Taxonomic name: Solenopsis invicta Buren, 1972
Synonyms: Solenopsis saevissima var. wagneri (Santschi), Solenopsis wagneri (Santschi)
Common names: fourmi de feu (French), red imported fire ant (RIFA) (English), rote importierte Feuerameise (German)
Organism type: insect
Solenopsis invicta is an aggressive generalist forager ant that occurs in high densities and can thus dominate most potential food sources. They breed and spread rapidly and, if disturbed, can relocate quickly so as to ensure survival of the colony. Their stinging ability allows them to subdue prey and repel even larger vertebrate competitors from resources.
Workers in the Solenopsis genus are polymorphic, meaning they are physically differentiated into more than two different body-forms (Holway et al. 2002). Fire ants are quite small, varying from 2 - 6mm in length, and are predominantly reddish-brown in colour. Their nests vary in shape and size, but all have a honeycomb-like internal structure and are usually found in open areas including lawns, pastures, along roadsides and abandoned cropland. They may be 40cm high dome-shaped mounds without any obvious entrance/exit. Mounds may not be evident at all. The red imported fire ant should not be confused with those species which are commonly called fire ants.
Please click on AntWeb: Solenopsis invicta for more images and assistance with identification. The AntWeb image comparison tool lets you compare images of ants at the subfamily, genus, species or specimen level. You may also specify which types of images you would like to comare: head, profile, dorsal, or label.
Please see PaDIL (Pests and Diseases Image Library) Species Content Page Ants: Red imported fire ant for high quality diagnostic and overview images.
Please follow this link for a fully illustrated Lucid key to common invasive ants [Hymenoptera: Formicidae] of the Pacific Island region [requires the most recent version of Java installed]. The factsheet on Solenopsis invicta contains an overview, diagnostic features, comparision charts, images, nomenclature and links. (Sarnat, 2008)
agricultural areas, coastland, desert, natural forests, planted forests, range/grasslands, riparian zones, ruderal/disturbed, scrub/shrublands, urban areas, water courses
S. invicta is a “hot climate specialist” and inhabits hot arid regions. Cold climates are unsuitable for its successful establishment in native ecosystems. However, it may survive in such climates in human habitations or infrastructure (such as climate-controlled buildings or greenhouses). Although its capacity for local spread will be restricted its continued presence is a threat as it provides a source from which long distance spread can occur (McGlynn 1999; Holway et al. 2002). It is estimated that continental areas receiving more than 510mm of precipitation per year will support S. invicta while areas receiving less than this will only support populations of the ant near sources of permanent water or in regularly irrigated areas. These include lakes, rivers, springs, lawns or agricultural areas (Morrison et al 2004).
Both the red imported fire ant and the tropical fire ant (S. geminata) are more likely to colonise open environments and are opportunistic exploiters of human associated habitats, such as the ones previously mentioned (Holway et al. 2002).
In general, invasive ants are usually more likely to establish in disturbed habitats, including the edges of forests or agricultural areas (Ness and Bronstein 2004). Deforested areas are particularly at risk of becoming colonised by red imported fire ants (Morrison et al 2004). S. invicta constructs earthen mounds for the purposes of brood thermoregulation, which are easier to build in open, sunny areas; so it is less abundant in, and in general poses a smaller threat to, densely wooded forest habitats (Tschinkel 1993; Porter and Tschinkel 1993, in Morrison et al 2004). Tropical regions that are warm and wet, but also densely forested do not represent a suitable habitat for fire ants (Morrison et al 2004).
Please read Invasive ants impacts for a summary of the general impacts of invasive ants, such as their affect on mutualistic relations, the competitive pressure they impose on native ants and the effect they may have on vulnerable ecosystems.
There is conflicting evidence as to whether S. invicta inhibits the dispersal of ant-dispersed plants. In some cases, it may interrupt and reduce dispersal by competing with native ant dispersers, eating seeds whole or in-effectively dispersing seeds (ie: by leaving them exposed on the soil surface rather than protecting them by seed-burial). S. invicta may increase or decrease the survival of plant, depending on the species and other biotic variables. They may benefit a plant by killing, or at least deterring, insects that damage the plant (such as plant-feeding insects). Alternatively, or in addition, they may reduce numbers of insects that benefit the plant, such as plant mutualists that protect the plant or disperse plant seeds or carnivorous insects (that prey on plant-feeding insects). In fact, S. invicta is a notable example of an invasive ant which has negative effects on such insects, because it prefers a protein-rich diet (Ness and Bronstein 2004).
