Some of the industry’s most serious ant pests have extremely large populations, many nesting sites and queens distributed throughout these nesting sites. Here’s how to treat these “super pests.”
Not all ant colonies are created equal. Some colonies are neat congregations of ants in compact nests that can be controlled easily while other colonies are particularly troublesome and appear to have nests scattered over a wide area in many different habitats. It is these latter colonies that are challenging to pest management professionals and to homeowners.
Identification of the pest ant and knowledge of its biology is important to determine if the infestation can be eliminated or should be monitored and treated for a longer period of time (Klotz et al, 2008). This might be considered “control” of the ants as opposed to “management” of the ant population.
All ants share the familiar features of having a queen (or queens) to reproduce plus a worker caste responsible for foraging for food and caring for the queen and brood. Usually it is the workers that invade homes and become either a nuisance to the homeowner or a structurally damaging pest.
Ants live in a nest or nests where the queen or queens are located with the workers and brood (eggs, larvae and pupae). The recommended approach to control ants is to find and treat the “nest” (Hedges, 2010). If the colony occupies more than one nesting site, control becomes challenging.
Some species of ants have nuptial flights at specific times of the year that readily identify the pest species. Carpenter ants with spring flights and moisture ants with their flights in later summer readily identify these groups. But many ants lack or have only minor flights. If ants do not reproduce by flying, other means of reproducing colonies must occur. People unintentionally become ants’ best friends as they assist in transporting queens and colonies. Ants are transported when people move potted plants from homes, natural areas, nurseries or other commercial establishments. People also transport ants in firewood, railroad ties, landscaping timbers, lumber, wood scraps, etc. (Photo 1, below right). Ants are moved through commerce directly in products or accidentally through crates and packaging materials.
A carpenter ant colony has a main or parent nest with the queen, workers, brood and often winged forms. This nest is often located outside the structure in a damp wood environment to allow for brood development. In addition, carpenter ants seek sites for satellite nests to rear older brood and winged forms. These may be in warmer, drier areas in nature or inside structures in voids, attics, crawlspaces or other sheltered areas. Satellite nests contain workers and brood but not a queen. Ants will travel between the main nest and the satellite nests during the various seasons. Eliminating the parent nest will eventually also eliminate the satellite nests because these do not contain a reproductive queen. Carpenter ant colonies are monogyne, that is, they contain only one queen (Hansen and Klotz, 2005).
In contrast, some colonies of our most serious ant pests may be described as having “super” colonies because of their extremely large populations, many nesting sites, and queens distributed throughout these nesting sites.
One group of related ants includes Argentine ants, odorous house ants and velvety tree ants that belong to the subfamily of ants called Dolichodorinae. These ants can form extremely large colonies because they have multiple nesting sites (polydomy) and many queens (polygyny). Winged females generally mate within the nest although males may fly between nests. Many nests reproduce by budding or are transported from one site to another by human activities.
The Argentine ant (Linepithema humile) (photo 2) is an exotic ant that was introduced into North America in the late 1800s and has become an important pest through the southern half of the United States. Additionally, it has become established in recent years in the urban areas of Puget Sound in Washington State and in British Columbia.
Odorous house ants (Tapinoma sessile) (photo 3) and velvety tree ants are native ants but have many of the characteristics of exotic or tramp ants in that they are easily transported through human activities, have many queens, and have many nesting sites. Odorous house ants have become a serious pest throughout most of the country.
Velvety tree ants are chiefly found in the western states and southwestern Canada. Two species, Liometopum occidentale and L. luctuosum (L. occidentale shown in photo 4) nest in wood and in foam insulation and are considered structurally damaging. In nature these ants are found in the heartwood of standing trees and in dead trees and stumps. They are generally found in softwoods such as pine, cedar and fir, but L. occidentale has also been found in deciduous trees.
Proper identification of these ants may possibly be confused because of the similarity of size and color. These ants are brown to black in color and between 3-5 mm in size. Although they are monomorphic, the size of workers within one colony can vary by 2 mm. One species of velvety tree ant (L. occidentale) has a dark red mesosoma (middle section including the thorax).
Argentine ants and velvety tree ants have a distinct upright single node whereas the single node of odorous house ants is flattened at the pedicel (connection between the mesosoma and gaster). Both species of velvety tree ants and odorous house ants have a pheromone the ants release when alarmed or crushed that smells like rotten coconuts. The odor of Argentine ants has a rancid smell that is more difficult to recognize.
Nests of these three dolichoderine ants are established oftentimes in temporary areas: under a piece of wood, beneath pine tree needles and cones, in a wall void, under scrap lumber, beneath yard ornaments and toys, etc. These nests are moved or relocated as conditions change in the weather or the environment. Changes include the movement or disturbance of materials, disruption of trails, introduction of new foraging sites or changes in food sources.
