The Q&A Archives: Carpenter Ants

Question: Carpenter ants, what is the best way to eradicate them ?

Answer: If the nest is located in a wall void, it is best to dust directly with bendiocarb (Ficam), boric acid or Diazinon. Drilling 1/4 or 3/8 inch holes into the wall, sills or joists, where the nest is located, will best help the insecticide penetrate. Treat three to six feet on either side of where ants are entering to hopefully contact the nest. Some drill a series of holes at 12-inch intervals in infested timbers to intercept cavities and galleries of the nest. Holes can later be sealed by putting in dowels as plugs, small corks or covering with an appropriate sealant and touched up with paint, leaving no visible damage from the repairs. Spraying or dusting the baseboards or cracks and crevices around the infested area with residual insecticides, without locating and treating the nest, usually does not give complete control. Foraging workers will contact the insecticide and die while ants staying inside the galleries of the nest, along with the queen and developing larvae, may not be greatly affected. Kill might be slow with only crack and crevice treatment since workers need to carry enough insecticide on their feet back into the nest. Ants in the nest can live more than six months without feeding. However, aerosol spray treatments in the nest can be effective if much insulation is present. Vapors may be spread to penetrate inaccessible areas of the nest, aiding in colony eradication. Approaches and areas adjacent to the nest must be thoroughly treated with residual insecticides such as chlorpyrifos (Dursban) or Diazinon (Knox Out). Outside the structure, all breaks where ants can enter the home must be treated, and a perimeter spray applied against the foundation wall at least two feet up and three feet out. Be sure to treat under the lower edge of sidings, around window and door frames and the chimney flashing.

There are many insecticides labelled for ant control. Before using an insecticide, always read the label, follow directions and safety precautions.

Restricted Use Pesticides, available for the licensed pest control operator or applicator, would include bendiocarb+ pyrethrins (Ficam Plus) cyfluthrin (Optem, Tempo), cypermethrin (Cynoff, Cyper-Active, Demon, Vikor), deltamethrin (Suspend), lambdacyhalothrin (Commodore), permethrin (Dragnet, Flee, Prelude, Torpedo), propetamphos (Safrotin) and tralomethrin (Saga). Outdoor Use only would include fenvalerate (Tribute) and fluvalinate (Mavrik, Yardex). Other labelled materials are acephate (Orthene), ammonium silica gel (Drione, Tri-Die), bendiocarb (Ficam), boric acid (Borid), borate (Bora-Care, Drax, Mop-Up, Niban, Perma-Dust, Tim-Bor), carbaryl (Sevin), chlorpyrifos (Duration, Dursban, Empire, Engage, Killmaster II, Tenure), chlorpyrifos + pyrethrins (Dual Use), diatomaceous earth (Answer), diazinon (Knox Out), esfenvalerate (Conquer), propoxur (Baygon), pyrethrins (Exciter, Kicker, Microcare, Pyrenone, Pyrethrum, Safer, Synerol, Uld, X-Clude), resmethrin (Vectrin), sulfuramid (Pro-Control), and sumithrin (Steri-Fab).

Bait and granular formulations are usually not highly effective against carpenter ants. Dusts, wettable powders, injections, and sprayables are better. It is often best to employ a licensed pest control firm, especially where nests are hard to find. Some firms attempt to locate the nest or nests and treat only in suspected places. Others drill and dust potential nesting sites. Most apply a perimeter spray treatment around the house foundation. Avoid simply spraying each month whenever ants are seen. Infestations will continue unless nests are eliminated. Locating the nest is not always easy, but is essential for control.

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