Successfully manage carpenter ants by using the 3 i’s

By |  April 26, 2017

Successful carpenter ant management comes down to “interview, identify and inspect.”

Carpenter ant nest in firewood Photo: Dr. Laurel Hansen

Carpenter ant nest in firewood
Photo: Dr. Laurel Hansen

Yes, those big black ants come every spring, but then they disappear!

This homeowner comment is common — and should alert the technician that there is a problem with carpenter ants (Camponotus spp.) at the account. The main nest may be on the outside of the structure, and satellite nests may be established within the structure. Both nest types will excavate wood in constructing nesting sites for brood. A perimeter spray may provide immediate results, but a comprehensive management strategy for carpenter ants includes a three-step process to enhance the application of chemicals.

1. The interview is usually the first contact with the customer.

A telephone conversation or comment on a general pest inspection should trigger additional questions, such as:

  • “Did you see the ants last year, and/or in previous years?”
  • “Do trees in your yard touch the roof or side of the structure?”
  • “Have you had any recent roof or gutter repairs, or plumbing leaks?”
  • “Have you recently had trees removed?”
  • “Have you had wind damage to the structure or to trees?”

One answer may lead to additional questions, and the scope of the problem may be initially determined in preparation for management.

2. Next, identify the specific ant problem.

Carpenter ant nest in railroad tie Photo: Dr. Laurel Hansen

Carpenter ant nest in railroad tie
Photo: Dr. Laurel Hansen

There are a number of ants that will invade structures for food, water and/or nesting sites. While carpenter ants vary in size, color, and nesting requirements, all workers have a single node and a terminal, circular anal orifice fringed with hairs. All workers are easily recognized by the evenly convex thoracic dorsum in profile. There are 24 species of carpenter ants in the United States and Canada (Hansen and Klotz, 2005). Dependent on species, nesting sites vary from sound wood to decayed wood, from attic areas to crawlspace areas. Color will vary from all black to red-and-black to orange-and-brown, depending on species. Workers will range in size within a colony from the large major, or soldier, with the large head to the small minors with narrower heads.

Depending on the species, carpenter ant workers vary in size from the larger species at 0.25 to 0.5 in. to the small species at 0.14 to 0.3 in. in length. Technicians should be familiar with the species that are common in their areas, and also determine whether other ant species are involved in an infestation.

3. Performing a detailed inspection of the structure and surrounding area will determine management strategies.

Excavated sawdust from carpenter ants Photo: Dr. Laurel Hansen

Excavated sawdust from carpenter ants
Photo: Dr. Laurel Hansen

Knowledge of the biology and behavior of carpenter ants will facilitate the inspection. Carpenter ants do not eat wood, but they excavate areas in wood to expand their nesting sites and interior trails. This can lead to structural damage with the growth of a colony.

Carpenter ants will forage on a variety of food — including insects in the vegetation around the structure. During early spring in infested structures, the ants also may be attracted to moist areas around kitchens, laundry rooms and bathrooms for water. They may feed on sweets such as syrup, fruit or candy before food is available outside the structure.

One of their more common food sources is honeydew from aphids during the foraging season. Vegetation should be inspected for the location of carpenter ant foraging arenas. Ants trail to these sites along fences, wires, foundations, landscaping timbers, and irrigation equipment such as garden hoses. Ants also will create their own trails through lawns, landscaping materials and underground roots. Although ants will forage throughout the day, foraging activity peaks at sunset and extends into the twilight hours.

With the knowledge of carpenter ant biology and behavior (see “Ants aren’t always evil”), an inspection will provide suggestions and tools for management. Inspection of the structure and surrounding area can provide information regarding possible nesting sites for a parent, and satellite nests.

On the exterior, look for conducive conditions such as vegetation in contact with the structure, wood in contact with the soil, firewood stacked next to the structure, and inadequate foundation clearance below the siding. On the interior of the structure, close inspection should include ventilation problems in the crawlspace or attic, evidence of former plumbing or moisture leaks, and extruded sawdust. Carpenter ant excavations of wood may be present in protected areas such as closets, unfinished basements or attic areas. Carpenter ants will follow guidelines within the structure such as pipes for plumbing or electrical wires through wall voids. Excavated material may be present at these sites under sinks, behind electrical wall outlet coverings, or light fixtures.

Treatment strategies

A carpenter ant trail through vegetation Photo: Dr. Laurel Hansen

A carpenter ant trail through vegetation
Photo: Dr. Laurel Hansen

Ant management ideally would include the location of the parent nest and all the satellite nests. When this is not possible, direct your attention toward eliminating conducive conditions such as moisture problems through proper ventilation, vegetation in contact with the structure, and wood in contact with the soil. Close inspection also will reveal foraging sites for ants in vegetation and trails between parent and satellite nests and foraging arenas.
Bait can be placed in areas on the interior

where ants frequent such as under sinks, refrigerators or other appliances where ants have been observed. Dust formulations can be effective in drywall voids where satellite colonies nest or trail.

Perimeter sprays, particularly those materials that feature transfer ability, can be applied to the exterior of structures and to trails where it is permitted on labels. Perimeter sprays should be directed where the foundation meets the soil, away from the foundation by at least 12 in., and under the lower edge of the siding where ants often trail to locate entry points into the structure.

Carpenter ant management can be challenging, but with an interview from the client, proper identification, comprehensive inspection of the property, and knowledge of carpenter ant biology and behavior, the tools for management can be applied with a greater measure of success.


Hansen, L.D. and J. Klotz. 2005. “Carpenter ants of the United States and Canada.” Cornell University Press, New York.
Hansen, L.D. and A. Antonelli. 2010. “Identification and habits of key ant pests of Washington.” PNB 624.
Hedges, S.A. 2010. Field Guide for the Management of Structure-infesting Ants. GIE Media, Richfield, Ohio.

Contributor Dr. Laurel Hansen is a biology instructor at Spokane Falls (Wash.) Community College, and a member of the PMP Hall of Fame (Class of 2015). You can reach her at

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