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Solenopsis richteri Forel, 1909
"black imported fire ant (BIFA)"

Authors: Joe A. MacGown and Ryan J. Whitehouse
Uploaded 2009; last updated on 15 August 2016

Solenopsis richteri, full face view of a major worker
Solenopsis richteri, profile view of a major worker
Solenopsis richteri, full face view of a major worker, note the black scapes
Solenopsis richteri, profile view of a major worker
Solenopsis richteri, full face view of a major worker
Solenopsis richteri, profile view of a major worker
Solenopsis richteri, full face view of a major worker, note the black scapes
Solenopsis richteri, profile view of a major worker
Solenopsis richteri, profile view of a minor worker
Solenopsis richteri, profile view of an alate male
Solenopsis richteri, profile view of a minor worker
Solenopsis richteri, profile view of an alate male

The genus Solenopsis includes both the "fire ants", known for their aggressive nature and potent sting, and the minute "thief ants", many of which are lestobiotic subterranaen or arboreal species that are rarely collected. Many species may be polygynous.

Generic level identification of Solenopsis is relatively straight forward, although sizes are greatly variable ranging from approximately 1.0 mm to over 4.0 mm. The genus can be basically characterized by the following: mandible with four teeth (usually), bicarinate clypeus with 0-5 teeth, median part of clypeus with a pair of longitudinal carinae medially or at lateral edges, 10-segmented antennae that terminates in a distinctive 2-segmented club, overall shiny appearance and general lack of or reduced sculpture (when present usually restricted to rugulae or striae on the head, alitrunk, petiole, and postpetiole), lack of propodeal spines or other protuberances on the alitrunk, well developed petiole and postpetiole, and a well-developed sting. Workers are either polymorphic (especially in the fire ant group) or monomorphic (especially thief ants).

Hybridization is not uncommon among the larger fire ant group, which can make identification of some species difficult. Identification of thief ants is perhaps even more challenging due to their minute size, similar appearance of workers of one species to another, taxonomic problems, and lack of knowledge of all castes.

Solenopsis richteri, commonly referred to as the black imported fire ant, is a serious econimic pest in both Mississippi and Alabama. This ant can generally be recognized by their large mounds, polymorphic castes (varying sizes of workers), and 10-segmented antennae ending in a 2-segmented club. However, because S. richteri hybridizes with S. invicta, it can be a challenge to differentiate them from the hybrid, which may have characters of both species. The most reliable method for identification of this group is a cuticular hydrocarbon test, which some labs are now equipped to do. Imported fire ant is a major agricultural and urban pest that also causes both medical and environmental harm resulting in a cost of many millions of dollars per year for southeastern states.

Taxonomic History (provided by Barry Bolton, 2013)
Solenopsis Pylades var. Richteri Forel, 1909: 267 (w.q.) ARGENTINA. Neotropic.
Creighton, 1930: 87 (m.); Wheeler & Wheeler, 1977: 589 (l.). Subspecies of Solenopsis saevissima: Santschi, 1916: 379; Creighton, 1950: 232; Wilson, 1952: 58. Raised to species: Buren, 1972: 4. Senior synonym of Solenopsis tricuspis: Creighton, 1930: 87; of Solenopsis oblongiceps: Trager, 1991: 187. See also: Rhoades, 1977: 1.

Worker: HL 1.30-1.46mm, HW 1.19-1.39mm, SL 1.04-1.13mm, EL 0.20-0.23mm, MeSL 1.52-1.65 (n=5) (MEM specimens). Workers are highly variable in size and are generally brown to dark brown with a large reddish orange colored spot of the first segment of the gaster and with the posterior half black. Head smooth and shining with numerous erect setae; posterior margin with a medial indent; eyes small and located laterally at the midpoint of the head; mandibles with four distinct teeth; median part of clypeus with two carinae; slight median tooth present on the anterior border of the clypeus; antennae 10-segmented with a distinct 2-segmented club. Mesosoma shining and smooth with some striation on the mesoplurae; numerous long, erect setae present; humeral process present on larger workers (lacking in S. invicta); metanotal groove distinct and well defined; lack of spines on the propodeum. Waist is two-segmented with long, erect setae. Gaster smooth and shinning with numerous long, erect setae; distinct sting present.