S. invicta reduces biodiversity among invertebrates and reptiles, and may also kill or injure frogs, lizards or small mammals. In particular the red imported fire ant has the potential to devastate native ant populations (McGlynn 1999). It is competitively dominant to most other invasive ant species; it has displaced the Argentine ant (Linepithema humile), but not Monomorium minimum, in areas in the USA where the species have been introduced (Holway et al. 2002). In the USA, it has been found to negatively impact at least fourteen bird species, thirteen reptile species, one fish species and two small mammal species (through predation, competition and/or stinging) (Holway et al. 2002). The current economic impact of S. invicta on humans, agriculture, and wildlife in the United States is estimated to amount to at least half a billion, if not several billion, dollars per year (Thompson et al. 1995, Thompson and Jones 1996, in Morrison et al 2004).
S. invicta may impact social and economic activities at all levels. They can sting people and may cause an allergic reaction. Public areas such as parks and recreational areas may become unsafe for children. They may infest electrical equipment (such as computers, swimming pool pumps, cars or washing machines) becoming a nuisance, or even a danger, to people. Agricultural impacts may include damage to crops, interference with equipment and the stinging of workers in the field. The costs associated with S. invicta in the United States, for example, have been estimated at $1 billion per year (Pimentel et al. 2000, Tsutsui and Suarez 2003). The Australian Bureau of Agriculture Resources Economics has estimated the losses procured in rural industries to amount to more than AU $6.7 billion over 30 years. According to a professor at the Texas Agricultural Extension (USA) the agricultural economic losses caused by the ant are an estimated US $90 million annually. In Texas at least US $580 million was spent in 2000 to control this pest. Gutrich et al. (2007) undertook a study to estimate the potential economic costs to Hawaii, in case of the introduction and establishment of the red imported fire ant. The authors of the study conclude that the estimated impact on various economic sectors in Hawaii would be around US $ 211 million/year.
Click here for Information about the relation between colony structure and level of threat
The mound-building activities of non-native Solenopsis spp. alter physical and biogeochemical properties of soils, and can lead to increased soil aerationand infiltrability, elevated soil pH, increased phosphorous and potassium levels, lowered surface soil bulk density, change in organic matter, altered soil texture and enhanced fungal abundance. These influences are further enhanced by plant uptake and excretion in the rhizosphere, and cause other flow-on effects within ecosystems. This an area that has not been well studied, and more research is warranted (DeFauw et al. 2008 and references therein).
In northern Alabama and Mississippi, where their ranges overlap the red imported fire ant (S. invicta) is known to hybridise with the black imported fire ant (S. richteri) (Holway et al. 2002).
Native range: The red imported fire ant is native to South America (Holway et al. 2002).
Known introduced range: It has been introduced into parts of Australia and North America. It has also been introduced onto some vulnerable island ecosystems including islands in the Caribbean (Puerto Rico and the Virgin Islands) and the Pacific (New Zealand) (McGlynn 1999; Holway et al. 2002). Morrison et al (2004) determined the potential global range expansion of S. invicta based on precipitation and temperature data and temperature-based predictions. The authors concluded that large areas in the New World including Mexico, Central America and many Caribbean islands are at great risk of invasion by the ant. The northern part of South America may also be susceptible."
Introduction pathways to new locations
Agriculture: The movement of agricultural equipment or associated plants and planting material within or from infested areas risks the spread of the red imported fire ant, which often colonises these microhabitats in disturbed areas.
Aquaculture: Fire ants are found near areas of permanent water, such as dams, rivers, ponds and aquaculture containers. Because of this they may be spread by the associated trade industries.
Nursery trade: Fire ants often establish themselves in pot-plants in contact with the ground, in stores of topsoil, mulch and potting mixes and under landscaping materials.
Translocation of machinery/equipment: The red imported fire ant is able to rapidly colonise disturbed areas and may be spread by the movement of soil or plant material (Morrison et al 2004). Deforested areas are at great risk considering the high level of movement of materials and equipment to and from such sites and the suitability of the disturbed environment for fire ant establishment.
Transportation of habitat material: The red imported fire ant is able to rapidly colonise disturbed areas and may be spread by the movement of soil or plant material (Morrison et al 2004). Deforested areas are at great risk considering the high level of movement of materials and equipment to and from such sites and the suitability of the disturbed environment for fire ant establishment.
Local dispersal methods
Agriculture (local): The movement of agricultural equipment or associated plants and planting material within or from infested areas risks the spread of the red imported fire ant, which often colonises these microhabitats in disturbed areas.
Aquaculture (local): Fire ants are found near areas of permanent water, such as dams, rivers, ponds and aquaculture containers. Because of this they may be spread by the associated trade industries.
Natural dispersal (local): Winged dispersal of reproductive females is rare in uniclonal colonies of the red imported fire ant. Such colonies grow outwards and eventually “bud” off into separate colonies. In the USA this type of colony has been reported to spread up to 40 metres a year. However, red imported fire ants may also be multiclonal, and in this situation the production, by the colony, of winged reproductive females is common. Because of this, colonies may spread across wider distances, and faster (Holway et al. 2002).
