Imported Fire Ants in Lawns, Turf, and Structures

ANR-0175, Revised May 2003. Kathy Flanders, Extension Entomologist, Associate Professor, Entomology and Plant Pathology, Auburn University. Originally prepared by Patricia Cobb, former Extension Entomologist, Professor Emerita, Auburn University, and Faith Oi, former Extension Specialist.

Red imported fire ants were accidentally introduced from South America into the United States at the port of Mobile in the 1930s. By the mid-1970s, they had spread into much of the southeastern United States. Presently, fire ants are reported in all of Alabama's sixty-seven counties. It now infests parts of California and potentially can infest other parts of the United States. Efforts to prevent the spread of fire ants continue to be important to nurserymen, sod producers, and homeowners throughout the region.

Fire ants range in size from small to large.

Red Imported Fire Ants

Although fire ant mounds may interfere with mowers and other turf-maintenance equipment, the real problem is the painful stings that fire ant workers can inflict. In addition to being associated with lawns and turfs, fire ants have now been reported as indoor pests. Established colonies have been found in structures and inside equipment casings.

If it were not for the painful experiences associated with fire ants, almost anyone would find them fascinating. Their life cycle and social behavior are surprisingly complex.

The Mound

Although not essential, the fire ant mound is usually the most obvious part of the colony. The height of the mound and the depth to which the core extends into the soil are determined by factors such as colony size and age and soil texture and moisture. Inside the mound is a teeming metropolis of worker ants"all sterile females capable of stinging.

Radiating out from the mound are underground tunnels that open to the surface several inches to several feet away. These are passages that worker ants use to leave and return to the colony. Workers forage for food on the surface and bring it back to be processed. Last-stage larval forms "digest solid food, which then becomes available to other ants in the colony. Only these developing larvae can process solid food; other stages must feed on liquids.

Inside a fire ant mound.

Life Cycle

Fire ant workers (sterile females) range in size from small to medium to large. Workers are produced by queen ants that are little more than egg-laying machines. A typical queen may lay more than a thousand eggs a day and may live for 5 to 7 years or more unless food is limited. Most colonies have only one queen. However, colonies with more than one queen (multi-queen colonies) have been found in Alabama.

Eggs hatch in about a week into legless larvae that go through several growth stages. After 6 to 12 days as larvae, developing fire ants enter a transitional pupal stage that lasts for 9 to 16 days. The white or clear forms that are found in fire ant colonies are developing immature stages. These stages are moved by workers up or down in the mound, depending on the external temperature and moisture conditions.

Fire ants (as well as other insects) are exothermic, or "cold-blooded, animals. This means that they cannot maintain their body temperatures by internal mechanisms the way warm-blooded animals can. Their body temperatures and functions depend on the outside temperature.

A fire ant worker lives an average of 1 to 6 months, depending on its size. Larger workers live longer than smaller ones. Unmated winged males and females may be found in colonies during warmer months.

Fire ant winged reproductive females and males fly and mate, and new colonies are established during warmer months. Males die soon after mating. Mated queens lose their wings after landing on the ground; many are eaten by predators such as spiders, lizards, other ants, and ground beetles. Those queens that survive dig chambers into which a few eggs are laid. These first eggs hatch and mature into workers that care for the queen and the next broods of workers. Visible mounds appear above the turf surface as the colony increases in size, usually within several weeks or months.

Controlling Fire Ants Outdoors

Several control options are available for infested non-crop areas. Control strategies may depend on such factors as the size of the site, its uses, how frequently and by how many people it is used, and the availability and expense of labor, as well as personal preferences.

Generally, fire ant mounds can be eliminated on a site at any given time; the problem is that reinfestation from surrounding, unmanaged areas cannot be prevented. In fact, once fire ants and other predatory insects, including other ants, are eliminated from a site, reinfestation can occur without competition. Therefore, controlling fire ants on a site usually involves an ongoing effort. In addition, the degree of infestation and management of surrounding areas usually influences the speed at which managed sites are reinfested.

Fire ants build large mounds that can make lawn care difficult.

Anything that disturbs the colony usually causes the fire ants to relocate. For example, frequent mowing may cause mounds to relocate along borders or unmowed areas. Fire ant treatments can also cause colonies to relocate. If any workers survive, they will often attempt to relocate the queen to a new site.

Some fire ant control materials are designed to be used as mound treatments. Others are meant to be broadcast. A third group can be used either as a mound treatment or as a broadcast treatment. Fire ant control products vary greatly in cost as well as in the length of time they control fire ants. Fire ant control materials have two names. The common name identifies the actual control material. The trade name is the brand name. Common names are used here. A companion Extension publication ANR-175-A, "2004 Fire Ant Control Materials for Alabama Homeowners," lists trade names and is updated annually. Materials listed on this sheet are those that are readily available to Alabama homeowners at home improvement stores, garden centers, and farmers cooperatives.

