Pavement Ant Control

Any large commercial building presents a daunting task when attempting to keep it as free from pest activity as possible. Large buildings are complex, with miles of electric wires and pipes, hundreds of cracks, and thousands of voids. Although every floor may be designed the same, as in a large hotel, each will be different in a pest control sense because each floor has its own idiosyncrasies its own sanitation issues and its own level of maintenance and structural integrity. Different types of pests utilize these factors differently, and will be found living in different areas of buildings due to the individual requirements of each. Pavement ants are no exception.

Pavement ants have a preference for living next to and under solid items such as slabs, driveways, patios, stones, and landscape timbers. They are soil dwellers that generally live in close contact to soil, or that will carry soil up into a void they choose as home. These facts make pavement ants more likely to be a problem in the lower levels of a building, particularly the ground floor or subfloors. The presence of soil-containing atriums also compound pavement ant infestations. This article will briefly review the biology and habits of the pavement ant and discuss procedures for dealing with this ant in large commercial buildings.

PAVEMENT ANT BIOLOGY. The pavement ant is a small, dark brown ant about ¹/₈ inch in length, with the workers all being about the same size. It has two segments, or nodes, between its thorax and abdomen, and it has a pair of spines on its thorax. This ant is distinguished from similar appearing ants by the lines or grooves on its head and thorax. A mature colony hasnumerous queens and as many as 30,000 workers.

As stated earlier, the pavement ant likes slabs and concrete. A colony will displace a good deal of soil as it constructs its underground galleries. This soil has to go somewhere, so it ends up in a nice mound on the surface of the ground or next to a patio or sidewalk. If the colony is located under a sidewalk or a slab foundation, the ants carry soil up through cracks, and piles of soil appear and grow larger day by day. This is usually the first sign that a colony is present, and is a major clue when inspecting for pavement ants.

Pavement ants feed on a wide range of foods, and are partial to honeydew produced by aphids and mealybugs. This ant is the one that is often seen swarming over any bit of food spilled on a sidewalk or a floor. This ant establishes solid trails of workers to and from food sources, and they are most active at night. Trails can be found during the daytime, although finding them takes a bit more effort. Outside, daytime trails will usually be hidden along the side of the foundation or a sidewalk underneath grass or other vegetation lying against it. Inside, the trails will be found under the edges of carpets along the tack strip.

Electric wires and water pipes in walls provide pavement ants "highways" from one room to another and to other floors. Water and drain lines also provide a ready source of moisture from condensation on the pipes.

Mature colonies produce winged swarmers in the spring, although these can sometimes appear at other times of the year inside heated buildings, especially during the fall. In fact, swarmers can cause greater problems than the worker ants in large commercial buildings. The workers may prefer to stay on the ground level and may be rarely seen inside large buildings. The swarmers, however, climb up through walls and enter false ceilings one, two, and even more floors above the ground floor. Swarmers are then attracted to the lights in the ceilings, and many end up in the living space of the rooms below.

The most frustrating thing about pavement ant swarmers is that they can be quite sporadic. A couple of small swarms may occur over a period of a few days followed by a large swarm, or vice versa. New swarms large and small can continue to occur for several weeks depending on environmental conditions. No one can predict exactly when and for how long pavement ants will swarm inside a given building. Stopping these swarms is often the most difficult task in dealing with pavement ants in large buildings.

Another critical factor compounding pavement ant swarms is that they swarm at the same time of year as subterranean termites, and pavement ant swarmers are about the same size and color as termite swarmers, although maybe a little larger. An experienced person can easily distinguish between the two. Employees in commercial buildings, on the other hand, don't have the expertise, and so can become upset at the occurrence of a termite swarm soon after efforts to control pavement ant swarms has been completed.

