There are many species of ants in several different genera that can be found in and around the home. Most are little more than annoyances, though several species can also bite or sting when threatened. For the most part, though, ants are relatively harmless pests when compared to other insects, such as cockroaches. But one type of ant does pose a real problem in human homes—the carpenter ant (Camponotus spp.), which can do significant and expensive damage to buildings through its habit of boring out tunnels (galleries) in soft, decaying wood.
Carpenter ants are native to forest areas, where their habit of tunneling through rotten, fallen trees aids in the breakdown of dead timber. But if the same ants start tunneling in the softwood in a home, it will weaken the walls and cause major damage that can be costly to repair.
Identifying Carpenter Ants and Their Damage
Carpenter ants are typically 3/8 to 1/2 inch in length and black or brown in color. But while this is relatively large for an ant, the general description applies to many species of ants—size alone is not a good identifying feature. And because many types of ants will hide and nest in walls, it's often difficult to know if the ants you are seeing are a harmless species or carpenter ants that could be causing much more serious problems.
Carpenter ants are relatively easy to identify precisely under a magnifying glass, but it can be quite a challenge to catch and examine these quick insects. One way to do it is to flick one of the ants into a small plastic or glass container, seal it with a lid, then place the entire container in the freezer for a few minutes. When the ant is cold enough to get sluggish and slow, empty it out onto a plain surface and examine it under a magnifying glass. Look for two distinct characteristics:
- A smooth rounded back with no humps
- A single hump-like node at a very narrow, pinched waist
If you see these combined with a relatively large size, you will know you are looking at a carpenter ant. Once you've identified your suspect as a carpenter ant, you don't need to panic quite yet, as you could be witnessing a simple outdoor intruder rather than a worker from a colony eating away in your walls. These are signs that you're dealing with a true infestation:
- You will see carpenter ants frequently, over a period of several days or weeks.
- You may hear them inside walls, especially at night. The sound is sometimes described as a crackling noise and is caused by a large colony of ants gnawing at the decaying wood.
- You may see piles of sawdust (frass). Unlike termites, carpenter ants do not eat the wood they tunnel into, so they must get rid of the wood debris by piling it outside the openings to their tunnels or nests.
- Springtime may bring large numbers of winged carpenter ants, which leave the colony when it is time to mate. A few winged carpenter ants don't indicate an infestation in your walls, but a large number might mean a serious problem.
6 Ways to Get Rid of Carpenters Ants
Whether it is in your walls or in an outdoor tree or woodpile, you can generally locate the nests of carpenter ants by observing the well-defined trails of the foraging carpenter ants at dusk or after dark. The ants will be going in both directions, and those moving toward the nest may be carrying insects or bug parts for food. Finding this nest is crucial because eliminating just an occasionally traveling ant will do nothing for getting rid of the colony.
Once you identify the nest, you can use a number of approaches to get rid of these potentially devastating pests.
Replace Wet, Decaying Wood
Carpenter ants do not attack solid wood that has good structural integrity, so one way of getting rid of them is to root out and replace any weak decaying wood where the ants are tunneling. If the colony is in your walls, this will mean exposing the framing and doing the carpentry work necessary to replace the damaged wood. Any areas where plumbing pipes are running inside walls are places to examine, as the condensed moisture from cold water pipes is a major source of wood damage.
The process, which may involve a professional contractor, can be a major undertaking if the damage has been extensive. It involves removing interior wall surfaces or outer siding (or both) to expose wood framing, then replacing any framing members damaged by moisture and insects with new structurally sound wood.
Be aware that unless you also correct the sources of moisture causing the damage, carpenter ants are likely to return as soon as new moisture damage begins. And the wood replacement process can quite involved if the damage has seriously weakened load-bearing walls.
If the colony happens to be located in a tree, stump, or woodpile outside but near the home, eliminating that wood source will help eliminate the stray ants that are infiltrating your house.
Set Ant Bait
Minor infestations of carpenter ants can be dealt with using many of the same strategies used with other species of ants. The most popular ant control method is to use bait. Ant baits work by lacing a sweet substance with a substance toxic to ants, such as borax. Worker ants carry the borax-laced food back to the hidden colony inside the damaged wood, where it is eaten by other ants. Over a period of weeks, an entire colony can be killed in this way.
Borax is a naturally occurring mineral that works by interfering with the ants' digestive processes. As worker ants continue to carry the material into the colony, the entire group gradually starves to death. This process can take several weeks.
Inject Boric Acid Into Nests
Boric acid is a more concentrated form of the same borax that is used to lace ant baits. If you find the actual nest of a colony of carpenter ants, drill 1/8-inch diameter holes into the area where the colony is located, and use a bulb duster to squirt puffs of boric acid into the holes. In the same fashion as ant bait, the boric acid acts as a stomach poison. This is a method also used by many professional exterminators, but it can be difficult for homeowners since it requires precise identification of the colony and may involve repeated applications.
Use Diatomaceous Earth
Diatomaceous earth (DE) is a naturally occurring mineral made up of fossilized skeletons of diatoms, a form of algae. It is applied to ants in the same way as boric acid and works by the same principle. Powdered DE is puffed into holes drilled in the carpenter ant nest, where it breaks down the exoskeleton of the insects and causes them to dehydrate. Diatomaceous earth is an entirely non-toxic substance commonly sold as an organic garden pesticide. Its effectiveness depends on precise application, and perhaps repeated treatments, until a colony is eradicated.
