There are three species of fire ants that are native to the United States. There are two species that were accidentally imported from South America. All of the fire ants live in the warmer southern parts of the United States.
Scientists think that the black imported fire ant, Solenopsis richteri (Forel), was brought to the United States around 1918. It was first reported along the Gulf Coast. However, now it is found in eastern Mississippi, western Alabama, and southern Tennessee.
The red imported fire ant, Solenopsis invicta (Buren), is sometimes called simply RIFA. It arrived along the Gulf Coast in the 19030's or 1940's. Scientists think the ant came in a ship from South America. They suspect the ship may have been loaded with soil that was being used as ballast. This ant is now established from the Carolinas to California. It has been found as far north as Kansas and Maryland.
The red imported fire ants are very aggressive. The colonies are very large and therefore the workers must find a lot of food. Because of these facts, the red imported fire ant has displaced many other ant species as it expanded its territory across the southern states.
The red imported fire ant has had an economic impact in every area where it has been introduced. It has affected cattle and livestock production. It has affected deer and other wildlife. This ant has affected quail, prairie chickens, wild turkeys, and many other ground-nesting birds.
The ants are attracted to electric equipment. There have been several blackouts that were caused by fire ants short-circuiting equipment. The ants also create a hazard for the maintenance workers who must repair the electrical equipment.
Scientists believe the red imported fire ant has been able to migrate by a combination of three methods. The first method is by the colony's natural growth. As the colony grows, it requires a bigger area to forage for food. This method of expansion is fairly slow, but it is relentless. A colony of red imported fire ants eventually eliminates almost all competition in its territory.
The second method of expansion is by annual mating flights. When a colony is mature, it produces winged reproductive ants. Scientists call them alates. During the summer, these male and female ants leave the nest where they developed. Because they fly out in a swarm, many people call them swarmers. These winged ants mate with swarmers from other colonies. After mating, the females pick a nest site and start new colonies.
The third method of expansion has been much more efficient. Scientists found that people have spread the red imported fire ant. These ants have been found in truckloads of sod, in shipments of nursery stock, and in shipments of baled hay. Red imported fire ants have also been found in shipments of household goods that belong to families that are relocating.