Structural and Public Health Pests: Carpenter Ants

Pest Management In and Around Structures October 13, 2009 Print Friendly and PDF



Carpenter ants play important roles as decomposers of decaying trees and can become damaging pests when nesting in structures. Unlike termites, carpenter ants do not feed on wood, they simply nest there. Wood is damaged as these ants construct smooth "galleries". with rounded edges, excavated in softer parts of wood building elements. Galleries tend to follow the grain of the wood, with passages that cross harder wood.

Water-damaged or other softened wood is typically conducive to nesting, with gallery expansion into adjacent sound wood as the colony grows. Nest may also be constructed in wall voids, insulation, hollow doors or wood furnishings or fixtures.

Carpenter ant nests are kept clean, with frass, sawdust-like wood shavings, dead ants and other debris pushed out of the gallery through a crack or slit, creating tell-tale dump piles that look like sawdust from a distance.

Carpenter ants will eat fruit, vegetation, insects, meat, grease, fat and sugars including insect honeydew. Carpenter ants typically forage in late afternoon and night, up to 100 yards from the nest, and will carry food back to the colony.

Table 1
Carpenter ant species most likely to become pests in school environments.

Common and species name Geographic distribution
Black carpenter ant, Camponotus pennsylvanicus Throughout the US.
Red carpenter ant, Camponotus ferrugineus Throughout the US.
Smaller carpenter ant, Camponotus nearcticus Throughout the US.

Monitoring and inspection for carpenter ants

Carpenter ants forage outside the nest for food and water and are often sighted in infested dwellings around sinks or bathroom fixtures seeking water. Foraging ants can sometimes be followed to locate the nest, which may be outside of the structure. If this is the case, they do not require any action.

Sawdust-like waste piles, slits or windows, are also telltale signs of nesting activity. An awl, spatula or screwdriver can be used to probe for damaged wood. Thermal imaging can also be used to locate potential nests within a building.

Cultural and physical options for carpenter ant management

A primary defense against carpenter ants is to avoid moisture-damaged wood. This can be done by regular inspection and prompt correction of roof, window or vent leaks, clogged, damaged or improperly aligned gutters or wood that may be in contact with soil, vegetation, firewood piles or other debris that prevents proper drying. Similarly, decaying or softened wood building elements should be repaired or replaced including soft decking or window or door sills.

Remove tree stumps adjacent to structures. Trim branches touching structures, or touching wires leading to structures, to reduce transit opportunities for carpenter ants and other pests and improve air circulation and drying. Improve ventilation to speed drying in attics, crawlspaces and other enclosed areas.

At-risk wood that is low to the ground, in shaded locations or otherwise prone to moisture can be designed or replaced with insect-resistant woods including cedar, cyprus or jarrah.

Non-chemical controls include removing infested wood and vacuuming up ants, nests and debris. Heat treatment and freezing are also potential controls but rarely used.

Table 2
Commonly used products for physical, cultural or mechanical management of carpenter ants and their uses.

Type Example Products Uses
sealants many Seal potential entryways, seal seams where floor meets baseboard to prevent moisture damage to wood.
structural repair many Replace damaged wood with sound, dry wood or a non-wood substitute.
vacuum Remove individual ants.

Pesticide options for carpenter ants

Containerized baits and liquid or gel baits placed in inaccessible areas reduce potential for exposure. Containerized baits or reusable bait stations can be placed near ant trails. Liquid or gel baits can be placed in cracks or crevices adjacent to trails or nests. Baits may take up to 60 days to eliminate the colony. Replenish baits as needed until ants are no longer present.

Dusts may also be applied in a manner that greatly reduces exposure potential, including into voids reached by removing electrical outlet or switch plate covers, or in holes drilled in infested wood and sealed after the application. Applications of residual-active pesticides to exposed, human-contact surfaces on the interior or exterior of structures, and use of Danger or Warning-label pesticides, are typically not needed and should be avoided. In addition, barrier applications to exposed impervious surfaces including foundations, walkways and driveways are prone to runoff into surface water and should be avoided.

Table 3
a. Insecticides carrying a CAUTION label or exempt from EPA registration, in formulations that reduce potential for exposure.

Active ingredient Example products Uses
abamectin Prescription Treatment® Advance Granular Carpenter Ant Bait 499-370 Granular formulations which can be placed into voids or into reusable bait stations to reduce potential for exposure.
hydramethylnon Prescription Treatment® Advance Granular Carpenter Ant Bait 499-370 Same as above.
boric acid, orthoboric acid Niban® FG 64405-2 Intice® Ant Granules 73079-2 Same as above.
boric acid, orthoboric acid Drax® Liquid Ant Killer II SWT 9444-206 Intice™ Ant Gel 73079-1 Solution or gel that can be applied as drops in inaccessible areas. Wipe up any over-application.
borax Terro® Ant Killer II 149-8 Same as above.
disodium octaborate tetrahydrate Bora-Care® Injectable Concentrate 64405-4 Injected into infested wood, reducing potential for exposure.

b. CAUTION-label or exempt formulations with greater potential for exposure.

Active ingredient Example products Uses
disodium octaborate tetrahydrate Boracide® 64405-7 Nibor® 64405-8 Timbor® 64405-8 Dust formulation. To reduce exposure hazard, use only in voids that will be sealed after use or apply to surfaces in inaccessible areas. Wipe up any over-application.
sulfluramid Prescription Treatment Advance® Dual Choice Ant Bait Stations 499-459 Same as above
boric acid Prescription Treatment® 240 Permadust® 499-384 Pressurized aerosol formulation. Boric acid will leave dust residual. To reduce exposure hazard, use only in voids that will be sealed after use or apply to surfaces in inaccessible areas.

c. CAUTION-label formulations with greater potential for toxicity and/or exposure.

Active ingredient Example products Uses
deltamethrin Delta Dust® 432-772 Dust formulation. To reduce exposure hazard, use only in voids that will be sealed after use or apply to surfaces in inaccessible areas. Wipe up any over-application
bifenthrin Talstar® One 279-3206 Sprayed or otherwise applied to surfaces. Spray applications with repellant insecticides such as pyrethroids can contaminate an area and make baiting ineffective until the residue degrades. To reduce exposure hazard and avoid contamination, use alternative formulations and/or limit applications to non-volatile active ingredients applied to non-human contact surfaces in inaccessible areas.
chlorfenapyr Phantom® 241-392 Same as above
cyfluthrin Cykick® 499-304 Same as above
cypermethrin Tempo® SC Ultra 11556-124 Demon® EC 100-1004 Same as above
disodium octaborate tetrahydrate Bora-Care® 64405-1 Nibor® 64405-8 Timbor® 64405-8 Same as above
deltamethrin Suspend® SC 432-763 Same as above
imidacloprid Premise® 2 Insecticide 432-1331 Premise® 75 Insecticide 432-1332 Same as above
lamda-cyhalothrin Demand® CS 100-1066 Same as above

Priorities for carpenter ant management.

  • Research
  • Efficacy of bait formulations.

Additional resources for carpenter ant management

Arizona Cooperative Extension. 2004. Ants. Pest Press. (PDF)

Collman, S.J., L. Hansen, R. Akre and A.L. Antonelli. 2008. Carpenter Ants.

Hahn, J., C. Cannon and M. Ascerno. 2002. Carpenter Ants. University of Minnesota Cooperative Extension.

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.