Size of nests may vary from a few hundred to several thousand. Ants are nonaggressive to ants from the same colony even though many nesting sites have been established by a single colony. Weather conditions may encourage these nests to move into structures where they become problematic for the homeowner. Ants are attracted to available moisture and food inside structures when limited on the exterior. Cold seasonal changes cause ants from nesting sites to clump together and form fewer nesting sites (Buczkowski and Bennett 2008).
The term “sugar ants” has been applied to not only these ants but to many ants because most ants require carbohydrates. In addition the brood requires protein for development. The choice of foraging sites for these ants is honeydew from aphids or other homopterans that are feeding on vegetation. These insects suck the juices from plants where they feed on all parts of the plants. Ants are capable of foraging on other available food, if honeydew is not available and in the dormant season, these ants overwinter in structures and may be attracted to sweet materials.
In winter months, foraging activity decreases, development of brood is slowed, and ants may seek shelter in structures where they forage for moisture and food with the higher temperatures indoors. The metabolism of the ants is low and their susceptibility to chemicals is reduced. Plus, the fact that there may be any number of nests within the structure, each with their own queens, makes control difficult. If one nest is destroyed, ants from another untreated nest may migrate into that void.
The number of queens and nesting sites varies. As the foraging sites for the ants change, the nests or parts of the nest are moved closer to the foraging sites. This is called dispersed central-place foraging (Bennett and Buczkowski 2006). Nests also will be moved with changes in the environment: temperature, moisture or other disturbances (Toennison 2009). These sites may include inside structures because of disturbances in their natural nesting areas or because of climatic changes or lack of foraging. These movements can be sudden with large numbers of ants involved. Nests have been relocated in some cases overnight or over a weekend into kitchens, into electric equipment such as computers, printers or other office equipment (Photo 5).
Another ant colony, the pavement ant Tetramorium caespitum, that has many queens and many nesting sites, shares many of the features described previously. These ants have nesting sites under sidewalks, driveways, slab construction, foundations and rocks used in landscaping materials. They are also about the same size and color as Argentine ants, odorous house ants and velvety tree ants. The pavement ants, however, have two nodes plus a stinger and nuptial flights midsummer. Their many nests throughout the yards around structures can be troublesome for control and these ants will seek food and water inside structures, particularly in the late winter and early spring.
Strategies to monitor, manage and eventually control ants with multiple nesting sites include several options. Of prime importance is the proper identification of the pest ant (Hedges, 2010). Inform the client about the life history of the pest ant. Controlling ants with multiple nests may require more than one treatment as nests may be moved into areas where other nests were eliminated, particularly if foraging sites are available.
Integrated Pest Management can be applied by the elimination of foraging sites, trails and structural entrances followed by chemical application. Strategies may include the combination of any of the following:
- Vegetation control around the structure; prune or trim trees, shrubs, flowering bushes and plants touching the structure.
- Monitor fences, wires and cables that provide avenues for foraging ants between the structure and vegetation.
- Clearance of soil, decorative bark and vegetation around the foundation so that 5-6 inches of the foundation is clear to allow monitoring of ant trails and entrances into structures.
- Exclusion of entrances into the structure used by ants that can be filled with caulking or other materials.
- Chemical control can be offered through a menu of options that include gel baits, liquid baits, granular baits, interior application of sprays, perimeter sprays, or combinations of spray applications and baits. Check the LABEL of baits and sprays for the proper directions and cautions.
The author is an instructor in the biology department at Spokane Falls Community College, Spokane, Wash. Email her at firstname.lastname@example.org.
Buczkowski, G. and G. Bennett. 2006. Dispersed central-place foraging in the polydomous odorous house ant, Tapinoma sessile as revealed by a protein marker. Insectes Sociaux 53: 282-290.
Buczkowski, G. and G. Bennett. 2008. Seasonal polydomy in a polygynous supercolony of the odorous house ant, Tapinoma sessile. Ecol. Entomol. 33: 780-788.
Hansen, L.D. and J.H. Klotz. 2005. Carpenter ants of the United States and Canada. Cornell University Press, Ithaca, N.Y.
Hedges, S.A. 2010. Field Guide for the Management of Structure-Infesting Ants, 3rd Ed. G.I.E., Cleveland, Ohio.
Klotz, J., L. Hansen, R. Pospischil, and M. Rust. 2008. Urban Ants of North American and Europe: Identification, Biology and Management. Comstock Publishing Associates, Cornell University Press, Ithaca, N.Y.
Toennisson, T.A. 2009. Suburban ant community structure with emphasis on Tapinoma sessile and T. sessile colony movement in the laboratory. Master’s Thesis, University of Tennessee.