Fire Ants

The red imported fire ant, Solenopsis invicta, a native of southern Brazil, currently inhabits 9 southern states. These areas are currently under quarantine by the U.S. Department of Agriculture (USDA) regulating the export of certain items that might carry ant infestations to other parts of the country.

Infestation Expansion

Even if you are not currently in a quarantined area, you should be aware of how fire ants will affect you and how you can control them because fire ant infestation is expanding.

The ants expand naturally and steadily into new territory because of their high reproductive rate; mild winter weather has accelerated their movement. Current technology and efforts are not expected to reverse this growth trend in the foreseeable future. In addition, long- distance movement sometimes occurs because of human activities, primarily the transport of fire- ant-infested nursery plants and sod into areas outside of the federal and state quarantine zone.

Commercial and Public Impact

From an agricultural perspective, red imported fire ants are nuisances primarily because they annoy field workers and because their mounds may damage harvesting equipment. Livestock injury and crop damage are usually minor.

Fire ants have a much greater impact on the ornamental plant, sod, and landscaping industries because of problems associated with shipping infested plant material into uninfested areas of the country. Mounds discovered in previously uninfested areas frequently can be traced to landscaping performed at commercial and industrial developments.

For the general public, 2 aspects of red imported fire ant infestations are particularly annoying: the unsightly mounds formed in lawns and yards and the painful stings received when mounds are disturbed. Within 24 hours after a person is stung, a pustule-like sore forms at each sting site, which usually itches intensively. Scratching the pustule may rupture the skin, leading to secondary infection and scarring. A small proportion of people stung are highly allergic to fire ant stings and require immediate medical attention.

As red imported fire ants spread into more populated areas, more people are likely to be stung. Encounters with fire ants can be expected not only outdoors but indoors as well. In southern states foraging ants have invaded private residences and buildings such as offices, hospitals, and nursing homes. In these situations, fire ant control is more critical and potentially more difficult because of concerns related to both the ants and the indoor use of chemical insecticides.

Identification

Adult red imported fire ants are reddish to dark brown and occur in five forms: (1) minor workers, about 1/8 inch long; (2) major workers, about 1/4 inch long; (3) winged males and (4) females, each about 1/3 inch long; and (5) queens, about 1/3 inch long.

Fire ant mounds vary in size, usually in direct proportion to the size of the colony. For example, a mound that is 2 feet in diameter and 18 inches high may contain about 100,000 workers, several hundred winged adults, and one queen. (the image above shows a typical red imported fire ant mound.) In addition, when the mound of an active fire ant colony is broken open, whitish rice grain-like larvae and pupae usually can be found. These immature ants will eventually develop into workers or winged adults. Mounds constructed in clay soils are usually symmetrical and dome-shaped; mounds built in sandy soils tend to be irregularly shaped.

Reproduction

During the spring and summer, winged males and females leave the mound and mate in the air. After mating, females become queens and may fly as far as 10 miles from the parent colony. However, most queens descend to the ground within much shorter distances. Only a very small percentage of queens survive after landing. Most queens are killed by foraging ants, especially other fire ants. If a queen survives, she sheds her wings, burrows into the ground, and lays eggs to begin a new colony. In the late fall, many small colonies of fire ants will appear. Many of the colonies will not survive the winter unless the weather is mild.

Eating Habits

Fire ants prefer oily and greasy foods. They also feed on many other insects and, from that standpoint, could be considered beneficial. To find food, workers forage around their mound. These ants usually travel in underground tunnels that radiate from the mound. If the mound is disturbed. ants swarm out and sting the intruder.

Treatment Outdoors

Because fire ants cannot be eradicated over wide areas, the goals of insecticide treatment are to eliminate fire ants in areas where the risk to people is high and to reduce infestations to acceptable levels. There are two approaches to the chemical control of fire ants. An insecticide can be applied to individual mounds or it may be broadcast over a wide area infested with fire ant colonies.

Mound-specific treatments are usually more environmentally and ecologically acceptable because they require only a fraction of the insecticide needed for broadcast treatments. Regardless of the method used, the objective is to kill the queen, because she is the only ant in the colony capable of laying eggs. Label directions should always be followed when applying any fire ant insecticide.

