Carpenter Ant Control

- Carpenter ant nests in buildings should be treated to limit potential damage -

Summary: Carpenter ants nests in structures can be controlled by creating an insecticide barrier around the building that ants must cross in order to forage for food and water. This barrier can be placed inside exterior walls and/or on the exterior foundation (perimeter). It is not necessary to locate the colony or colonies inside the structure itself.

Jack DeAngelis, PhD

OSU Ext. Entomologist (ret.)

The standard treatment to control carpenter ants is to apply insecticide into exterior wall voids, completely around the structure, thereby creating a barrier that worker ants must cross to forage for food. Wall voids are the spaces between wall studs that are usually filled with insulation, ants use these avenues to enter and exit the structure. Wall void treatments generally require drilling into these spaces and may be beyond the ability of most homeowners.

Perimeter sprays are often used alone or in conjunction with wall void treatments for added protection. Typically, a perimeter treatment involves spraying an insecticide such as Termidor Insecticide (see Termidor For Carpenter Ants) around the base of the structure where the siding overlaps the foundation (see photo right).

The third, and newest tools, are carpenter ant baits. Baits designed for carpenter ants may be used around the base of the structure or indoors (see Using Carpenter Ant Baits).

House foundation (grey), siding (white), and foundation vent (black). "Perimeter" sprays should be applied where the siding overlaps the foundation, under the lip of the siding and completely around the house. Photo by JD DeAngelis.

There is no need for periodic maintenance treatments, often recommended by pest control companies, nor is it necessary to locate the carpenter ant nest. Treat only when ant activity is detected during regular inspections.

Avoiding carpenter ant damage

(1) Inspect exterior of structure at least once each year during warm months, morning or evening. Look for large ants moving into or out of the structure often in more or less single file lines.

(2) Remove all vegetation in contact with structure to at least 12" away. This ensures that you will be able to see any ants that are moving into or away from the structure. Ants will also use vegetation to "bridge over" any perimeter treatment that is applied. Be sure to also check above for overhanging branches that touch any part of the structure.

(3) If a carpenter ants are found treat exterior wall voids and/or apply a perimeter insecticide. Wall voids can be treated with a number of different insecticides. Sodium borate dust (see Using Timbor Insecticide) is a low toxicity choice. You may need to hire a pest control company to do the wall void treatment because it involves drilling into these spaces.

(4) Finally, treat the perimeter (perimeter treatment) where the house siding overlaps the foundation with an insecticide register for this application. Termidor Insecticide is currently labelled for this use (see Related Articles below). You can do this treatment yourself or have the pest control company do it as the last step.

(5) Treat only when active carpenter ant infestations are found. Periodic maintenance treatments are not necessary.

Related Articles

+ Carpenter Ant Identification and Colony Growth

+ Using Termidor Insecticide as a Perimeter Treatment

+ Using New Carpenter Ant Baits

+ How to Inspect for Structural Pests

+ Other Wood Damaging Insect Pests

+ Rules for Selecting an Exterminator

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