Overview
RIFAs are more aggressive than most native ant species, and have a painful sting. An animal, including humans, typically encounters them by inadvertently stepping into one of their mounds, which causes the ants to swarm up the legs, attacking en masse. The ants respond to pheromones released by the first ant to attack and sting in concert, often killing smaller animals by overloading their immune systems.
RIFAs compete successfully against other ants, and have been enlarging their range.
They are a pest, not only because of the physical pain they can inflict, but also because their mound-building activity can damage plant roots, lead to loss of crops, and interfere with mechanical cultivation. It is not uncommon for several fire ant mounds to appear suddenly in a suburban yard or a farmer's field, seemingly overnight. Their stings are rarely life-threatening to humans and other large animals, causing only 80 documented deaths as of 2006. However, they often kill smaller animals, such as birds. They sometimes kill newborn calves if they do not get on their feet quickly enough. The sting of the RIFA has venom composed of a necrotizing alkaloid, which causes both pain and the formation of white pustules that appear one day after the sting.
Fire ants are excellent natural predators and are biological controls for pests such as the sugarcane borer, the rice stink bug, the striped earwig, aphids, the boll weevil, the soybean looper, the cotton leafworm, the hornfly, and many other pests harmful to crops. However, they also kill beneficial pollinators, such as ground-nesting bee species. Seeds, fruits, leaves, roots, bark, nectar, sap, fungi, and carrion are all fire ant prey, and they are not shy about creating their own carrion, either. They are proficient enough at overwhelming intruders that they can virtually clear an area of invertebrates, lizards, and ground-dwelling birds.
Red imported fire ants are extremely resilient, and have adapted to contend with both flooding and drought conditions. If the ants sense increased water levels in their nests, they will come together and form a huge ball or raft that is able to float, with the workers on the outside and the queen inside. Once the ball hits a tree or other stationary object, the ants swarm onto it and wait for the water levels to recede. To contend with drought conditions, their nest structure includes a network of underground foraging tunnels that extends down to the water table. Also, although they do not hibernate during the winter, colonies can survive temperatures as low as 16 °F (−9 °C).
RIFAs were the first clearcut case discovered of a green-beard gene, by which natural selection can favor altruistic behavior.
Read more about this topic: Red Imported Fire Ant