Odorous house ants (OHA) are difficult to control. Unfortunately, they are becoming more common in samples sent to the Insect Identification Lab. These small (1/8-inch) dark ants form distinct trails along outdoor and indoor surfaces.
Description & Nesting Sites
OHA are mistaken for pavement ants, which can readily be controlled with most baits. The most accurate diagnostic difference, visible under magnification, is the absence of a noticeable node or “bump” along the constricted area between thorax and abdomen of the odorous house ant. Pavement ants have two obvious nodes, and fine grooves or striations along the head and thorax. Pavement ants also are more likely to displace bits of soil from their typical nesting location under sidewalks, driveways, and other paved areas. OHA emit a rotten coconut or pine scent when crushed.
OHA will nest in virtually every imaginable location. Outdoor sites include under pavements, stones, mulch, woodpiles, flower pots, and house siding. They may forage indoors for food and moisture. Nests also occur indoors within wall cavities, appliances, etc., especially near sources of moisture. The nests tend to be mobile; colonies relocate fast and often in response to changes in weather and disturbance.
OHA colonies tend to have numerous, egg-laying queens and the primary colonies may split into smaller ones for no apparent reason. Ants foraging indoors feed on all manner of foods, ranging from the trash can to the cereal bowl.
OHA is difficult to control, especially by homeowners.
- The better baits to try are often syrupy ones, such as Combat® Ant Killing Gel or Terro® Ant Killer II.
- As with all ants, activity indoors can sometimes be reduced by removing ready access to food and moisture (water leaks, spillage, trash cans, pet food dishes, etc.).
- Temporary relief can sometimes be gained by wiping away the invisible odor trails with a kitchen cleanser or mild detergent. Do not disturb foraging trails, however, if you are using bait.
- Caulking obvious ant entry points also may be helpful, along with trimming back shrubs and limbs touching buildings. In nature, this ant feeds extensively on plant nectar and honeydew excreted by plant-sucking insects such as aphids.
When OHA are the problem, homeowners may be better off calling a professional, although they, too, are challenged by this ant. Some products used by professionals can be effective but are not available to the general public.
By Mike Potter, Extension Entomologist