Natural dispersal (local): Fertile females and males called alates go on mating flights during the warmer months when conditions are suitable. Mating takes place in the air and the fertilised females can then start new colonies. New nests may not be visible for several months.
Translocation of machinery/equipment (local): The red imported fire ant is able to rapidly colonise disturbed areas and may be spread by the movement of soil or plant material (Morrison et al 2004). Deforested areas are at great risk considering the high level of movement of materials and equipment to and from such sites and the suitability of the disturbed environment for fire ant establishment.
Transportation of habitat material (local): Particularly garden or potted plants.
Transportation of habitat material (local): The red imported fire ant is able to rapidly colonise disturbed areas and may be spread by the movement of soil or plant material (Morrison et al 2004). Deforested areas are at great risk considering the high level of movement of materials and equipment to and from such sites and the suitability of the disturbed environment for fire ant establishment.
Water currents: The red imported fire ant “rafts” in response to flooding, allowing it to live in watered urban environments (Holway et al. 2002). Flooding may stimulate local ant dispersal.
Preventative measures: Early detection by active surveillance and subsequent nest treatment is the best way to prevent any ant species from establishing in novel environments. Pitfalls and attractant baits are both methods that can yield good results.(Simon O'Connor pers.comm). The Pacific Ant Prevention Programme is a proposal prepared for the Pacific Plant Protection Organisation and Regional Technical Meeting for Plant Protection. This plan aims to prevent the red imported fire ant and other invasive ant species with economic, environmental or social impacts from establishing within or spreading between countries in the Pacific.
Integrated management: The potential of invasive ants to reach high densities is greater in human-modified ecosystems; this is particularly evident with respect to land that is intensely utilised for primary production. For example, the little fire ant (Wasmannia auropunctata) is a great problem in areas in its native South America that have been over-exploited by humans, including in sugarcane monocultures and cocoa farms in south Colombia and Brazil, respectively (Armbrecht and Ulloa-Chacón 2003). Similarly, the Argentine ant (Linepithema humile) reaches high densities in agricultural systems such as citrus orchards (which host mutualistic honeydew producing insects) (Armbrecht and Ulloa-Chacón 2003; Holway et al. 2002). Improved land management, including a reduction in monoculture and an increase in the efficiency of primary production, may help invasive ant prevent population explosions (alleviating the problems caused by high densities of ants) and could reduce potential sources from which new infestations could occur.
Biological: Parasitic phorid flies have been introduced to control S. invicta. Multiple species of these parasitic flies (originally from Argentina and Brazil) have been released by researchers at the Brackenridge Field Laboratory (BFL). The fly larvae develop inside the ants and kill their host. Pseudacteon tricuspis, was introduced to several locations in Texas beginning in 1999 with BFL in central Austin. Flytraps have been used to map the spread of the first species of phorid fly introduced. It is found that the inrtroduced phorid flies have spread to more than 12 counties and 3.5 million acres in Central Texas and seven counties and 1.5 million acres in the Coastal Bend region of Texas, speading at 3 to ten miles per year from the initial introduction areas. Two other phorid flies have been introduced since 2004. For more details please see Using phorid flies in the biocontrol of imported fire ants in Texas.
For details on preventative measures, chemical and biological control options, please see management information.
The red imported fire ant may gain nutrition from includes invertebrates, vertebrates and plants, and oily or sugary foods. However it is known to prefer protein-rich food sources and may be a great consumer of insects (Ness and Bronstein 2004). Studies suggest that S. invicta is not a great consumer of extra-floral nectar and rarely collects it (McLain 1983, in Ness and Bronstein 2004). S. invicta possess a venomous sting that increases its ability to consume large invertebrates (and potentially small vertebrates) (Holway et al. 2002). In terms of bait preference, the red imported fire ant prefers solid and protein-rich baits (Stein et al. 1990, Cherry and Nuessly 1992, Brinkman et al. 2001, in Ness and Bronstein 2004).
The queen produces from 800 to 2000 eggs per day. She produces sterile worker females and occasionally fertile females and males. Fertilised females may start new colonies. Uniclonal colonies are known to establish new colonies by budding. A queen or queens leave the nest with a cohort of workers, larvae, etc. and start a new colony. Mature fire ant colonies may contain up to 400,000 worker ants.
This species has been nominated as among 100 of the "World's Worst" invaders
Reviewed by: Neil Reimer, Ph.D. Plant Quarantine Branch Chief Hawaii Department of Agriculture
Compiled by: IUCN/SSC Invasive Species Specialist Group (ISSG) with support from the Ministry of Agriculture and Forestry (MAF)- Biosecurity New Zealand
Updates with support from the Overseas Territories Environmental Programme (OTEP) project XOT603, a joint project with the Cayman Islands Government - Department of Environment
Last Modified: Monday, 4 October 2010