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Ants in the House

- Several species commonly enter houses in search of food and water -

Summary: A number of different ant species invade homes, especially kitchens, in search of food and water. A few species can even nest in walls and ceiling. Most of the time these ants do little damage but should be controlled because some nests can become very large and bothersome.

Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)

Nuisance (house) ants

Certain ants, for example fire ants and harvester ants, attract our attention because they can sting people and animals. Some, like carpenter ants, are important because they damage building materials. And some ants only become pests when they enter homes in search of food and water.

The last group of ants usually causes no structural damage, and pose little health risk, but are important because of their numbers alone. These are the house-invading ants, nuisance ants or simply house ants. Common house ant species are: odorous house ant, Argentine ant, pharaoh ant and a few other species.

Most ants that invade homes are yellow, red, brown or black in color, constricted at the waist, and 1/8-1/4" long. If you find ants that are larger than about 3/8" (in the US) you've probably found carpenter ants. You may also occasionally see ants with wings (all species), these are the so called "reproductives".

ants attracted to liquid ant bait

Worker ants feeding on a drop of ant bait. Ants consume the bait and take some back to their nest where it disrupts the colony. Photo by E.A. DeAngelis.

Other common names: sugar ants, moisture ants, sweet ants.


Ant control in houses

While house ants generally cause no direct damage they can become a nuisance if the nests get too large. The safest, and best approach to ant control is to use baits. Baits pose little risk and most are relatively inexpensive. There is no need to apply insecticide sprays for these pests. In fact, insecticide sprays often disperse colonies and make matters worse (see below).

Use baits NOT sprays to control ants

Baits are a food that is attractive to worker ants that may be laced with a slow-acting insecticide. Workers locate bait and carry some back to the nest where it poisons the colony. Insecticide sprays are not effective because most can be detected and avoided by foraging worker ants.

How baits work

Baits work best because they target the colony. Ants are social insects and live in highly organized colonies. This social organization allows ant colonies to grow very large but if the colony is disrupted the ants will die. Baits work by disrupting these complex colonies, often killing the egg-laying queen in the process.

See Ant Control and Ant Baits for additional information.


Control of Common Nuisance House Ants With Baits

(1) Place baits near ant activity, do not contaminate area with insecticide. You can initially place a plain, sugary bait (no insecticide) to train workers to the placement. If ants appear to be feeding on bait, as in photo above, replace plain bait with one laced with insecticide. For small infestations use ready-made, or home-made, liquid boric acid baits. But, for large, stubborn infestations use commercial gel or granular baits, both are available here (DoMyOwnPestControl.com).

(2) Replace individual stations when they are exhausted or completely consumed.

(3) Within a week the number of ants should be significantly lower.

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Jack DeAngelis, PhD,  , email:  [email protected]

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