Use a Pyrethrin-Based Spray
A more surefire remedy for carpenter ants is to spray a pyrethrin-based insecticide into the colony. Pure pyrethrin has fairly low toxicity since it is a natural product based on an extract from chrysanthemum flowers. Pyrethrin-based insecticides work by exciting the central nervous system of the insects, causing paralysis and death. But some insecticides blend pyrethrin with other chemicals, known as synergists, to increase their longevity and effectiveness. Such pesticides, often sold as pyrethroids, are not considered organic products, so they must be used very carefully, with safeguards against inhalation or skin contact. Pyrethroid chemical pesticides include those with names such as deltamethrin, cypermethrin, bifenthrin, or gamma-cyhalothrin.
As with most treatments, using a pyrethrin-based spray requires that you locate the nest, drill holes, then inject the spray into the colony itself. If the nest is correctly identified, though, this can be a very effective way to rid yourself of carpenter ants. If the carpenter ants still appear to be present after two weeks, repeat the treatment.
Pesticides based on pyrethrins are considered safe to use around humans and are among the least toxic of pesticides—but they are still neurotoxins and should be used with care. Pyrethrins are toxic to fish and other aquatic life, and they have been known to cause serious allergic reactions in humans, especially asthma sufferers. If accidental ingestion occurs, call a poison control center.
Call an Exterminator
If your infestation persists after various DIY remedies have been tried—or if you simply can't locate the carpenter ant nest—it may be time to hire a professional exterminator. The professional may try several of the same strategies, but will likely use professional-grade powders or sprays that are unavailable to homeowners.
The professional may also apply sprays using special equipment that creates an ultra-fine mist that penetrates wood more effectively than any method available to homeowners. Finally, a professional exterminator may apply perimeter treatments around the outside of your house in addition to addressing the nest itself. These perimeter applications may use residual pesticides that will kill any stray ants that attempt to enter your home in the following weeks and months, thereby preventing reinfestation.
What Causes Carpenter Ants?
Carpenter ants are drawn to any dead, decaying wood. The studs and other framing members in your home are natural targets, especially if they become wet and decay starts to set in. Homes set in wooded areas where other sources of dead, decaying wood are present can be especially prone to carpenter ants, especially if the home is built on a concrete slab or other foundation that is close to ground level where moisture can reach the sill plates and lower studs.
Carpenter ants do not actually eat the wood, but instead, hollow it out with an extensive network of tunnels in which to establish colonies. This tunneling gradually opens up the wood to more moisture, more rot, and more weakening.
Preventing Carpenter Ants
Once you deal with infestations in your walls, preventing new invasions of carpenter ants requires periodically inspecting wood framing and wood siding near ground level around foundations, and making sure to keep all gaps sealed. Inspect the penetrations where pipes and other services enter the home, as well as the sill plates where the walls meet foundation walls or slabs. Dry up leaks inside and outside the home, and repair any moisture-damaged wood when you find it.
Next, deal with sources of nearby decaying wood outside the home. Chip up any tree stumps and make sure the debris is removed or mulched in an area well away from the home. Firewood piles should be located well away from the house or garage. Trim away any tree branches so they do not touch the exterior walls or roof. Maintain a good clearance of at least 6 inches between wood siding and the soil line to ensure that siding does not wick moisture from the ground and provide ants with another route into the home.
Carpenter Ants vs. Termites
Carpenter ants are often confused with termites since both insects can cause substantial damage to the wood in a home's walls. Termites, however, actually consume the wood, unlike carpenter ants that merely tunnel through it, leaving behind residue (frass) in piles around the entry to the nest.
Termites can be distinguished from carpenter ants because they do not have the narrow, tightly constricted waists seen in the ants. Termite bodies are more cylindrical in shape, and they have straight antennae, not the jointed antennae seen in ants.
Where are carpenter ants found?
There are more than 1,000 species in the Camponotus genus, all loosely known as carpenter ants, but the one that is most prevalent is the black carpenter ant, Camponotus pennsylvanicus. This ant is native to the northeast and the central U.S., where it is found in nearly all forested areas. The black carpenter ant can currently be found in virtually all regions east of the Rocky Mountains.
While different types of carpenter ants can be found in almost all areas of the U.S., they are relatively rare in non-forested areas, such as deserts and high mountains. Carpenter ants naturally gravitate toward any source of wet, decaying wood. In regions where these ants are common in outdoor settings, problems can occur in any home where wood siding or framing is allowed to get moist and soft.
Do carpenter ants bite or sting?
Carpenter ants are large insects with strong jaws designed for tunneling through wood, and they can indeed inflict painful bites if they happen to latch onto the skin. This is not a common occurrence, though, as these insects are not blood feeders and don't go out of their way to bite.
Do carpenter ants fly?
Like many species of ants, those mating have wings and can often be seen flying in swarms during the mating season, which is spring and early summer.
Can you hear carpenter ants?
An established colony of carpenter ants often makes an audible crackling sound inside walls—the result of many individual ants simultaneously gnawing at the wood.
Carpenter Ants. University of Minnesota Extension, 2020.
Dominguez, Karen D. Is Borax Safe Around Children? National Capital Poison Center.
IPM for Ants. University of Nebraska–Lincoln.
Ramchandra, Atul M, and Peter J Victor. Pyrethroid Poisoning. Indian Journal of Critical Care Medicine, vol. 23, no. S4, 2019, pp. 0-0. Jaypee Brothers Medical Publishing, doi:10.5005/jp-journals-10071-23304
Pyrethrins. National Pesticide Information Center, 2014.
Black carpenter ant. University of Arkansas.