Carpenter Ants

Carpenter ant problems are notorious for being costly and difficult to solve. In the Pacific Northwest, most calls from homeowners to pest control companies are about carpenter ant problems.(1) Yet, there are straightforward ways to prevent carpenter ant problems in your home and avoid the need to use pesticides.

Carpenter ants “play a significant ecological role in forested ecosystems.”(2) A nest of carpenter ants can eat thousands of insects that would otherwise feed on forest trees. In turn, the ants are food for other creatures; a well-known animal that feeds on carpenter ants is the pileated woodpecker.(2)

If you see large black or red-and-black ants in your home (between 1/4 and 1/2 inch long) you may have a carpenter ant problem.(3) One of the first things you'll need to decide is if your guests are carpenter ants or if they are termites, insects frequently confused with carpenter ants. Here are four important differences:

You'll also want to make sure that you have more than just a few wandering ants. Sometimes ants will enter a house while they're out foraging; or queen ants will fly inside. “These occasional ants may not actually be causing problems,” according to Washington State University Extension.(5)

Carpenter ants do not eat wood. Most of their food is insects and honeydew, although they will eat household items like candy, honey, soda pop, and pet food.(6)

Carpenter ants often build a large “parent” nest and then add as many as twenty satellite nests.(4) The main nest requires moisture, so it will either be outside or, if indoors, near a leak or a poorly drained area.(5) Typically the parent nest is in decaying or rotten wood.(5) Often the parent nest is located in a tree or stump, while most indoor nests will be satellites. The ants maintain trails for travelling between the satellite nests and the main nest.(5)

Carpenter ants do not always build their nests in wood. They can successfully nest in insulation and paper.(3)

Carpenter ant colonies grow slowly. It takes between two and four years for a colony to grow to several hundred workers.(5) You have plenty of time to plan a successful, pesticide-free ant management strategy. A satellite colony started by a well-established parent colony can damage your house more quickly,(5) but you still don't need to rush into action.

You can prevent carpenter ant problems by taking some common-sense steps around your home:

Caulk cracks that ants could use to enter your house.(4)
Caulk around electrical and water lines where they enter your house.(5)
Trim branches near your house so that they aren't touching it. This keeps ants from using the branch as a “highway” into your home.(4)
Consider installing a gravel or stone strip around your house.(4)
Store firewood away from your house and up off the ground. You can build a woodpile on concrete blocks so its not touching the earth.(5)
Don't bring firewood into your house if its infested with ants.(3)
Don't feed ants. Store food in ant-proof containers.(4)
Clean clogged gutters to prevent water damage to your house.(4)
Remove logs, stumps, and waste wood near and under your house.(3)
Make sure crawl spaces and attics are well-ventilated.(5)
The wooden parts of porches and decks should not be in contact with the ground. Use concrete pier blocks underneath them.(5)
Make sure that window sills and door frames do not contact soil.(5)
Use a vapor barrier if you have a crawl space.(5)
Fix any leaks in the roof and plumbing pipes.(7)
Eliminate any damp conditions in or near your house.(4)
Replace any damaged structural wood in your house.(4)

The first step in solving a carpenter ant problem is to locate the nest. This involves a little detective work and is “often difficult but not impossible.”(5) Look for the sawdust that the ants create when they dig out their galleries. Listen for the sounds of the ants as they enlarge their nest. If your house has a crawl space, go under the house with a metal rod or a hammer. Tap all the structural wood and listen for differences in sound. When you hit the spot with the nest it will usually sound hollow. Typically a knife blade will easily penetrate the wood around the nest. You can also look for crawling ants and follow their trail back to their nest. Carpenter ants are most active at night, so a warm evening is a good time to look for trails.(5)

Once you've located the nest, you need to decide if its a satellite nest or a parent nest.(5) Most commonly, what you'll find inside your house is a satellite nest; a survey in Washington found that 75 percent of home carpenter ant infestations involved a satellite nest.(6) If your nest is a satellite nest, you'll need to locate the parent nest for most effective management.(5)

Depending on where your carpenter ant nest is located, you may simply be able to remove the nest once you've located it. If the nest has damaged structural parts of your house, repair the damage.(8)

If it's not possible to remove the nest, you can remove the ants (both adult and immature) from the nest with a vacuum cleaner. When you've finished vacuuming, be sure to dispose of the bag to prevent the ants from getting loose and returning.(3)

Researchers from Washington State University have calculated that vacuuming removes about 80 percent of the adults, and 60 percent of the brood (immature ants).(6) This means that you'll want to vacuum more than once.)

NCAP does not recommend the use of pesticides. However, we recognize that you or your pest control operator may believe that your carpenter ant problems require a pesticide treatment. If so, consider the use of boric acid or borate products. They can be applied as baits targeted to areas where ants are active, as paint-on wood preservatives in out-of-the-way locations, or as dusts inside wall voids. These techniques minimize exposure to people and pets. For information about the hazards of these products, see JPR 24(2):10-15 or www.pesticide.org/boricacid.pdf.

Avoid most carpenter ant pesticides, especially broadcast or perimeter treatments. NCAP has information about the hazards of many carpenter ant pesticides at www.pesticide.org.

Carpenter ants are difficult pests, but not impossible ones. The steps outlined in this article will help you protect your home from carpenter ant damage without using pesticides.

Successful Carpenter Ant Management without Pesticides