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Horticulture and Home Pest News
Horticulture & Home Pest News is filled with articles on current horticulture, plant care, pest management, and common household pests written by Iowa State University Extension specialists in the Departments of Entomology, Horticulture and Plant Pathology.

Carpenter Ants

This article was published originally on 6/16/1993
'Large black ants' have become the most common topic of discussion for callers to the Extension Entomology office during the past week. Apparently, wet weather over the past year and a half has been favorable to the carpenter ants and their numbers have increased with a corresponding increase in the numbers of workers and swarmers invading homes. The following are answers to some of the most common questions.

Are you sure these are carpenter ants? If the words "large, black ants" describe your specimens, then yes, they are probably carpenter ants. For further proof of identification, look for the evenly rounded thorax pictured on carpenter ant pamphlet, IC-411.

Are the ants with wings also carpenter ants? Probably, if they are large, black, winged ants. Winged ants are swarmers; that is, members of the colony produced as reproductives (kings and queens) for the purpose of flying off and starting new colonies.

Is moisture and wood decay always necessary for carpenter ant nesting? No. Carpenter ants usually nest in moist wood such as inside hollow trees, dead limbs, logs, stumps and firewood, and in structural wood exposed to water from leaks or condensation (window and door frames and sills, shower and tub walls, and kitchen plumbing walls, roof sheathing and rafters, and so forth). Nests may be in sound timbers, dry cracks and joints, existing cavities such as hollow doors, or even in foam insulation.

Can I treat carpenter ants myself or should I hire a pest control operator? It depends. Carpenter ant treatment is most effective when the nest is located and treated directly. You may actually have more time, patience and opportunity to locate the nest than will a PCO. On the other hand, the PCO has experience and special application equipment that improve the chances of successful control. If you do hire a PCO, check around and get more than one cost estimate. Prices for carpenter ant control vary from $25 to $1000. The latter treatment includes a drill-and-dust application to every wall void in the house, whether the walls are insulated or not, and whether ants are likely in those walls or not. It also comes with a recommendation for monthly treatment for a year.

How can I treat for carpenter ants? Begin by trying to locate the nest. This is easier said than done, but the effort pays off. Look at both indoor and outdoor sites, and look at night when foragers are most active. Look for ant trails or a general direction of movement or feed foragers small dabs of honey and then follow them to the nest. If necessary replace damaged or decayed wood at the infestation site and correct moisture problems.

Homeowners can treat with 'ant and roach killer' insecticide sprays or boric acid dust. Treat wall voids and other hidden spaces where ants are entering by spraying the liquids or puffing the dust into cracks and gaps or through small drilled holes if necessary. Dust applicators may be available in a hardware store or you may resort to a plastic squeeze bottle with a narrow tube or tip (an old cafe ketchup bottle, for example). If you can not locate the nest, make a general application of spray or dust to cracks, crevices and room edges where ants are most numerous. Dust can be injected into wall voids via the holes surrounding electrical outlets. Use extreme caution around electrical wiring. Spraying outlet openings is not recommended.

Outdoor nests can be directly treated with turfgrass insecticides such as diazinon or Dursban or barrier treatment around the house foundation can also be used to prevent foraging ant entry.



This article originally appeared in the June 16, 1993 issue, pp. 1993 issue, pp. 95-96.

Year of Publication: 
1993
Issue: 
IC-465(15) -- June 16, 1993