Mound treatments alone are commonly done on turf sites of an acre or less, including lawns. Treatments on, in, or around mounds are done as infestation occurs and mounds appear. A disadvantage of mound treatments is that the colony will probably just move if the queen is not killed. It may be necessary, therefore, to treat the colony again.

Broadcast treatments involve applying an insecticide over an area. One advantage of broadcast treatments is that new, "young colonies may be controlled before mounds appear above the turf. Therefore, the need for continual treatment of visible mounds may be reduced until reinfestations occur. A disadvantage of broadcast treatments over larger areas is that often fire ant predators may be eliminated so reinfestations can occur without competition. Read the label to make sure a particular chemical is registered for your site.

Broadcast Bait Treatments

Baits should not be confused with granular insecticides, although baits are formulated as particles that are measured and applied similarly. Baits generally work slower than other formulations. Baits become part of the fire ant food chain and, therefore, are usually passed to the queen.

The way baits work to eliminate colonies is usually not the same as the poisoning effects of other insecticides. Hydramethylnon, spinosad, and fipronil baits are slow-acting insecticides. Abamectin, fenoxycarb, pyriproxifen, and S-methoprene baits disrupt the queen,s reproductive potential but don,t kill adult fire ant workers. Baits that disrupt the queen,s reproductive potential do not usually eliminate worker ants quickly so colonies die over a period of several weeks. This may be an advantage because the continued presence of worker ants may discourage reinfestation. colonies treated with fipronil, hydramethylnon, or spinosad bait usually die in 2 to 4 weeks. These baits typically give 3 to 9 months of control. Abamectin, pyriproxifen, S-methoprene, or fenoxycarb baits take longer (usually 6 to 8 weeks), but the duration of control is higher, usually 6 to 12 months. The two types of baits can be mixed at half the labeled rate of each. For example, mix hydramethylnon with methoprene. The bait mixes usually act in 2 to 4 weeks, yet give 6 to 12 months of control.

When temperatures are in the 70s and 80s, applications of baits are most effective because ants are usually foraging at that time. If drought or other environmental stress conditions exist and fire ants are not actively foraging, delay bait applications. For example, if it is extremely hot, apply baits early or late in the day when temperatures are lower. Ants will also forage at night.

For more information on using fire ant baits, see Extension publication ANR-1161, "Getting the Most Out of Your Fire Ant Bait."

Other Broadcast Materials

The available selection of insecticides for fire ant control has changed dramatically since the removal of chlorpyrifos for use by homeowners and the phaseout of diazinon in 2004. With one exception, the broadcast insecticides are fast acting. They kill a wide variety of insects on contact. Most of the broadcast insecticides are granular formulations. The residual control of a particular brand will depend on how long the active ingredient persists in the environment. Fast-acting insecticides kill foraging fire ant workers but are not designed to be carried back to the nest and the queen. The label on the product may indicate how long a particular brand may last in the environment.

Fipronil granules act slowly to eliminate a fire ant colony, including the queen. It takes about 4 weeks to control fire ant colonies. This material usually gives about a year,s worth of fire ant control. The effectiveness of this material is related to how well it is applied. It must be evenly broadcast over the entire area at the proper rate.

Insecticide mound treatments include dust, granular, bait, drench, and injection. Always apply insecticides according to label directions. In the case of fire ant mound treatments, most product labels state specifically where"on and/or around the mound"the dosage should be placed. Never apply more than the labeled dosage. In addition to being costly and illegal, over-application may simply encourage the colony to relocate a few feet away from the original mound.

Dust treatment of mounds should be done in the middle to late afternoon. Apply when the soil is not excessively wet or dry, when rain is not expected, and when irrigation can be delayed for 24 hours. Several dust treatments are available.

Granular formulations are applied by sprinkling a measured amount of insecticide granules on and/or around the mound. Apply water after applying the granules if required by the label.

The fire ant baits listed above can also be used as mound treatments. As noted above, they act more slowly than other mound treatments.

Drench applications are registered for certain formulations of insecticides. Instructions on the labels of these and other insecticides registered for mound-drench applications require mixing the insecticide concentrate in water and pouring the mixture into and around the mound.

Mound injections are done with aerosol containers provided with injection rods. The rod is inserted into the mound and the toxicant released. Although these systems are more expensive, this method is a fast-acting mound treatment, and the potential for exposure to and runoff of surface residues is reduced. Be careful to avoid contact with ants that may sting.

Nonchemical remedies. Noninsecticidal controls have been proposed as a part of the ongoing effort to suppress fire ants. Anything that disturbs the colony may cause mound relocation.

Boiling water (2 to 3 gallons per mound) has been shown to control fire ant mounds.

