The red imported fire ant (Solenopsis invicta) is an established invasive species that is known for aggressively defending their nests and delivering painful stings that leave a burning sensation. They are originally from South America, and have successfully established in various parts of the world. This article explores the swarming behavior of red imported fire ants within the landscape, as well as effective strategies for their control.

Recently, you may have seen a fire ant queen crawling on the sidewalk or ground. Red imported fire ants exhibit swarming behavior, whereby usually after a rainfall, alates or reproductive individuals take flight simultaneously and form mating aggregations. These swarms consist of winged male and female ants and they mate while in mid-air. This flight behavior facilitates dispersal and establishment of new colonies. However, fire ants cannot fly far unless they are carried by wind. When flying, queens search for areas with high light reflectance, such as bodies of water or metallic objects. Upon landing, a mated female removes her wings and searches for a suitable nesting site. Male alates parish shortly after mating. Red imported fire ants actively move within the landscape and are accidentally transported by human-assisted means. The ants establish nests in a wide range of habitats such as open fields, forests, and urban environments. Red imported fire ants build large mounds and complex underground nests, which consist of interconnected tunnels and chambers. These nests can extend several feet below the surface, providing protection and allowing the ants to forage over large areas. The mounds themselves do not have entrance or exit holes that can be viewed from the surface.

Adult worker fire ant.

Red imported fire ants are highly adaptable and can exploit many food sources. They are omnivorous, feeding on small invertebrates, seeds, fruits, and even carrion. This versatility enables them to thrive and makes true eradication efforts challenging, if not impossible. Given the need to feed a high number of individuals in a colony, red imported fire ants can be incredibly disruptive to ecosystems. The negative impacts of red imported fire ants on agriculture, ecosystems, and human health, requires effective control strategies. The use of insecticides is a widely used approach to manage fire ants in the area of usage. Ideally, fire ant mounds should be treated with an insecticidal bait, and then after one week the bait should be wetted to facilitate movement of the product into the mound.

Insecticide sprays can also be effective. Using a pressure sprayer to apply liquid insecticide to a mound allows for further penetration of the product. Alternatively, if a pressure sprayer is not available, mounds can be drenched with liquid insecticide, however, more product will need to be applied in order to ensure penetration into the nest. Broadcast treatments of bait or spray products, which cover large areas, and mound-specific treatments can be effective. However, this strategy can impact off target beneficial insects and other wildlife. Be sure to follow all label directions, use products permitted for red imported fire ants, and products should be approved for the type of environment requiring treatment. If it is about to rain or the soil is saturated with water, do not apply insecticide.

~Dr. Aaron Ashbrook

Comparative images of red imported fire ant male alate, queen alate and a sterile worker ant.