|Red imported fire ant|
|A group of fire ant workers|
The red imported fire ant (Solenopsis invicta), also known as the fire ant or RIFA, is a species of ant native to South America. A member of the genus Solenopsis in the subfamily Myrmicinae, it was described by Swiss entomologist Felix Santschi as a variant in 1916. Its current specific name invicta was given to the ant in 1972 as a separate species. However, the variant and species were the same ant, and the name was preserved due to its wide use. Though South American in origin, the red imported fire ant has been accidentally introduced in Australia, New Zealand, several Asian and Caribbean countries, and the United States. The red imported fire ant is polymorphic, as workers appear in different shapes and sizes. The ant's colours are red and somewhat yellowish with a brown or black gaster, but males are completely black. Red imported fire ants are dominant in altered areas and live in a wide variety of habitats. They can be found in rain forests, disturbed areas, deserts, grasslands, alongside roads and buildings, and in electrical equipment. Colonies form large mounds constructed from soil with no visible entrances because foraging tunnels are built and workers emerge far away from the nest.
These ants exhibit a wide variety of behaviours, such as building rafts when they sense that water levels are rising. They also show necrophoric behaviour, where nestmates discard scraps or dead ants on refuse piles outside the nest. Foraging takes place on warm or hot days, although they may remain outside at night. Workers communicate by a series of semiochemicals and pheromones, which are used for recruitment, foraging, and defence. They are omnivores and eat dead mammals, arthropods, insects, seeds, and sweet substances such as honeydew from hemipteran insects with which they have developed relationships. Predators include arachnids, birds, and many insects including other ants, dragonflies, earwigs, and beetles. The ant is a host to parasites and to a number of pathogens, nematodes, and viruses, which have been viewed as potential biological control agents. Nuptial flight occurs during the warm seasons, and the alates may mate for as long as 30 minutes. Colony founding can be done by a single queen or a group of queens, which later contest for dominance once the first workers emerge. Workers can live for several months, while queens can live for years; colony numbers can vary from 100,000 to 250,000 individuals. Two forms of society in the red imported fire ant exist: polygynous colonies (nests with multiple queens) and monogynous colonies (nests with one queen).
Venom plays an important role in the ant's life, as it is used to capture prey or for defence. About 95% of the venom consists of water-insoluble piperidine alkaloids known as solenopsins, with the rest comprising a mixture of toxic proteins that can be particularly potent in sensitive humans. More than 14 million people are stung by them in the United States annually, where many are expected to develop allergies to the venom. Most victims experience intense burning and swelling, followed by the formation of sterile pustules, which may remain for several days. However 0.6% to 6.0% of people may suffer from anaphylaxis, which can be fatal if left untreated. Common symptoms include dizziness, chest pain, nausea, severe sweating, low blood pressure, loss of breath, and slurred speech. More than 80 deaths have been recorded from red imported fire ant attacks. Treatment depends on the symptoms; those who only experience pain and pustule formation require no medical attention, but those who suffer from anaphylaxis are given epinephrines. Whole body extract immunotherapy is used to treat victims and is regarded as highly effective.
The ant is viewed as a notorious pest, causing billions of dollars in damages annually and impacting wildlife. The ants thrive in urban areas, so their presence may deter outdoor activities. Nests can be built under structures such as pavements and foundations, which may cause structural problems, or cause them to collapse. Not only can they damage or destroy structures, but red imported fire ants also can damage equipment and infrastructure and impact business, land, and property values. In agriculture, they can damage crops and machinery, and threaten pastures. They are known to invade a wide variety of crops, and mounds built on farmland may prevent harvesting. They also pose a threat to animals and livestock, capable of inflicting serious injury or killing them, especially young, weak, or sick animals. Despite this, they may be beneficial because they consume common pest insects on crops. Common methods of controlling these ants include baiting and fumigation; other methods may be ineffective or dangerous. Due to its notoriety and importance, the ant has become one of the most studied insects on the planet, even rivalling the western honey bee (Apis mellifera).
The specific epithet of the red imported fire ant, invicta, derives from Latin, and means "invincible" or "unconquered". The epithet originates from the phrase Roma invicta ("unconquered Rome"), used as an inspirational quote until the fall of the Western Roman Empire in 476 AD. The generic name, Solenopsis, translates as "appearance" or "face" from Ancient Greek. It is a compound of two Ancient Greek words–solen, meaning "pipe" or "channel", and opsis, meaning "appearance" or "sight". The ant is commonly known as the "red imported fire ant" (abbreviated as RIFA), because of the burning sensation caused by its sting. Alternative names include: the "fire ant", "red ant" or "tramp ant". In Brazil, locals call the ant toicinhera, which derives from the Portuguese word toicinho (pork fat).
The red imported fire ant was first described by Swiss entomologist Felix Santschi in a 1916 journal article published by Physis. Originally named Solenopsis saevissima wagneri from a syntype worker collected from Santiago del Estero, Argentina, Santschi believed the ant was a variant of S. saevissima; the specific epithet, wagneri, derives from the surname of E.R. Wagner, who collected the first specimens. The type material is currently housed in Naturhistorisches Museum Basel, Switzerland, but additional type workers are possibly housed in the Muséum national d'histoire naturelle, Paris. In 1930, American myrmecologist William Creighton reviewed the genus Solenopsis and reclassified the taxon as Solenopsis saevissima electra wagneri at infrasubspecific rank, noting that he could not collect any workers that referred to Santschi's original description. In 1952, the S. saevissima species complex was examined and, together with nine other species-group names, S. saevissima electra wagneri was synonymised with S. saevissima saevissima. This reclassification was accepted by Australian entomologist George Ettershank in his revision of the genus and in Walter Kempf's 1972 catalogue of Neotropical ants.
In 1972, American entomologist William Buren described what he thought was a new species, naming it Solenopsis invicta. Buren collected a holotype worker from Cuiabá in Mato Grosso, Brazil, and provided the first official description of the ant in a journal article published by the Georgia Entomological Society. He accidentally misspelled invicta as invica above the description pages of the species, although it was clear that invicta was the intended spelling because of the constant use of the name in the article. The type material is currently housed in the National Museum of Natural History, Washington, D.C.
In a 1991 review of the species complex, American entomologist James Trager synonymised S. saevissima electra wagneri and S. wagneri together. Trager incorrectly cites Solenopsis saevissima electra wagneri as the original name, erroneously believing that the name S. wagneri was unavail