[Ant Control Issue] Native or Invaders?

Features - Cover Feature: Ant Control Issue

As protectors of clients’ home, health and property, PMPs should recognize new pest ant species. If ants are not readily recognized, every attempt should be made to make a positive identification.

April 30, 2013

In January 2012, the National Pest Management Association (NPMA) completed a nationwide survey of pest management professionals (PMPs) regarding treatments for ants. Only bed bugs ranked as being more difficult to control. Ants were treated by 100 percent of the companies that participated in the survey. The most common ants treated were carpenter ants (66 percent of the companies), odorous house ants (62 percent) and pavement ants (59 percent). Six other species were treated and the number varied from 20 percent to 36 percent. Another question asked in the survey was: “Do you feel the incidence of ants in your region is increasing, decreasing or remaining the same?” Results revealed that 54 percent thought the incidence was increasing, whereas 41 percent thought it was the same and only 5 percent indicated the incidence was decreasing.

Questions not asked in the survey: “Are you experiencing ‘strange’ new ants in your area?” “If so, have you identified the ants?” As different ants vary in their life cycles and foraging behavior, management of ants is dependent upon proper identification. If ants are not readily recognized, every attempt should be made to make a positive identification. As protectors of clients’ home, health and property, PMPs should recognize new pest ant species. Communication with regulatory and association groups alert others regarding the possible establishment and eradication of introduced species.

In two other surveys (Canada and Pacific Northwest), “tramp” ants were collected. These are defined as ant species with small, sterile workers distributed by human commerce and living in close association with humans. Tramp ant colonies have many queens, are unicolonial (non aggressive) and usually reproduce by budding because they have a small or reduced nuptial flight. These ants are often transported with vegetation shipped or moved in containers with soil and previously were not found in an area.

Commoners or Native? From the NPMA survey, the most often treated ants were carpenter ants, odorous house ants and pavement ants. These ants will be considered with management suggestions followed by a select group of “tramp” ants identified in the Canadian and Pacific Northwest surveys.

Carpenter ants, Camponotus modoc (left), and  carpenter ants excavating wood on railroad ties (right). Photo: Laurel Hansen

Carpenter ants (Camponotus spp.)
Carpenter ants belong to the Family Formicinae, characterized by a single node and the production of formic acid. This group of native ants includes 24 species in North America that are wood destroying or nuisance pest ants. Workers of carpenter ants are polymorphic (many sizes) ranging from the large majors to the small minors. Carpenter ants nest in wood either inside the structure where satellite nests are generally found or on the outside where the parent nest is most often located in dead wood near the home or in nonliving parts of trees. Colonies of these ants have a single queen contained in the parent nest and when mature several satellite nests. Carpenter ants forage on honeydew from aphids and on other insects. The natural habitat for carpenter ants is forested regions, but they also are found in urban areas where there are trees. Colonies may live for many years.

Management. Inspection includes a thorough investigation of the infestation to determine nesting sites on the exterior and in the interior. Vegetation in contact with the structure should be removed to eliminate foraging activity. Inspection for possible entry points should include fences, landscaping timbers and other guidelines where ants are trailing.

Chemical treatment may include a perimeter spray application and/or baits. For perimeter treatments follow label directions. Perimeter sprays should be directed under the lower edge of the siding where it overlaps the foundation and along the exterior foundation wall. Baits should be applied on trails, where ants are entering the structure, or at foraging sites.

Swarming flights occur in the spring. The appearance of winged forms emerging within the structure because of the warmer conditions is particularly troublesome. These winged forms do not respond to bait and do not encounter perimeter treatments. Application of dusts to areas where winged ants are emerging may be required.

Workers that become troublesome in the early spring before foraging activity occurs outside will be attracted to a gel or liquid bait. Most activity occurs in bathrooms or kitchens because ants are attracted to moisture.

Odorous house ant, Tapinoma sessile. Photo: AntWeb.org

Odorous house ants (Tapinoma sessile)
Odorous house ants belong to the Family Dolichoderinae, have a node reduced to a flat “button” and do not sting. This is a single native species where workers are the same size (monomorphic). The colonies are polygynous (many queens) and their nesting sites are described as being opportunistic, that is the nests are constantly being moved and workers will congregate to shelter brood under boards, playground equipment, boxes, leaves or whatever is available. Nests are shallow and relocated about every three weeks during the summer months. Many queens are scattered among the colony nesting sites. Ants may overwinter within wall voids in structures, particularly in cooler climates. Odorous house ants are so named because of the production of a putrid coconut-like odor caused by the release of butyric acid from anal glands. Occasional flights have been observed in late spring, but most new colonies are established by budding. Workers forage on honeydew and other sweet materials, but are often attracted to food items indoors.

Management. As with carpenter ants, inspect for vegetation in contact with the structure. All vegetation touching the structure should be eliminated. Follow label directions to treat with perimeter sprays or with baits. Trails should be identified and baits applied at the entry points to the structure and along the trail. Baits also may be applied in the interior where ants are trailing or emerging from wall voids. Look for specific areas around kitchen and bathroom areas where ants may be gaining access via plumbing or wiring.

