Gaining Control of Structure-Infesting Carpenter Ants

Carpenter ants are one of the most common structure-infesting ants in the United States. Although they infest homes, their foundational parent colonies are normally established outdoors in tree holes, downed trees or limbs and similar situations where there is wood that is very wet.

MOVING IN. When they move into a home, carpenter ants may establish secondary nesting sites, also called satellite colonies. They can use dry wood for nesting, but they usually start in wet or partially rotted wood and work from there. They are not likely to establish a parent colony indoors unless there is a constant supply of moisture, such as a plumbing leak.

Some species of carpenter ants can cause significant structural damage to the wood in homes when they decide to build their nest in the structure’s wood framework, but not all species use the wood in buildings for nesting. Many species are basically nuisance pests that usually nest outdoors and may come indoors incidentally to find and establish feeding or watering sites. They also may nest opportunistically indoors in existing void spaces in building materials, foraging for food and water and generally disrupting the peace.

Carpenter ants do not eat wood, but rather use it as we do to build their homes. The tools of their trade are their powerful mandibles, which they use to tear off small bits of wood and create large, clean chambers, customizing their new home to fit their needs. As they do this, the small bits of wood are deposited outside the construction zone, usually on floors or windowsills. This sawdust-like material, along with the other trash they generate, consisting mostly of insect parts from their lunch and less fortunate teammates, is called “frass” and accumulates outside of the nest area. The ants probably wouldn’t want you to know this, but the location of frass is key to identifying them and then finding and destroying their nest.

IDENTIFICATION. The most reliable physical features that will help verify that the ants you are looking at are carpenter ants are a smoothly rounded thorax when viewed from the side and a single, large, peaked node that connects the thorax to the abdomen.

The least reliable features are color and size. Most carpenter ants found in homes are polymorphic. That means there are many sizes of worker ants ranging from small (1/3 inch) up to 1 inch in length. The workers of some carpenter ant species are all the same size, or monomorphic, and are much smaller (1/4 inch) than the ants that are polymorphic. Although the most common house-infesting carpenter ant species, Camponotus pennsylvanicus, is solid black, other species may be brown, black and brown, reddish, red and black or other combinations of colors.

Customer reports of carpenter ants can range from “I keep seeing a few dead ants every day” to “What is this sawdust that is always on the floor?” to “I am seeing these huge ants crawling all over my house.” Sometimes the report will be of swarming, winged ants coming from a windowsill or crawling around the house. A brief conversation with your customer can usually clarify when and where the ants or their evidence are appearing. Often, if the customer can accompany you as you inspect, they may remember additional helpful information. This also gives you a chance to point out and discuss things around the structure that may be working in favor of the ants.

Locating at least a few ants during your inspection can help you verify the species of the ants in question. One of the most common causes of ant control failure is not determining the species you are trying to control. The behavioral habits of carpenter ants are significantly different from other ant species, so determining the species is crucial to developing a proper treatment plan.

GAINING CONTROL. Once you have determined that carpenter ants are in play, your next steps will be critical in gaining control as quickly as possible. Do not be tempted to reach for the carpenter ant bait or your favorite spray and start treating everywhere you have seen ants or their evidence at this point. Your inspection is not yet complete.

Primary carpenter ant colonies often contain several thousand worker ants, and their numbers are usually underestimated. This is probably because carpenter ants are much more active at night, when they go unnoticed. Inspect the entire house, including the attic and crawlspace, if present, and all outdoor areas to find any piles of carpenter ant frass, exit holes above the frass and live or dead ants. Remember that carpenter ants sometimes carry their frass several feet away from the nest site, so this is not always a good indicator of the nest location.

If you are not seeing definitive evidence of a satellite colony, there may not be one. The ants may be coming in from an outdoor colony. As mentioned earlier, carpenter ants are more active at night. A good flashlight inspection of outdoor areas just after dark is a good investment of your time and often will save you many follow-up trips by revealing where the parent and satellite nests are located.

It is amazing to see what happens outdoors just after dark when carpenter ants are in the area. Often, within a few minutes of darkness, foraging trails will appear consisting of thousands of ants making their way across the yard, coming out of trees and climbing walls. Follow these trails in both directions to find entry points and feeding sites on one end and the nest on the other.

We found a satellite nest in a second-floor window frame this way. There were hundreds of ants leaving the slightly rotted windowsill on the outside of the house that had not been observed during daylight hours, even a few minutes before dark. They were the source of many indoor sightings that had caused several additional trips to the house for the technician.

TREATMENT. Once nests are located, they can be treated directly with a non-repellent dust. It often will be necessary to drill into the galleries with a 1/8-inch drill bit to get the dust into all areas. Sometimes, ants will come out of the galleries in large numbers during treatment. They can be removed with a vacuum.

Carpenter ant baits can be highly effective when placed along active nighttime ant trails. Non-repellent sprays also can also be used around the perimeter of structures and for direct contact treatment on outdoor trails as product labels permit. Some situations may be better suited to one type of treatment and others to a combination of treatments. In the case mentioned previously with a satellite nest in a second-floor window frame, we returned the next day for ladder safety reasons to drill and treat the nesting area with a non-repellent dust. Drill holes were sealed and daily ant sightings in the home ended.

Carpenter ants are not likely to infest a home unless conditions are favorable for survival. Because of their colony size and physical size, carpenter ants have a relatively high demand for moisture, so plumbing leaks, environmental moisture intrusion or other continuous sources of moisture such as condensation in walls or crawlspaces must be corrected.

Gutters should be inspected closely to make sure they are installed correctly and drain properly. Harborage for parent or satellite carpenter ant colonies outdoors such as firewood piles stored too close to the home, dead trees, stumps or dead limbs in the trees or yard should be addressed as well. It is also critical to block or seal entry points which may help ants get into the structure. Inspect caulking around doors and windows, pipe penetrations around air conditioning equipment, and door sweeps, and make sure windows are closing properly. Tree limbs touching the roof or walls may allow ants to reach the building without interacting with your perimeter treatments.

FINAL STEPS. The last step in an effective carpenter ant control program is to follow up with the customer soon after the service visit to make sure the problem is fully resolved. An outdoor area favorable for carpenter ants can support many colonies, so it is not unusual to find more than one. Follow up may consist of a phone check-in with your customer, a quick visit or one more evening inspection with a good flashlight, depending on the severity of the infestation and sensitivity of the customer.

Effective carpenter ant control is a challenge that requires a concise, directed approach based on our knowledge of their biology and habits, but it can be very satisfying to accomplish as we help protect our customers from these persistent wood-destroying pests.