Small ants are a common pest in the home kitchen or bathroom. Foraging ant workers may appear a few at a time over a broad area, or a large number may descend on food, refuse, pet food, or moisture available overnight. Of the dozen different ant species that may be a nuisance inside the home in Iowa, the typical small, house-invading species are pavement ants (https://hortnews.extension.iastate.edu/pavement-ant) and odorous house ants. (https://hortnews.extension.iastate.edu/odorous-house-ant)
Ready-to-use household insecticide sprays are a convenient method for treating ants in the house. Unfortunately, sprays may impact only the small portion of the colony – those workers looking for food. Queens and other colony members safely hidden in their nests within wall voids, behind cabinets or appliances, or in door and window frames are not affected. When the nest location cannot be determined or is inaccessible, insecticide baits are a good option for control.
Types of Ant Baits
Liquid and gel baits are often the most versatile and effective control options for small household ants. Ant baits contain a food attractant (usually sugar) combined with a slow-acting insecticide. After foraging worker ants find the bait, they transport it back to the nest and feed it to the queen(s) and other colony members. As a result, the entire colony can be destroyed.
Baits come in pre-filled plastic stations, bottles, plastic tubes or syringes. Popular consumer brands include Combat, Raid, Ortho, and Terro. Active ingredients include sodium tetraborate decahydrate (borax* at ~5%), thiamethoxam (.003%), avermectin (0.01%), indoxacarb (.05%), or fipronil (0.001%). These chemicals have little to no toxicity to people, pets, or wildlife at the concentrations contained in the ready-to-use products. As with all pesticides, read and follow label directions and keep them away from children and pets.
How to Use Ant Baits
Place the baits next to wherever ants are seen, such as in corners and along walls. Through patient observation, you may be able to discern a trail that worker ants follow between food and the nest. Baits placed beside ant trails are often the most effective.
Containerized baits (trays or dispensers) can be placed on the surface where ants are active. For liquid or gel baits in bottles, plastic tubes, or syringes place a small drop or dab of bait on the top (non-sticky side) of masking tape, wax paper, or small pieces of the product packaging.
Keep counters and floors clean by sweeping and washing but do not use cleaning agents or insecticides around the baits. Do not place ant bait directly on surfaces that have been previously treated with insecticide. Sprays and cleansers may deter ants from approaching and eating the bait and carrying the bait back to their colony.
Baits take time to work. Best results occur when ants feed over a period of time, not just a brief visit by a few ants. Replenish the bait in sites with high activity as needed. Activity may decrease after an initial "feeding frenzy" of ants around the bait. Watch for additional ant activity and place baits wherever ants are seen. It can be tempting to kill ants that come to the bait. The baits only work if the ants consume the bait and also return to the colony, tolerate the increased ant activity to allow the bait to work. Carefully discard uneaten bait and wash surfaces of any remaining residue with soap and water.
When Ant Baits Don’t Work
Ants can be finicky in their food preferences at different times throughout the year. Try several brands of bait to find one that the ants will accept. If one bait product isn't attractive or doesn't seem to be working, try another.
Unfortunately, not all ant species can be controlled with sugary baits described above. General ant baits are rarely effective against tiny grease ants, large black carpenter ants (https://hortnews.extension.iastate.edu/carpenter-ant) or soil-nesting field ants (https://hortnews.extension.iastate.edu/field-ant). Modified or special bait products or residual insecticide dusts or sprays may be needed to control these ants in and around the home.
*Borax is not the same ingredient as boric acid. Boric acid (pH 5.0) is produced by reacting borax with an acid. Borax is alkaline (pH 9.3).
Adapted from ENTFACT-619, Ant Control for Householders by Michael F. Potter, University of Kentucky.