[Book Excerpt] Fire Ants: A Fearsome Foe

Fire ants are active foragers and forage in trails of up to thousands of workers. These trails can usually be located without too much difficulty along sidewalks and foundations. Pulling back the grass from along the edge of sidewalks, patios, and the building foundation often reveals foraging workers and colonies which may be hidden from view.

Fire ants readily will enter structures through exterior foundation cracks, weep holes and under doorways. Mounds are often built up to and covering weep holes where the ants may then enter the building, sometimes moving all or part of the colony into the building.

Once inside a building, fire ants often forage along walls under the edge of the carpet. When these ants are found indoors, the foraging workers should be followed back to the site where the colony is located. If the ants are entering and exiting from under the wall, the outside should be inspected along the foundation to see if the ants are coming from a colony located outdoors. Often, a fire ant mound is located against the structure, and the ants are entering through an exterior crack.

The author has encountered a number of situations where fire ants were nesting in the gravel and debris on the flat roof of a commercial building.

Mulch in landscape beds are a common site for fire ant colonies. To avoid being stung, a small hand rake should be used when inspecting mulch for fire ant colonies. Mounds are often found at the base of trees and shrubs and in the crotches of trees.

Any item in contact with the soil, such as logs, stones, firewood and other debris, could harbor a fire ant colony. Mounds of displaced soil are often present running along cracks on top of sidewalks and patios. Sprinkler heads and water and gas meter boxes are a common site to find colonies. Colonies in meter boxes often follow the pipes into the structure, usually to the space beneath the bathtub (bathtrap). It is not uncommon to find large fire ant mounds inside a bathtrap.

If subslab heat ducts are present, an inspection mirror and flashlight can be used to inspect back into the ducts. Piles of soil inside the duct might indicate a fire ant colony. Foraging ants may also sometimes be seen in the register wells of the duct system.

CONTRIBUTING CONDITIONS. As with most ants, moisture is a limiting factor in the survival of fire ants. However, fire ants thrive in such a wide variety of habitats that it is nearly impossible to impact an infestation of these ants by attempting to limit moisture conditions. If conditions exist which result in excess moisture (e.g., poor foundation drainage or water leaks), they should be corrected.

As many exterior cracks as possible should be sealed. Firewood should be stored off the ground and as far from the structure as possible.

MANAGING INFESTATIONS. In areas where fire ants are common, it can be impossible to totally eliminate them at a particular property. Constant reinfestation of treated properties from adjoining yards is a continual reality.

The three basic approaches for controlling fire ants are one or all of the following: (1) mound-to-mound treatment; (2) broadcast bait treatment or broadcast granular treatment; and (3) perimeter treatment.

Protecting some properties may involve a combination of these three methods. Large properties, however, may be feasibly treated primarily by broadcast baiting due to the expense of applying mound-to-mound techniques. Any mounds next to buildings on large properties can be treated by a mound-to-mound treatment technique followed by a perimeter treatment and/or baiting around the building.

Researchers at Texas A&M University recommend a two-step process for controlling fire ants. First, a broadcast fire ant bait is applied and allowed to sit for about two days thus permitting foraging workers to feed upon the bait, carry it into the nest and distribute it through the colony. Mound-to-mound treatments with conventional residual treatments as described below are then used to eliminate visible mounds.

Mound-to-Mound Treatment. Several methods may be used for treating individual fire ant mounds that will kill the mound within a few hours to a few weeks, depending on the product used. A major disadvantage with using water-based residual drenches or mound injection is their labor-intensiveness because each mound must be located and individually treated. Additionally, such applications may result in "satelliting," where surviving ants relocate to nearby sites and establish one or more new colonies. Smaller mounds are often overlooked and serve as reinfestation sources. Ants from adjacent properties often quickly reinvade treated properties.