Biology and Economic Importance
The black imported fire ant is thought to have been introduced into the U.S. from South America, probably Argentina, sometime near 1918. The black imported fire ant along with Solenopsis invicta, the red imported fire ant, which was introduced sometime between 1933 and 1945, have wreaked havoc on the economy of the South. As if these two species were not bad enough, they both can mate with one another producing a hybrid, which is as bad or worse than either the black or red fire ant. Two native fire ants, S. geminata and S. xyloni, have not been collected in either MS or AL in many years and it is thought that the two imported fire ants and their hybrid have out-competed them for resources and effectively driven them out of this area.

Solenopsis richteri tends to be found in the northeastern part of MS and northwestern portions of AL, and northward into TN; whereas, S. invicta is found in the southern halves of both AL and MS and also found in the western portion of MS following the Mississippi River northward (also in several other states), with the hybrid found in a band between the two populations. 

Native Range: Northern Argentina through Uruguay to southern Brazil (Taber, 2000).

Nearctic: United States (,, and MEM).
Neotropical: Argentina, Chile, Paraguay, Uruguay (

U.S. Distribution: AL, AR, MS, NC, TN, VA (,, and MEM).
Southeastern U.S. Distribution: AL, AR, MS, NC, TN ( and MEM).

Funding for the ant work being done by the MEM in Alabama and Mississippi is from several sources including the National Institute of Food and Agriculture, United States Department of Agriculture, under Project No. MIS-012040, the Mississippi Agricultural and Forestry Experiment Station at Mississippi State University, with support from State Project MIS-311080, NSF Grants BSR-9024810 and DFB-9200856, the Tombigbee National Forest (U.S. Forest Service), the Noxubee Wildlife Refuge, Mississippi Natural Heritage Program Research Grant, USDA Forest Service Agreement No. 08-99-07-CCS-010, the William H. Cross Expedition Fund, and primarily by the USDA-ARS Areawide Management of Imported Fire Ant Project. Additionally, special cooperation has been provided by State Parks, National Forests, National Wildlife Refuges, the Natchez Trace Parkway, and from various private landowners in both Alabama and Mississippi.

Literature Cited

Buren, W. F. 1972. Revisionary studies on the taxonomy of the imported fire ants. Journal of the Georgia Entomological Society 7:1-26.

Creighton, W. S. 1930. The New World species of the genus Solenopsis (Hymenop. Formicidae). Proceedings of the American Academy of Arts and Sciences 66:39-151.

Creighton, W. S. 1950. The ants of North America. Bulletin of the Museum of Comparative Zoology 104:1-585.

Forel, A. 1909. Ameisen aus Guatemala usw., Paraguay und Argentinien (Hym.). Deutsche Entomologische Zeitschrift 1909:239-269.

Rhoades, R. B. 1977. Medical aspects of the imported fire ant. Gainesville: University of Florida Press, 75 pp.

Santschi, F. 1916. Formicides sudaméricains nouveaux ou peu connus. Physis (Buenos Aires) 2:365-399.

Taber, S. 2000. Fire Ants. College Station TX: Texas A&M University Press.

Trager, J. C. 1991. A revision of the fire ants, Solenopsis geminata group (Hymenoptera: Formicidae: Myrmicinae). Journal of the New York Entomological Society 99:141-198.

Wheeler, G. C.; Wheeler, J. 1977. Supplementary studies on ant larvae: Myrmicinae. Transactions of the American Entomological Society 103:581-602.

Wilson, E. O. 1952. O complexo Solenopsis saevissima na America do Sul (Hymenoptera: Formicidae). Memórias do Instituto Oswaldo Cruz. Rio de Janeiro 50:49-59.

Extension Fire Ant Site-
Texas A & M Fire Ant Site-
Imported Fire Ants in Tennessee -
Imported Fire Ant and Household Insects (IFAHI) research site-
LSU red imported fire ant research-
Control of the Red Imported Fire Ant -