A pictorial key and guide to identifying 21 ant species in North America.

Authors: Tabatha Carroll and Gary Bennett

Ants have colonized every landmass on earth with the exception of Antarctica, and can be found in a variety of habitats, from forested areas to grasslands and various urban environments. They are pests in structural, household, industrial, garden and turf in urban environments. 

To control such industrious pests, we must know which ants are being dealt with, as well as where they nest, how they behave, and what they are feeding on. This information will be presented in this article along with an easy to use identification key (pages 86-87) to encourage correct identification of ants by pest management professionals. 

Ants of Greatest Importance. A review of the literature reveals 21 economically important species of ants that are in North America. (See table below). 

The 21 species of ants discussed on the previous pages were broken down into groups based on where they can be found as pests. Some species were placed in more than one group due to their ability to nest in a variety of habitats and therefore become a pest in multiple areas. Based on location, the following article includes Integrated Pest Management (IPM) practices as well as types of treatments that are useful for the control and elimination of the ant species described in the identification key. 

Indoor Nesting species. Species that can be found nesting within homes and other structures include the thief ant, Pharaoh ant, odorous house ant, crazy ant, ghost ant, white footed ant, Argentine ant and velvety tree ant. Many of these species can be difficult to control due to their small size and multiple satellite colonies. Cracks found in the foundation or exterior walls should be filled and sealed. Removal of debris around the perimeter or the home or building will discourage outdoor nests from relocating indoors. Sanitation efforts can decrease the amount of food and water they rely on (Granovsky & Howell, 1983). Most of these species will feed readily on sweet-tasting baits; however, the thief ant prefers a diet higher in protein so a protein bait should be used. Keep baits fresh and change baits when ant food preferences change. Avoid sprays because repellent response will result in ants spreading (budding).

Ornamental species.
 Species that are often pests of landscape or ornamental plants include the leafcutter ant, crazy ant, odorous house ant, Argentine ant, false honey ant, ghost ant, white footed ant and pavement ant. Unlike the other species mentioned, leafcutter ants cause physical damage to plants in landscapes and even can cause them to die due to stress by their constant removal of plant material. Plants should be treated with an approved insecticide to discourage cutting.

To limit the nesting sites, mulch should be no deeper than 2 inches and be placed at least 1 foot from the foundation of homes or other structures. This will also discourage species from relocating indoors. Any piles of firewood, stone, or other debris should be removed or lifted off the ground. Fewer objects lying around on the ground decreases the availability of preferred nesting sites. These species also can be controlled with baits. Avoid repellent sprays.

Slab/Sidewalk species. 
Species that can be found nesting under sidewalks or slabs include big headed ants, odorous house ants, cornfield ants, Argentine ants, fire ants and pavement ants. Due to their nesting habits, these species may occasionally invade indoors through cracks in the foundation in search of food (all but the citronella) or if heavy rains occur. Mating swarms also may emerge from foundation cracks. To discourage foragers from traveling indoors, stones should be avoided in landscaping as these species readily nest under them (Hedges, 1998). Cracks in the foundation or exterior of the structure should be filled and sealed. These species can be readily controlled with baits. If large colonies are present and are not responsive to baits, the use of power spraying equipment may be needed (Bennett et al., 2005). Follow label directions carefully.

Structural species. Pest species that nest within the structure and may cause damage to wood include acrobat ants, carpenter ants, velvety tree ants and little black ants. Velvety tree ants are included in this group, as they occasionally nest in attics or wall voids where moisture or rotting wood can be found in California. These species may be present if wood is rotting or if there is a water leak. If a nest is found, the area should be treated with a labeled commercial spray (Bennett et al., 2005). Rotten wood should be replaced and any leaks should be fixed (Hedges, 1998). Trees surrounding the structure should be trimmed back so they do not touch the roof or sides. Mulch in landscaping should be no greater than 2 inches deep and at least 1 foot from the perimeter of the foundation. Any piles of firewood or lumber should be relocated away from the structure. If foragers are found indoors, baits may be used as an effective control.

Turf species. Species found nesting in lawns and turf areas include Allegheny mound ants, field ants, fire ants, harvester ants and Argentine ants. These ants form large nests or mounds that are unsightly in lawns and turf areas. In addition, each species will defend the nest if threatened, resulting in bites and/or stings that are unpleasant. Mounds should be treated individually with a spray or a drench of a residual insecticide and checked regularly to ensure proper control (Bennett et al., 2005). There is also a variety of baits that can be effective against many of these pests.

Summary. Twenty-one species of ants are commonly found to be pests in North America. They affect a variety of areas, such as indoors, landscapes, ornamental plants, sidewalks and slabs, structural soundness, and turf and lawns. Practicing Integrated Pest Management by removal of debris, nesting sites, food and moisture are key factors in controlling pests in every situation. The addition of baits and residual sprays helps to ensure proper control.

Bennett, G.W., Owens, J.M., and R.M. Corrigan. 2010. Truman’s Scientific Guide to Pest Management Operations. 7th Ed. Cleveland. Questex Media. 229-254.

Granovsky, T.A., and H.N. Howell. 1983. A Practical Approach to Controlling Monomorium pharaonis (L.), Alias Pharaoh or Sugar Ant. Pest Management. 2(5): 11-14

Hedges, S.A. 1998. Field Guide for the Management of Structure Infesting Ants. 2nd Ed. Cleveland: GIE Media. 289 p.

Smith, M.R. 1965. House-Infesting Ants of the Eastern United States: Their Recognition, Biology, and Economic Importance. USDA/ARS Technological Bulletin. Washington, D.C. 1326.

Common pest species of ants

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A pictorial key and guide to identifying 21 ant species in North America