Mound Drench. The mound is flooded with a large volume of an appropriately labeled, water-based insecticide. More than one gallon is needed for most mounds and larger mounds may require several gallons. Drenches are most efficiently applied with a low-pressure power treating unit mounted on a truck. A disadvantage of this technique may be the failure to reach all areas of the mound to kill the queen or queens inside. Using too little volume may permit the survival of one or more queens and results in satelliting.

Mound Injection. A few aerosol and water-based insecticides are labeled for direct injection into fire ant mounds. This technique is typically more effective at penetrating throughout the mound than mound drenching.

Baits. Baits labeled for fire ants may be used for individual mound treatment. A small amount of bait, usually a tablespoon or less, is applied onto and up to 3 feet around a mound. The great disadvantage of using baits to treat mounds is the length of time it may take for results to occur. New fire ant baits, however, can kill mounds within as quickly as 24 hours and are less labor intensive than mound drenching.

Powders or Dusts. A few dry, dust or powder products may be labeled for direct application to fire ant mounds.

Broadcast Bait Treatment. Fire ant baits may be applied to large areas (e.g., lawns) using various types of spreading equipment. Baits are found by foraging fire ants and carried into the mound to be fed to other workers, larvae and the queen(s). The advantages of broadcast baits is their ease of application to large areas, control of unseen and small mounds, and control of some of the colonies located on neighboring properties. Complete control is often not achieved, however, due to: (1) ants from some mounds avoid the bait; (2) the bait fails to drop close enough to some colonies to be discovered by foragers; (3) the baits are sensitive to sunlight and moisture and break down quickly; and (4) the baits are not specific to the fire ant, and competing ant species may remove the bait.

Broadcast bait treatments are most effective when combined with mound-to-mound treatments. The amount of bait actually applied is quite small (1 to 1½ lb. per acre or less than ½ ounce per 1,000 ft2) and requires a spreader capable of low-volume application of dry materials.

A University of Florida publication, "Imported Fire Ants and Their Management in Florida," recommends the following when using baits for fire ants: (1) "use fresh bait;" (2) "apply baits when the grass and ground are dry or drying and rain is not expected, preferably for the next 24 hours;" and (3) "apply baits in late afternoon or evening" because fire ants will forage at night during the summer.

Perimeter Treatment. The application of a water-based residual product to the foundation and landscaping around a building where fire ants are present on the property can be beneficial in limiting indoor foraging by fire ants. Perimeter treatments may be applied whenever ants are found near or next to the building. Mounds living in landscape mulch may need to be exposed by raking back the mulch and drenching each mound thoroughly.

Treating Fire Ant Colonies Inside a Building. Many, if not most, fire ant trails inside a building originate from a colony located outside. Ant mounds inside a wall void require treatment with an aerosol or water-based formulation (beware of electrical outlets in walls) to penetrate through the soil. Mounds inside a bathtrap may be treated by mound injection or by mound drenching. A colony living in soil carried into a structure may be treated by drenching and then the soil removed and deposited outside.

It is also recommended treating foraging fire ant workers indoors after the colonies have been treated. Left untreated, these workers could still contact people and sting them. Foraging trails under carpeting can be treated by injecting a residual dust under the edge of carpets.

Fire Ants Inside Air Conditioning Units and Other Electrical Appliances. This ant may be attracted to electric contact points inside air conditioners, traffic light control boxes and similar electric appliances found outside. Mounds are often constructed next to and up inside the metal cases surrounding these devices. Mounds outside boxes can be treated by mound drenching, mound injection, or a surface dust or granular application to kill the mound immediately. Mounds inside boxes may need to be handled by authorized persons who can open the boxes. A wet/dry vac may be used to remove soil and ants and these taken away from the box to be treated. Spot applications to the surfaces inside the metal case may help prevent foraging workers from reaching the contact points and causing a shutdown of the unit. Where possible, sealing of the cracks around the case and periodic perimeter treatments around the unit can help exclude ants. Area wide efforts, as described above, may be beneficial in reducing the presence of fire ants on the property.

The author is technical director of Terminix International, Memphis, Tenn. Contact him via e-mail at shedges@giemedia.com.