FACTORS AFFECTING CONTROL. Obviously, the key to solving a pavement ant infestation in any building involves finding and killing the colony. In homes, accomplishing this task is usually quite easy. In a large commercial structure, however, this can be a difficult task, particularly when the offending invaders are the winged swarmers. In this latter situation, swarmers often appear without any worker ants having been found. Finding the workers following a swarm can sometimes be difficult, and the workers can be a key to solving many situations involving swarmers.

• Finding the colony. The first step in any infestation involving ants is to find a specimen to identify. Once the infesting ants have been confirmed as pavement ants, an inspection is necessary to attempt to pinpoint the location of the colony or colonies infesting the building.

The inspection should begin on the ground floor and/or subfloors of the building. Even if pavement ant workers are found on upper floors, they usually are traveling there from colonies located at ground level. This fact holds true in most infestations. Once live workers are found, an attempt must be made to follow the trail back to its origination point. This point might be under a wall, through a crack in the foundation, or even through a window frame.

If the ant trail is originating from under a wall, is the wall an exterior or interior wall? If the trail ends at an exterior wall, the colony involved will often be living outside or inside that wall. In most cases involving interior walls, the trail picks up on the opposite side of the wall and will need to be traced further.

If live ants cannot be located, use needle- nose pliers to lift up the edge of the carpet near areas where ants have been seen. Pavement ants are notorious for trailing along the bases of walls under the carpet. Since they are most active at night, under carpets is usually where pavement ants will be found during the daytime. Avoid pulling the carpet up too much, as it could be hard to replace it properly. Pull the carpet up enough to see if ants are trailing underneath, and then move down several feet and repeat the process. Ant trails can be quickly followed through several rooms, if necessary, using this technique.

Occasionally, a pavement ant trail will disappear under the carpet toward the center of the room away from the walls. In this situation, a crack in the slab floor may be where the ants are entering. To check this, the carpet needs to be pulled back enough to expose where the ants are going. Be sure to get the customer's permission, and inform them that a professional carpet layer might be needed to lay the carpet back properly.

In buildings with floating slabs, the exterior walls where expansion joints are located are a common source of pavement ant infestations. In any situation involving expansion joints or stress cracks in slab floors, the exact location of the ant colony underneath the slab will usually be indicated by displaced soil on top of the slab.

Displaced soil is one of the most readily apparent indicators of pavement ant activity. Piles of soil can sometimes be found on top of carpets or floors. Outside, displaced soil quickly pinpoints an ant colony, and further investigation is necessary to determine whether the displaced soil is the result of pavement ant activity.

In large buildings, exterior colonies of pavement ants are almost always involved in the infestation. One of the most common reasons for failure in controlling pavement ants (and other ant species) is overlooking the exterior of the building as part of the source of the infestation, or as the reason the building is quickly reinfested. Displaced soil may not always be present, although it usually is. Use a shovel or a small hand rake and move soil and mulch next to foundations to determine whether ant colonies are present. Pavement ant colonies will generally be within the top few inches of soil. It is also important to turn over stones, landscape timbers, and other items to check for colonies.

Another important spot to check for a pavement ant colony is inside water meter boxes. Pavement ants sometimes will set up shop in these areas and follow water lines under the ground back into the building.

TREATING FOR PAVEMENT ANTS. Once a pavement ant colony is found, treatment is generally not difficult. Outside, colonies can be drenched with a few ounces of a properly labeled insecticide. In cases where numerous colonies are involved in landscape mulch or under stones or landscape timbers, the colonies will have to be ex posed in order to treat them. Treating over the top of the mulch or items will fail to reach and kill most of the ants.

In one case involving a multi-story office building, the ant infestation was originating from about 50 colonies or subcolonies located under stones used as a vegetation-free barrier around the building. Repeated perimeter treatments failed to eliminate the ant sightings inside the building. By looking for displaced soil, the ant colonies were quickly pinpointed. Each rock under which a colony was living was turned over to expose the ants, and then the colony was drenched. Although this proved to be a little more time-consuming than simply applying a perimeter treat ment, in the long run it took far less time than returning to apply three or four perimeter treatments. Exposing the colonies to treat them stopped the infestation in this case.

