most hardware stores, and you’ll typically use an included applicator to puff the dust into holes or crevices.
Ant baiting is another possible solution, but it takes a bit longer to work. You simply apply the poisoned bait along the ants’ walking paths for them to pick up and bring back to the nest. There are special baits for carpenter ants, as generic ant baits might not be effective. Even so, ants can be picky, and if they ignore one type of bait, you may need to try another.
Desiccants are products that kill insects by destroying the outer protective layer of their bodies and causing them to dehydrate. Only licensed exterminators can apply silica gel, but diatomaceous earth is another common desiccant that anyone can purchase. It’s non-toxic to people and animals, but make sure not to breathe in any of the fine dust, which can cause lung damage. You can apply it into nests the same way you would an insecticidal dust.
Both diatomaceous earth and boric acid are non-pesticidal ant killers. If you do an internet search, you’ll find results claiming that all manner of essential oils or household products “repel” carpenter ants. Even if this is true, you don’t want a repellent at this stage of an infestation, as the ants will likely just relocate within your home or property, probably to a harder-to-treat location. You need to kill off the colony within your home before you concern yourself with repelling ants.