Pest of the Month: Red Imported Fire Ant
What does it look like?
Adult red imported fire ants are approximately 1/8 to 1/4-inch long, are reddish brown to black, and are characterized by a 10-segmented antenna, a stinger, and a two-segmented pedicel (abdomen). The ants can be easily distinguished from other ants by their rapid movement and aggressive defensive behavior. Fire ant venom, injected by a stinger, causes a burning sensation due to its high concentration of toxins.
Red imported fire ants form colonies consisting of workers, males and females (capable of flight and reproduction), and one or more queens. A single colony may have dozens of queens, each capable of laying up to 1,500 eggs per day. The average colony contains 100,000 to 500,000 workers, whose job it is to protect and feed the queens.
Red imported fire ants build mounds of soft soil. Mounds, the most visible signs of a fire ant infestation, can be found in almost any type of soil. The mounds rarely are larger than 18 inches in diameter. However, the mound is just the tip of the iceberg. Mounds can extend into the ground 20 feet deep or more, with lateral tunnels extending out more than eight feet along the surface of the soil.
Host material and range
Red imported fire ants, Solenopsis invicta, entered this country in the 1920s through the port of Mobile, Ala. Fire ants are now a serious nuisance for more than 40 million people living in the southern United States. Fire ant mounds are most commonly found in open, sunny areas with good soil moistures — pastures, landscape beds, lawns, fairways and cultivated fields are frequently cultivated in the southern United States.
Moisture is critical to fire ant survival. When the weather is hot and dry, they burrow deep into the soil to find moisture and cooler temperatures. When temperatures are cold, they burrow down to stay warm. When temperatures are moderate and the soil is moist, fire ants are active, foraging near the soil surface and building mounds. In general, if it’s a nice day for people to be outside, it’s a nice day for fire ant activity.
Colonies often move from one site to another. Queens need only half a dozen workers to start a new colony, and a new mound can develop several hundred feet from the old site overnight.
Current threat
Fire ants, which currently infest more than 325 million acres across the southern United States, pose a serious and growing public health threat – injuring millions of people each year with their stings. Fire ants currently infest what is known as the “Fire Ant 13” — Arkansas, Alabama, California, Georgia, Florida, Louisiana, North Carolina, Mississippi, New Mexico, Oklahoma, South Carolina, Tennessee and Texas (as well as Puerto Rico). They are also moving north and west into Arizona, Kansas, Kentucky, Maryland, Missouri and Virginia.
Fire ants sting more than 20 million people annually, and can hinder outdoor recreational activities. But fire ants are more than just a painful nuisance. There may be up to 500,000 ants in a colony. When disturbed, hundreds, sometimes thousands of ants, will attack an intruder, inflicting painful stings that cause burning and itching. Fire ants can cause severe allergic reactions in a significant number of people, and, in rare cases, this reaction can be life threatening.
Prevention tips
Colonies present in landscape beds are usually easy to spot. Visually inspect the area to determine the magnitude of infestation. If one or more mounds are present, the area should be professionally treated. Colonies established on lawns are more difficult to diagnose, as turf is frequently mowed and the mounds are small and difficult to spot. If you suspect that you’re lawn is infested with fire ants, call a professional lawn care operator or pest-control professional and request an inspection.
Treatment tips
Nate Royalty, Ph.D., is product development manager insecticides for Bayer Environmental Science, manufacturer of TopChoice insecticide for control of fire ants. TopChoice is a low-dose, non-bait granular insecticide that requires just one annual application by a licensed professional. It controls fire ants for up to one year, eliminating existing infestations and preventing new mounds from forming.
Photos courtesy of Bayer Environmental Science
