Northern Plains Integrated Pest Management GuideIPM

Authors: Ashley Mueller, Buyung Hadi

Ants are one of the most common pests that can be found in and around homes. Ants are social insects, and they live together in colonies. They are divided into three classes called castes: queens, males, and workers. Each caste serves the colony in specific way. Queens lay eggs and care for the brood; males play a vital role in reproduction; and workers provide food to the colony by foraging. Ants use pheromones to create invisible odor trails. The workers follow the odor trails to and from the nest while foraging for food. Indoors, ants are often seen following trails.

Although ants can be a nuisance, they can also contaminate food, wreak havoc on yards, and cause structural damage to buildings. There are many ways homeowners can prevent ants from coming indoors. Identifying problematic ants is essential in determining how an infestation is managed.

Identification

Adult worker

Odorous house ants are dark brown to black in color. The workers are about 1/8 inch in size. These ants are identified by the release of a pungent, cheesy odor when disturbed. These ants can be identified by the distinct trails they form when foraging for food often using guidelines like the edge of a building or a kitchen counter. Odorous house ants are a native species that occurs throughout the United States.

Habitat

Odorous house ants nest both outdoors and indoors. When outdoors, these ants typically construct shallow nests beneath nearly any object including stones, logs and fallen limbs, pavement, mulch in flower beds, and in plant cavities and refuse piles. Odorous house ants move often from nests that are not well built or if there is a weather change or disturbance.

These ants can be found indoors. The location of nests may be scattered, but they can be found frequently in walls and underneath floors. Areas with a high moisture content are especially at risk for the presence of odorous house ant nests.

Life Cycle and Seasonal History

Adults with scale insects

Odorous house ants typically have many egg-laying queens. The size of a colony varies according to age, and the number of individual ants can range from a few hundred to thousands. Eggs develop into larvae in 2 to 3 weeks; the larval stages last 2 to 4 weeks; and the pre-pupal and pupal stages typically take 10 days to 3 weeks. After several years, when a colony has matured, it may produce winged, reproductive colony members in late spring and early summer. Mating usually takes place in the nest or nearby, but occasionally reproductive flights have been observed. Inseminated females migrate with numerous workers to establish new nesting sites.

In regions of moderate temperatures, odorous house ant colonies forage for food throughout the year. Outdoor colonies become active and workers forage for food in the spring and continue through late fall. Foraging occurs during day and night.

Human Interaction and Urban Impact

Odorous house ants are not economically or medically important pests. Odorous house ants do not have the ability to sting. They are capable of biting, but due to their small size the bite is usually not painful. Redness, itching and mild swelling may accompany the bite. Any medical questions or concerns related to an odorous house ant bite should be directed towards a physician.

Odorous house ants are a common house and building invader, and they may nest indoors under floors or behind walls. Although a nuisance, odorous house ants do not cause structural damage.

Prevention and Management Approaches

Odorous house ants feed on sweets and meats, so foods should be kept in tightly sealed containers. Sites of food preparation should be kept clean, and trash cans into which food is dumped should be taken out on a regular basis. Recyclable containers should be rinsed well before storage. Potential openings into the house or building, such as a windowsill or under a door, should be sealed to prevent ant entry.

If an ant trail is observed indoors, the ants can be managed until a long-term solution can be implemented. If ants are going to a food source, it is recommended that the food source not be removed until after the ants are killed. Wiping a sponge dipped in soapy water over the ant trail kills the ants, and it is effective in removing pheromones. If the source of the ants is located, silica gel/pyrethrum can be applied in a small amount in the hole or crack. Boric acid or an inorganic desiccating dust may be used for residual control. Boric acid baits are available in sweets and protein food bases, making them attractive to odorous house ants.

If a high number of swarmers, ants with wings, are regularly found indoors, it is an indication of an indoor nest. An indoor colony of odorous house ants can be treated using various insecticides registered for home use. The key to effective odorous house ant management is eliminating the egg-laying queens and the colony members in the nest in addition to the ants seen. Choose a product that has this capability. Always use precaution and follow the label carefully before using any insecticide. Insecticides have a certain amount of toxicity to mammals; children and pets are especially at risk.