MOUND TREATMENTS

Individual mounds may be treated with a liquid drench of insecticide or an insecticidal bait.

Drenches

Mound drenches, which are insecticides diluted with water, work as contact insecticides. To be effective, the drench must trickle down through the mound and contact most of the fire ants. Ants contacted by the drench die in less than 24 hours. Drenches should be used when the risk of human contact with fire ants is high and the fire ant infestation must be eliminated immediately. High-risk areas include home lawns, school grounds, parks, and other areas frequently used by the public.

Best control usually results in spring and fall when temperatures are between 70 and 85 F. Control with drench treatments is more difficult to achieve during very hot summer months because the ants remain deep within their mounds and are hard to reach with liquid insecticides.

The following procedure is recommended for drenching mounds.

•Following label directions, pour the correct amount of water into a bucket or sprinkler can. Add the prescribed amount of insecticide, mix well (without splashing), then gently pour the diluted insecticide over the surface of the mound. Apply the drench at a rate of approximately 1 gallon per 6 inches of mound diameter. At this rate, for example, a mound measuring 12 inches across would receive 2 gallons of insecticide drench. The amount of drench applied is more important than the concentration of insecticide in the drench.

•Thoroughly wet the ground to a distance of about 2 feet around the mound.

•Sometimes the drench does not kill all fire ants in a treated colony. The surviving ants will construct small mounds within 10 to 15 feet of the parent colony. Several days after the application, search the area around the treated colony for new mounds and treat them with the insecticide drench.

•Keep children and pets away from the treated area until it is dry.

Baits

Ant baits also can be used to treat individual mounds. Baits are insecticides that have been mixed with ant attractants. Worker ants carry particles of the bait back to the mound and feed them to the queen. Although the insecticide kills the queen, workers may be active inside the mound for several weeks before the colony finally disappears.

Baits are fairly slow acting but easier to apply than mound drenches. Therefore, they are best used in situations where many mounds must be treated, when water for mixing mound drenches is difficult or impossible to obtain, or when the risk of human contact is low and there is no urgent need to eliminate the infestation.

The active ingredients in ant baits are rapidly degraded by high temperature, high humidity, and intense sunlight. The baits can be rendered ineffective in a few hours by these conditions. Follow this procedure when using baits.

•Apply the bait according to label directions. Sprinkle the recommended amount around each mound but not on the mound itself. It is best to apply the bait in the early evening.

•Most bait labels state that the material should not be applied within 6 hours after precipitation occurs (either rainfall or heavy dew). Moisture tends to make the bait's attractant oils rancid and less appealing to foraging ants.

BROADCAST APPLICATIONS

Broadcast treatment is the distribution of an insecticidal bait over a large infested area containing many fire ant colonies. One disadvantage is that broadcast treatments can disrupt native ant communities as well as fire ant infestations. Broadcast treatments can result in an ant community changing from one that is dominated by native ants to one dominated by fire ants. On the other hand, in areas with very high mound densities, broadcast applications allow large areas to be treated quickly.

Areas of high public use can be protected by spring and fall broadcast applications of ant bait. If the area becomes reinfested with fire ants during the summer months, individual mounds can be treated with an insecticide drench or ant bait, although as noted previously control is more difficult when temperatures are high.

Indoors

The key to reducing the threat of fire ant infestations indoors is prevention, which means removing exposed food sources that may attract these insects. If fire ants enter a building, the treatment objective must be to reduce the potential for accidental stings as quickly as possible. Insecticides labeled for indoor use, particularly pyrethroids, can be used in homes and public buildings to drive foraging ants outside or away from high-use or critical areas, such as kitchens, recreation rooms, patient rooms, operating rooms, or intensive care units.

Although baits work well for many ants that invade buildings, they should not be used to control fire ants indoors because they are more likely to attract additional fire ants, increasing the chance that an occupant will be stung. For this reason, it is important to positively identify fire ants as the pest in question before applying any control measures. Ultimately, long-term control of fire ants indoors can be achieved only by locating and treating their mound or mounds, preferably with an insecticide drench.

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