WSU Extension

Pestsense

Carpenter ants

(revision date: 5/4/2022)


Use Integrated Pest Management (IPM) for successful pest management.

Biology
Carpenter ants are large ants and can be 1/2 inch to 1/4 inch in length. They are black or red and black in color. They are a pest because they commonly make nests in homes. Carpenter ants do not eat wood, but they will excavate it for nesting and occasionally cause structural weakening. They will also nest in insulation. A carpenter ant colony can have two kinds of nests. The parent nest with the queen, eggs, larvae, and workers, is usually located outside away from the house in a stump or log. A satellite nest may form when worker ants move into a house. Satellite nests do not have a functioning queen and can not reproduce. Many home infestations are satellite nests. Carpenter ant mating swarms generally occur from April-early June.
Management Options

Non-Chemical Management
  • For most successful management, do not create conditions conducive to infestations.
  • Avoid dense shrubbery around homes (includes tree branches touching eaves).
  • Beauty bark around foundations can hide ant trails and allow for easy travel.
  • Remove stumps or rotting logs near houses.
  • Avoid wood-soil contact.
  • Ensure good ventilation in crawl spaces.
  • Do not place woodpiles next to house.
Select non-chemical management options as your first choice!

Chemical Management
IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides

In heavily wooded areas you may have to apply preventative treatments 2-3 times during April/May, mid-July, and perhaps again in Sept/Oct. Because carpenter ants are a structural pest you may need to contact a pest management professional.

If you choose to use a pesticide, some examples of products that are legal in Washington are listed below. Some products are labeled for just INDOOR or just OUTDOOR use, or may allow both uses. Be sure to choose a product appropriate for your situation. Always read and follow all label directions.
  • Bonide Termite & Carpenter Ant Killer Conc
    Active ingredient: permethrin  |  EPA reg no: 4-349
  • Combat Source Kill Max A2 Fast Killing Formula
    Active ingredient: fipronil  |  EPA reg no: 64240-42
  • Orthro Bug B Gon Insect Killer/Lawns and Gardens R-T-Spray
    Active ingredient: Bifenthrin, Zeta-cypermethrin  |  EPA reg no: 279-9535-239
  • This list may not include all products registered for this use.
Images
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Caption: Carpenter Ant Worker
Photo by: Art Antonelli