Top: Pavement ant, Tetramorium caespitum. Photo: AntWeb.org. Bottom: A pavement ant “war.” Photo: Laurel Hansen.

Pavement ants (Tetramorium caespitum)
Pavement ants belong to the Family Myrmicinae, have a two-segmented node and a weak stinger. These ants may be native or a transplant from Europe. Confusion occurs based on molecular characters, but the European species is not the same as the North American species. This ant is monomorphic (one size) and polygynous (many queens). Pavement ants prefer disturbed habitats and are often found nesting under rocks, cement driveways, sidewalks, patios or concrete slabs. Ants may enter structures during colder months. Mating flights occur in mid summer and new colonies are founded by mated queens or by budding. Workers tend homopterans, especially subterranean forms and will also feed on live and dead insects. They may be attracted to sweet or greasy foods in structures during the cooler winter months and may seek shelter in wall voids. During summer months, large masses of neighboring colonies may be observed fighting to defend or enlarge foraging territories.

Management. Application of sprays directly on nesting sites along concrete areas and along trails will manage ants during the foraging season. Follow label directions. Gel or granular baits can be applied to trails and at foraging sites. Gel baits also may be applied to plumbing where there is access to wall voids during the winter months because ants will be attracted to the moisture provided in the bait.

Select Tramp (or Invader) Ants.
Any number of tramp ants have made their way into new territories around the world, particularly into urban environments. Inspections and identifications of tramp ants are being made that previously had been ignored. Several species will be introduced here with the reminder that PMPs should always be on the alert for previously “unidentified” ants.

Top: European red fire ant, Myrmica rubra. Photo: AntWeb.org. Bottom: Habitat for European red fire ant. Photo: Laurel Hansen

European Red Fire Ant (Ruby Ant) (Myrmica rubra)
This ant (Family Myrmicinae) is common in many parts of Europe and was established in Maine in the 1950s. At the present time the ant has spread throughout eastern Canada, the New England states and along the St. Lawrence Seaway as far west as Toronto. It is spreading south from Maine into northeastern states. Several years ago this ant also appeared in three locations in the far west: Seattle, Victoria and Vancouver, British Columbia.

The European red fire ant has two nodes, is red in color, measures 5 millimeters long and is an aggressive stinger. This ant prefers moist areas for nesting and foraging and does not nest within homes. When nesting in yards, they are particularly troublesome because of their aggressive nature. Typical of tramp ants, these ants are polygynous (many queens), small in size and reproduce by budding. Pest management strategies have included the use of insect growth regulators and boric acid baits.

Top: Hypoponera punctatissima; Bottom from left to right: ghost ant, Tapinoma melanocephalum; and rover ant, Brachymyrmex depilis. Photos: AntWeb.org

Hypoponera punctatissima (no common name)
This small ant is tropical but has been introduced into many areas probably via potted plants. The individual ants are also small (2 to 3 millimeters) with one enlarged node. This ant belongs to a group of ants called Ponerinae. Both workers and winged females have stingers and become problematic when the winged females are attracted to lights. The winged females sting and may cause allergic reactions. These ants have been collected throughout the Pacific Northwest, British Columbia and Eastern Canada. Management was obtained at one site by subslab application of a termiticide. At other sites application of chemicals were made at points of entry of plumbing through the slab, or by using light traps to attract the winged females. Workers occur in small numbers, are chiefly subterranean and are not a problem in structures.

Ghost ant
(Tapinoma melanocephalum)

This small ant (1.3-1.5 millimeters) has a distinctive coloration of a white gaster and legs contrasted with the black mesosoma and head that earns for the ant its ‘ghost ant’ name. It belongs to the Family Dolichoderinae and has a one-segmented flattened node.

This tropical ant has hitched rides into many locations and has been recorded in Eastern Canada, as well as Edmonton, Alberta, Seattle and Portland. In these indoor locations, the ants have been associated with potted plants, interior atriums or displays in shopping malls, or enclosures for tropical zoo animals. These ants are nuisance pests and are managed with baits.

Rover ants
(Brachymyrmex depilis)

Colonies of rover ants belong to the Family Formicinae. They are monogynous (one queen), have one node and no stinger. These small ants are a nuisance pest and are usually transported via plant material. One infestation in Portland, Ore., occurred in an office building where the ants were infesting light fixtures, electrical outlets and bathrooms. These ants also have been identified from Seattle in office buildings. Because these ants forage on honeydew, they can be managed indoors with gel baits.

Conclusion. The ants common to an area are encountered on a daily basis and are familiar to most technicians. Introduced species, particularly tramp ants, may appear in unusual settings at unusual times. Remember that pantry pests have made their entry into every area where humans store food. Many pantry pests do not fly so movement depends upon transportation of food products and other materials. The same movements occur with many other insect pests including ants. With ants it is a bit more problematic because a queen or a potential queen must be included in the transport. As people and materials are moved around the area, state, country or world, ants like pantry pests are transported and are becoming established where conditions allow.


The author is an instructor in the biology department at Spokane Falls Community College, Spokane, Wash. Email her at lhansen@giemedia.com.