THEM! -- Controlling Nuisance Outdoor Ants around the Home (07/01/21)
Ants in your lawn? Ants in your kitchen? Ants in your pants? Don’t despair! NDSU Extension Entomology has received several calls about nuisance outdoor ants this summer, which isn’t surprising given our dry conditions. So far, all complaints have involved ants in the genus Lasius, including ‘turfgrass ant’ and ‘cornfield ant.’ Both species are common and nest along gravel driveways, cracks in cement drives and walkways, between patio paver stones, and in lawns where the soil is exposed. They make small, crater-shaped mounds which are easily visible (see photo). They eat other insects and arthropods, and have an affinity for sweets. Ants can be seen tending aphids for their honeydew. Foraging workers sometimes enter homes in search of food, and if they find an indoor food source, the workers will leave chemical trails for other workers to follow. Food found either indoors or outdoors, is brought back to the nest to feed the colony. This behavior makes the use of ant baits an effective control measure.
To keep ants from entering the home, make sure the kitchen is clean and no attractive food, like a honey container, is left out for the ants to find. Use a mild vinegar solution to wipe down kitchen surfaces to remove ant chemical trails. Make sure doors, windows and other potential entry points are in good repair. Seal cracks and crevices where ants can enter.
Outdoors, these species rarely cause actual injury to turfgrass itself. The best strategy for lawns is to water regularly and mow at a height of three to four inches to encourage grass growth and discourage ant nesting. For chemical control of outdoor-nesting-ants, outdoor baits are the best option. Foraging workers find the bait, bring it back to feed the colony, and thus poison the entire nest including the queen. Several brands are available to homeowners in either liquid or granular formulations. Most liquid baits contain boric acid (borax) which acts as a stomach poison. Follow the instructions on the label for bait station use and placement. Outdoor liquid baits are best for treating smaller areas. Some granular bait formulations contain hydramethylnon, which inhibits metabolism. Granular baits can be used to treat larger areas, but are rather expensive and should not be watered, as water will break down the bait more quick than it normally would. When using baits, do not use any other insecticides around the baits because the ants will be inhibited from getting to the bait. It may take up to a week before you start to see results when using baits. It may seem at first that it would be easier to control the giant nuclear-irradiated mutant ants from the 1954 sci-fi thriller THEM!, but be patient - baits work well and you won’t have to use a flamethrower.
Other insecticide options include broad spectrum granules, which can be applied as a barrier around the home or as a lawn application, depending on the product. Keep in mind that broad-spectrum insecticides may have negative consequences for non-target, beneficial insects such as ground-nesting bees, so please try the non-chemical and baits first, and only use a broad-spectrum lawn application as a last resort. Barrier sprays also can be made to prevent ants from entering the home. When using any pesticide, be sure to read, understand and follow the directions on the label.
Research Specialist, Extension Entomology