Successful ant management assumes two directives: “Find the nest” and “Locate the trails.” These are preceded by the correct identification of the pest ant involved. The nest location and the trails are dependent on one another as well as the chemical: bait, spray or dust that is employed. Trails will lead to the discovery of nests and chemicals applied with trail information all can be applied to management. Ants trail for a number of reasons and knowledge of the biology of the species involved will help determine the method of attack.

The first directive for proper ant management is “Find the nest!” This task remains of primary importance, but with the development of effective baits and chemicals that have “transfer” capabilities, the emphasis has shifted to “Follow the trail.” Inspection for trails of ants is the most time-consuming factor in ant management.

Understanding the social behavior and habits of different ant species is important to understanding management. Ant trails are common with most ant species and this trait is vital to understanding ant management. The three most common ants that are pest species according to national surveys are carpenter ants, odorous house ants and pavement ants. Other ant species in specific areas include the Argentine ants in the West and South and the velvety tree ants in the Western United States and Canada.

All ants are social with a division of labor including the mated queen, workers and brood consisting of eggs, larvae and pupae. Mature colonies also will contain the reproductives, winged males and females who, depending on the species, may leave the colony to mate and establish new colonies. Ants work together in nest building; in providing care for the brood, queen and reproductives; in moving nest sites; and in foraging for the colony. Not all ants in a colony will leave the nest to forage at the same time. Estimates are that 10 percent or fewer of ants are foragers at any one time. The non-foraging ants are involved in activities within the colony where their various roles will vary depending on age and requirements of the colony. The oldest of the workers will forage for the colony supplying nutrients for non-foraging workers, brood, queen and reproductives.

TRAIL BEHAVIOR. Ants move together in a trail for the purpose of establishing a new colony, moving from a parent to satellite nest(s) or sub-nest(s). Nest building varies among ant species from simple collection of brood under a pile of leaves to extravagant parent and satellite nests to a constant rearrangement of sub-nests as foraging arenas are changed. Carpenter ants maintain a parent nest, often outside a structure, while satellite nests are established in subfloors, attics or voids within a structure. Ants maintain communication between these nests by trails. Odorous house ants, Argentine ants, pavement ants and velvety tree ants may move sub-nest(s) with a queen(s) to different foraging arenas or into structures often from an exterior nesting site.

The most common type of trailing behavior occurs in foraging activity and may be observed with most ant species. Most colonies require both carbohydrate and protein at various times during the life cycle. Carbohydrates are often supplied in nature by homopterans (aphids, scales) producing honeydew or from nectar from flowers. As homopterans live in trees, shrubs and other vegetation around a structure, the foraging trails of ants will lead from nesting sites to these foraging arenas. Ants also may be attracted to a carbohydrate source within a structure, such as candy, fruit or other sweets. Protein required by colonies is usually met by foraging on insects or in structures by feeding on pet food.

Trails by ants are fluid; that is, different ant species forage at different times of the day, at different temperatures and on different substrates. A black utility wire that leads from the structure to trees makes a good trail from a satellite nest to the foraging arena, especially if the wire avoids direct sunlight and is therefore cooler than a wire exposed to direct sunlight and may have too high a temperature to navigate during the heat of the day. Timing of inspections is critical as ants change trails in response to these factors.

Ants commonly follow structural guidelines that facilitate movement between two points. Structural guidelines may be a fence; a wire; an irrigation pipe or hose; the edge of a concrete structure such as a patio, sidewalk, steps or driveway; or even the edge of a garbage can. Again, direct sunlight and temperature will alter these guidelines and may be camouflaged by lawn, shaded areas, trees or other vegetation. Technicians need to inspect these areas to determine trailing activity and remember that environmental conditions will change trails.

Trails may be marked by trail pheromones. As each ant passes along the trail, more trail pheromone is released from the tip of the abdomen. Pheromones may be produced in the hindgut or Dufour’s gland in carpenter ants while pheromones are produced in abdominal sternal glands in odorous house ants. Pavement ant pheromone is produced from the poison gland. The release of pheromones keeps the trail strong and allows other members of the colony to determine the quality of the trail and direction of the food source. Pheromones usually are volatile and need the constant reinforcement of other foragers.

