This article was published originally on 5/18/2011
One thing more disturbing than ant mounds in the prairie and pasture or in the lawn is ants in the house. Ants are one of the most common pests in and around homes, and one of the most common calls, messages and samples received by the ISU Plant & Insect Diagnostic Clinic. Although ants play a beneficial role in most environments, ants in the home and other buildings are undesirable because they may contaminate food, damage the structure or alarm residents simply by their presence.
There are approximately 8,800 different species of ants in the world. Only 700 different species are found in the U.S. and only a small portion of those have been documented from Iowa. Only 8 different kinds of ants are routinely encountered in or around homes and buildings.
Successful pest management begins with accurate identification. However, ants are notoriously difficult to identify. Most ants are small and hard to see without magnification (10X hand lens) and even the larger ants look alike to the untrained eye. A field guide to common ants on the Clinic website provides diagnostic drawings and descriptions of the 8 most common ants found in buildings in Iowa. Only worker ants (the wingless caste) are described.
Inspection is essential for determining where ants are a problem. Frequent observation or monitoring with sticky traps may help determine where ants are invading from outdoors, or where they are most active. If you are lucky the nest may be found by watching where the ants go; for some ants, such as carpenter ants, watch for activity at night. The best control comes when the nest location is known and treated directly.
Carpenter ants and other species enter homes from outside nests as they forage for food. For those species, exterior barrier sprays can be effective. Treat the perimeter and areas of activity or possible invasion, including thresholds, sills, the gap between siding and foundation, etc. Interior spray treatments can be used to decrease the foraging population, though the effect may be temporary unless application is made to, or close to, the nest location. Treat cracks, crevices, and voids in areas where ants are most active
Baiting is an easy treatment to make and reduces the amount of insecticide applied to kitchens and other areas where sprays are not wanted. Unfortunately, baits often stunt a colony rather than eliminate it and repeated application may be needed. Also, baits sold to homeowners have the added disadvantage of not being attractive to all ants. Most available baits contain sugar which is a good attractant for "sweet-feeding" ants such as odorous house ants, but will not be attractive to carpenter ants and grease ants. Baits should be placed as close to the source of ant activity as possible and in areas where no other foods are available to the ants, meaning cleanliness and sanitation are critical to bait success.
Links to information about specific ants:
Odorous house ant