If a pavement ant colony is found to be living inside a wall, the wall can be drilled and treated with an appropriately labeled residual aerosol insecticide. Conquer insecticide applied using an aerosol generating machine, such as the Actisol or Micro-Injector, will also control colonies inside walls. The reason that an aerosol formulation is needed is that the ants will usually bring soil up into the wall void. The aerosol can effectively penetrate this soil.

If the ants are found trailing out of a crack in the floor of the slab, three approaches can be attempted.

(1) Apply a residual insecticide into the crack using a crack and crevice tip on a compressed air sprayer. Try to apply as much insecticide as possible down into the crack. This technique is most useful in stopping swarmers from coming out of the crack, and is rarely successful in controlling an entire colony. When swarmers are involved, it is also advisable to caulk the crack if possible.

(2) Baits can be placed in the path of all ant trails both close to and away from where they are entering the crack. Follow-up on a daily or every-other-day basis is necessary to be sure the ants are feeding on the bait. If not, switch baits until one is found that that particular colony likes. Baits can take a number of days to be successful, so the customer will need to be advised of this fact and be prepared to be patient.

(3) The most effective, although time-consuming, method for dealing with subslab ant colonies is to drill through the slab and treat the soil underneath, similar to the treatment done for termites. Dragnet FT termiticide is labeled for this type of application for ants. It is important to be sure that the colony is definitely located under the area being treated. Otherwise, the treatment will be for naught. Treatment under slabs is necessary only where the ants are found, so the entire building will not need such treatment.

If the inspection is unsuccessful in finding the location of the infested colony or colonies, one or both of the following can be attempted.

• Bait can be placed in the path of all known ant trails. Frequent follow-up visits are needed to ensure ants are feeding on the bait.

• Perform an inspection at night at about 10 or 11 p.m. Since pavement ants are most active at night, it is more likely that trails can be found that will lead back to the colony. Once found, the colonies can be treated as described previously.

DEALING WITH SWARMERS. When swarmer ants are entering rooms, an attempt should be made to determine their entry points. If the ants are entering from above the false ceiling, look for holes in walls above the ceiling through which the ants could be entering. Walls bordering the building's exterior are the ones most often involved.

If the ants are determined to be crawling up wall voids to exit from cracks around windows, in walls, or above false ceilings, the best approach is to drill the likely wall voids and treat them with a residual insecticide. Drill at the base of the wall and apply Drione or Ficam dust insecticide if the void is hollow, or use a residual aerosol insecticide if the wall contains insulation.

If swarmers are exiting through a crack in the floor, apply a residual water-based or aerosol insecticide into the crack, and then caulk it shut. Even if the crack is treated, swarmers can still crawl out and die where they can be seen. Caulking prevents this from occurring.

Placing an insect light trap above a false ceiling is helpful in many cases to prevent the swarmers from entering the rooms below where they can be seen by the building's occupants.

It is always important to try and find the colony's location when swarming occurs. Treating the colony itself probably will not kill the swarmers because they are most likely already above ground waiting to swarm. Finding and treating colonies, however, stops swarming activity in future months or years. Also, feeding baits to worker ants will not stop swarming because the swarmers usually have stopped feeding by the time swarming is to occur.

Controlling pavement ant infestations in large buildings takes patience and persistence. In most cases, several trips will be necessary because new activity can pop up in other areas of the building. A series of regular services should be scheduled to deal with these occurrences. PCT

Stoy Hedges is manager of technical services for Terminix International, Memphis, Tenn. He authored the PCT Field Guide For The Management Of Structure-Infesting Ants and the PCT Field Guide For The Management Of Structure Infesting Flies. He also co-authored the PCT Field Guide For The Management Of Urban Spiders with Dr. Mark Lacey of Paragon Professional Products.