Ants are recruited by pheromones or by tandem running with other ants. Tandem calling followed by tandem running is employed by some ants where the “calling” or recruiting occurs with the release of a chemical, often from the poison gland, followed by the worker ants following the leader releasing the pheromone. Pavement ants may be recruited in this manner.

Ants commonly follow structural guidelines that facilitate movement between two points. Direct sunlight and temperature will alter these guidelines.
L. Hansen
Ants commonly follow structural guidelines that facilitate movement between two points. Direct sunlight and temperature will alter these guidelines and may be camouflaged by lawn, shaded areas, trees, or other vegetation.
L. Hansen
Ants commonly follow structural guidelines, including the edge of a garbage can.
L. Hansen

When a particularly strong foraging arena is employed by a colony, a trail may be physically constructed through lawn or other vegetation to provide a more direct route to the arena. This is commonly witnessed with carpenter ants where vegetation, small rocks and debris are removed from the trail. Some of these trails may be 4-5 cm in width. Trails also may become subterranean and ants will excavate passageways beneath the soil surface from a nesting site to a foraging arena. This has been observed with nests in partially buried railroad ties or landscaping timbers with trails constructed underground. The trail leading away from the buried wood is lined with wood excavated from the nest site and emerges near the base of a fir tree. Ants also may follow roots of trees in underground trails. As these trails are hidden, inspection should include the bases of nearby trees or shrubs to determine if ants are emerging near the tree and establishing their foraging arena in the trees.

Other foraging arenas that are more temporary may induce ants to move sub-nests to different arenas as the food sources are depleted and as the numbers of brood increase. Odorous house ants or velvety tree ants that are both multi-queened often will set up temporary nests or sub nests and structures may be invaded within a day or two as new foraging arenas are located.

INSPECTION TIPS. Trail inspections become an important tool in management protocols. Homeowners may be of assistance but technicians should recognize the importance of inspecting possible trailing activity at specific times of day. Guidelines such as fences, wiring and plumbing leading to the structure, plus any vegetation in the form of trees, shrubs and plants that are in contact with the roof or siding, must be inspected. If foraging arenas are located in trees, ants may be visible on the trunks. These ants may be traced back through the vegetation to entry points on the structure.

Trails also occur within structures with ants following various structural guidelines, such as along door and window frames, the edges of carpets (tacking strips under the edge of carpeting) and counter edges. Ants prefer to establish trails on dark surfaces and along edges (structural guidelines). Within wall voids or other structural spaces, ants will trail on plumbing and wiring. Dust applications are ideal to reach some of these areas by injecting small amounts of a dust formulation (using plastic nozzles) on the side of electrical boxes after removing covering plates. Dusts also may be injected into accessible openings around pipes and plumbing fixtures.

The number of ants on trails will vary by species, size of the colony and time of day. Carpenter ants have an increase of ants emerging on trails at sunset and a decline at sunrise and during the daylight hours. Some trails of carpenter ants will have ants, sometimes several abreast, or at other times of the day, the ants will be spaced several feet apart along the trail. Odorous house ants and velvety tree ants are very numerous on the trails, especially when the ants are entering or exiting a structure. Close inspection of the foundation will often reveal these trails.

A wire leading from the structure to trees makes a good trail from a satellite nest to the foraging arena, especially if the wire avoids direct sunlight.
L. Hansen

Once trails have been located, management of infestations can be facilitated by removal of the trail features (vegetation, guidelines, etc.) or with the use of chemical sprays and/or baits. Placement of a chemical spray, preferably a chemical that has demonstrated transferability, should be placed on trails, under the lower edge of the structural siding, at structural entry points and along any guidelines where ants are trailing. Ants exposed to slow-acting sprays will transfer the material to other ants in the nest(s) and eliminate the colony.

Locating trails is imperative for bait placement. Slow-acting baits are effective but lack the ability to recruit unless baits are placed within a few centimeters of the trail, especially when ants are foraging to an established arena. Ants will not find baits placed at random locations; therefore, the more efficient use of the material is to place the bait where it will be discovered by the ants. Once the bait is encountered, other ants will be recruited.

Proper location and chemical placement along trails will result in successful ant management because ants follow trails to the nest(s). When trails are located and treated, callbacks will be reduced; however, treatments require a thorough inspection and knowledge of ant behavior.

The author is an instructor in the biology department at Spokane Falls Community College, Spokane, Wash.