Now is the time of year many will be noticing carpenter ants in the home. These "large, black ants" are very abundant in Iowa and a common household pest. See pamphlet IC-411, "Carpenter Ants and Their Control" for drawings and details.
Ants found indoors during spring or summer could be invaders wandering in from outdoors or they may be foragers from a nest in the wall or ceiling. While there is no easy way to tell the source, it does pay to check carefully before making any treatment. If you determine the carpenter ants are coming from outdoors, see last year's newsletter for information on controlling carpenter ants in trees (HHPN, May 26, 1995, page 78).
Carpenter ant control can be a do-it-yourself project or a job for a professional pest control operator. Shop around and compare prices and services when selecting a pest control service.
Homeowners are limited to ready-to-use, household liquid or dust insecticides. Liquids include aerosol or hand-pump-dispenser residual products called "ant and roach killer" or something similar. Dust insecticides contain boric acid (for example, "Roach-Prufe"." See "Household Insect Pest Management" pamphlet, IC-472 for more information on using insecticides in the house.
Locating the source of carpenter ants is as important and as it is difficult. The best suggestion is to spend time observing ants to see if you can detect a pattern of movement. In spring and summer carpenter ants are more active at night and observations after sunset, with a flashlight on the outside and inside of the house may give an indication of the source.
Limiting insecticide application to direct nest treatment greatly reduces the amount of insecticide used and improves control. Carpenter ants usually nest in wood that has been softened by wood decay brought on by a moisture problem. Most likely sources of carpenter ants are window and door frames and sills, shower and tub enclosure walls, and kitchen and bath plumbing walls.
If persistent observation of the ants does not narrow down the potential treatment sites the alternative is to treat all cracks and crevices in the areas where foraging workers are abundant. This may reduce the population through gradual elimination of the foragers. As a rule, the practice of treating every wall void with a drill and dust treatment is of little benefit, especially if walls are insulated. And finally, homeowners who have tried them consistently report that ant baits do not work for carpenter ant control.
This article originally appeared in the May 10, 1996 issue, p. 74.