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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 Active Now

This article was published originally on 5/6/1992
Once again, it is a good spring for carpenter ants. Activity by these common, widespread and abundant ants is very noticeable in the springtime, as the wingless workers work (enlarge nests, forage for food, care for the larvae) and the winged swarmers swarm (fly off to start new colonies).

Control of carpenter ants remains a frustrating and difficult job. The easily-stated, straight forward theory of control is to put a small amount of household insecticide spray or dust directly into the ant nest. This would be much easier to do if the nests were conspicuous and easy to locate. Nests may be outdoors in stumps, logs, hollow trees, dead limbs or firewood and they may be a hundred feet or more from the house where the ants are invading in search or food. Nests may also be inside the house in sites as diverse as wall studs, window sills, wood flooring, rafters, roof sheathing and the interior spaces of hollow-core doors.

The standard 'tricks' for locating carpenter ant nests are:

  1. check areas of past or present moisture damage where ants are most likely to nest
  2. look for piles of coarse sawdust discarded from the nest
  3. patiently observe ants to see if you can determine where they are going to or coming from.
Carpenter ant foraging activity peaks at sundown during the spring, so the best time now to follow ants begins at dusk. Foraging activity in the summer peaks at sunup, and foraging by indoor colonies in the winter is highly variable with slightly more activity during the day.

Feed and Follow. A fourth option for locating carpenter ant nests is a modification of the third technique listed above. Instead of patiently observing random ant movements, it has been suggested you might have better luck with a 'feed and follow' procedure. Place a half-and-half mixture of honey and water in front of carpenter ant workers foraging in your house at sundown and wait for them to eat their fill. When full, they should return to the nest by a nearly direct route and your observation effort will be more efficient. Let me know if you try this and it works.

The alternative to treating carpenter ant nests directly is to use a residual insecticide into cracks, crevices and wall openings such as around moldings and electrical switches and outlets. Sprays will work in cracks and corners and along edges where ants forage. Dusts are preferred for application into walls. Drilling holes into wall voids between every stud is a technique advocated by a few pest control companies. There is little to suggest that this expensive treatment is any more effective than injecting dusts through existing openings and gaps. Similarly, monthly, year-long household treatment should not be necessary for carpenter ant control. See pamphlet IC-411, 'Carpenter Ants,' for additional information.

Carpenter Ants



This article originally appeared in the May 6, 1992 issue, p. 78.

Year of Publication: 
1992
Issue: 
IC-463(10) -- May 6, 1992