Mixing the contents of two mounds may cause relocation or removal of queens and brood.

Cereals, such as rice, grits, or meal, are sometimes thought to aid in fire ant control when sprinkled on the mound. However, there is no research to indicate that these materials have any effect. Remember"worker ants cannot feed on solids.

Gasoline and related materials are not registered for control of fire ants. Moreover, they are dangerous to handle; they are usually expensive; and they kill grass and other plants that are contacted.

Management Strategies for Controlling Fire Ants Outdoors

For large lawns, a two-step method may give the most satisfactory, cost-effective control. In this management strategy, a broadcast bait is applied, and then a mound treatment is used to eliminate the workers in the few, most troublesome colonies. The other colonies will eventually die out from the bait treatment.

Management of fire ants on large non-crop areas such as athletic fields, golf courses, camping sites, and parks may involve spot bait treatments followed by treatment of individual mounds. An effective program for controlling fire ants in large frequently used areas involves making spot applications of a bait, waiting 3 to 5 days (giving worker ants a chance to bring bait particles into the colony), and then treating the most visible, intrusive mounds with a quick-acting insecticide. In areas where use is not frequent, or to control sources of reinfestation in border areas, spot, perimeter bait treatments alone may be more practical. This leaves some fire ants to prey on new queens that fly into the area.

Sod producers and nurserymen have special regulations for treating sod and nursery plants that are to be shipped out of the fire ant quarantine areas. Contact the Alabama Department of Agriculture and Industries, Plant Protection Division, Beard Building, Montgomery, Alabama 36109, for more information on these regulations.

Biological Control

Decapitating flies (phorid flies) are being evaluated for effectiveness in controlling fire ants. See Extension publication ANR-1149, "Biological Control of Imported Fire Ants," for more information. These organisms are not available for purchase by individuals. They are being established at carefully controlled sites from which they will spread naturally into surrounding areas.

Controlling Fire Ants Indoors

Over the years, fire ant workers have become more common indoors. Generally, fire ants come into buildings searching for food, especially meats or greasy food. If fire ants are found indoors, remove children and pets from the immediate area. Try to follow the ants, trail to determine what they are eating and where they are coming in. Ants holding food are usually on a path back to the nest.

A common place for fire ants to forage is the kitchen, but do not overlook trash cans, diaper pails, or food that may be in other areas of the building. Once the ants, food source has been found, remove it or seal it in a tight container.

When inspecting for the ants, entry point, first check around doors, windows, and places where pipes, ducts, and wires enter the house. Be mindful that fire ants can enter a structure from almost any location.

After determining where the ants are entering, spray the ants and their trail with an insecticide. Any insecticide spray registered for inside ant control should be effective. Many sprays are available. A nonchemical alternative would be to vacuum the ants and immediately dispose of the dust bag outside.

Follow all instructions on the product,s label. Be careful not to spray around food or eating utensils or into areas where wires are present. Baiting indoors with a bait station may be effective, but it could prolong the time the fire ants are in the building. When the ants are killed, seal their entry point with appropriate caulking, weather stripping, or screening.

Once the ants are controlled in the building, inspect outdoors for their nesting sites, starting close to the spot where you found the ants entering. Work your way around the building,s perimeter, including crawl spaces. Pay particular attention to areas around utility boxes and heating and air conditioning units. If mounds are not found against or near the building, work your way out away from the building until you find mounds. Treat the mounds with any of the insecticides listed for outside use. Consider using one of the faster-acting control methods to reduce the chances of reinfestation indoors.

Young people might like to learn more about fire ants in Extension publication ANR-1185, "The Hidden Truth About Red Imported Fire Ants."

References

Holldobbler, Bert, and E. O. Wilson. 1990. The Ants. Belknap Press of Harvard University Press, Cambridge, Mass.

Tashiro, Haruo. 1987. Turfgrass Insects of the United States and Canada. Cornell University Press, Ithaca, NY.

Vinson, S. B. and A. A. Sorensen. 1986. Imported Fire Ants: Life History and Impact. Texas A&M University, College Station, Texas

Use pesticides only according to the directions on the label. Follow all directions, precautions, and restrictions that are listed. Do not use pesticides on plants that are not listed on the label.

The pesticide rates in this publication are recommended only if they are registered with the Environmental Protection Agency and the Alabama Department of Agriculture and Industries. If a registration is changed or canceled, the rate listed here is no longer recommended. Before you apply any pesticide, check with your county Extension agent for the latest information.

For more information, contact your county Extension office. Visit http://www.aces.edu/counties or look in your telephone directory under your county's name to find contact information. Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University) offers educational programs, materials, and equal opportunity employment to all people without regard to race, color, national origin, religion, sex, age, veteran status, or disability.