Msstate Logo

Subfamily MYRMICINAE
Tribe SOLENOPSIDINI

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, note the black scapes (MS, Tippah Co.) (photo by Ryan Whitehouse and Joe A. MacGown)
Solenopsis richteri, lateral view of a major worker, note the black scapes (MS, Tippah Co.) (photo by Ryan Whitehouse and Joe A. MacGown)
Solenopsis richteri, full face view of a major worker, note the black scapes (MS, Tippah Co.) (photo by Ryan Whitehouse and Joe A. MacGown)
Solenopsis richteri, clypeal area and mandibles. Note the small medial tooth along clypeal margin (MS, Tippah Co.) (photo by Ryan Whitehouse and Joe A. MacGown)
Solenopsis richteri, close up of pronotal region (MS, Tippah Co.) (photo by Ryan Whitehouse and Joe A. MacGown)
Solenopsis richteri, note the humeral bosses of pronotum (MS, Tippah Co.) (photo by Ryan Whitehouse and Joe A. MacGown)
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
Solenopsis richteri, full face view of a major worker, note the black scapes (MS) (photo by Joe A. MacGown)
Solenopsis richteri, profile view of a major worker (MS) (photo by Joe A. MacGown)
Solenopsis richteri, full face view of a major worker, note the black scapes (MS) (photo by Joe A. MacGown)
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, lateral view of a major worker (MS) (photo by Joe A. MacGown)
Solenopsis richteri, lateral view of a minor worker (MS) (photo by Joe A. MacGown)
Solenopsis richteri, lateral view of an alate male (MS) (photo by Joe A. MacGown)
Solenopsis richteri, workers (MS) (photo by Blake Layton)

Introduction
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 ants are 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.

Diagnosis
Workers of S.richteri are polymorphic ranging in size from about 1.0 mm to 4.0 mm in overall length, are brownish black with a reddish brown funiculus and a reddish color spot on first gastral tergite; have a 10-segmented antenna that terminates in a two-segmented club, lack propodeal spines, have a two-segmented waist, and have a prominent stinger. The aforementioned characteristics will serve to easily separate this genus from other genera in our region; however species level identification is difficult. In Mississippi, S. richteri is most similar to S. invicta Forel, the Red Imported Fire Ant, which is generally more red in overall color, does not have black antennal scapes, and lacks a strongly pronounced humeral area on the pronotum. These two closely related species produce a hybrid, Solenopsis invicta X richtera, which have characteristics of both.The most reliable method for identification of this group is a cuticular hydrocarbon test, which some labs are now equipped to do.

Identification 
Worker: Polymorphic, small to medium sized (TL ≈ 1.0–4.0 mm; HL 1.30–1.46 mm, HW 1.19–1.39 mm, SL 1.04–1.13 mm, EL 0.20-0.23mm, MeSL 1.52-1.65 (n=5) (MEM specimens). Head, mesosoma, waist, coxae, femora, tibia, and first tarsal segment brownish black; gaster usually darker with with a large reddish orange colored spot of the first segment of the gaster; scape blackish, funiculus and tarsi 2–5 reddish brown. Head slightly longer than wide, rounded rectangular; smooth and shining except for piligerous punctures from which light colored erect setae arise; posterior border of head flat to slightly convex in smaller workers to having strong posterior lobes and strong medial indention in larger workers; eyes small, located laterally at about the midpoint of the head; antennae 10-segmented with a 2-segmented club; clypeus tridentate with two lateral toothlike projections and one smaller toothlike projection medially; mandibles triangular with 5 prominent teeth. Mesosoma mostly smooth and shining, lacking sculpture except for transverse striae on katepisternum and lower portion of propodeum; numerous long, erect setae present; humeral pronotal process present on larger workers metanotal groove distinct and well defined; propodeum unarmed. Gaster smooth and shining with erect setae; sting present.

Queen: (Description from Buren 1972). Large, HL 1.25–1.30 mm, HW 1.35–1.40 mm, SL 1.02–1.06 mm. MeSL 2.55– 2.69 mm. Coloration similar to that of workers: Head, scapes, mesosoma, legs, and petiole brownish black; gaster nearly black, but with a bright orange spot on the anterior portion of the first gastric tergite; postpetiole or the rear portion of it usually the same color as the gastral spot. Head about as wide as long, rounded square; smooth and shining with scatterred erect setae; posterior margin median with a crease-like excision; eyes large and situated laterally at the midpoint of the head; three ocelli present; antennae 11-segmented with a 2-segmented club; scapes slightly exceed posterior margin of head; clypeus tridentate, median tooth minute, with two anteriorly diverging carinae; mandibles with 4 teeth. Mesosoma rounded rectangular, almost square, with mesoscutum rounded anteriorly; mostly mooth and shining except some striae present on anterior portion of mesoscutellum and propodeum with numerous transverse striae; numerous erect setae present dorsally and on propodeum, but sparse on pronotum and mesopleura; dorsal surface relatively flat; four wings or wing scars present; propodeum unarmed; declivity straight, almost 90°. Wings clear with light amber colored viens; forewing with costal, basal, subbasal, submarginal, and discal cells presesnt, pterostigma present; hindwing with costal, basal, and anal cells present.  Waist 2-segmented, anterior faces of petiole and postpetiole with moderately dense, appressed pubescence; erect hairs numerous and present on all surfaces; petiolar node narrower than the postpetiolar node in lateral view; sides of petiole finely punctate and roughened. Gaster shining with long erect setae; sting present.

Male: (Description from Buren 1972 and MEM specimen). Medium sized, about the size of large worker (HL 0.76–0.84 mm, HW 1.02–1.06 mm, MeSL 2.60–2.69 mm. Entire body black except funiculus, which is yellowish brown to reddish brown; wings transparent. Head small compared to the mesosoma, circular; shiny with course rugae anteriorly fading to dense punctation posteriorly, clypeus  mostly lacking sculpture; with numerous long, erect, whitesh colored setae present; eyes large, more than twice the head length, located on the anterior half of the head; three large ocelli present; frontal carina reduced; antennae 12-segmented, scape short, subequal to antennae segments 3-12; second antennal segment (pedicel) short, ovoid; clypeus without trace of carinae; mandibles small, with 2 teeth. Mesosoma bulky, elliptical in lateral view; mostly mooth and shining except some striae present on anterior portion of mesoscutellum and propodeum with dense punctation; entire mesosoma with numerous erect, elongate, whitesh setae present; propodeum unarmed. Wings clear with light amber colored viens; forewing with costal, basal, subbasal, submarginal, and discal cells presesnt, pterostigma present; hindwing with costal, basal, and anal cells present. Waist 2-segmented, both nodes with dense, fine punctation; petiolar node with a dorsal median notch. Gaster shiniy, with  numerous erect, light colored, elongate setae, especially posterially genitalia visible at the apex.

Biology
Imported black fire ants are most common in urban areas, where they nest in open, disturbed sites such as lawns, fields, and roadsides. Similar to the related S. invicta, S richteri also constructs a large, conical dirt mound above ground, which is an extensions of the remainder of the colony located below the surface. Colonies are monogynous, with only one queen, and may have up over 200,000 individuals in a large colony. Fire ants are omnivorous and eat a wide variety of foods such as arthropods, dead mammals and other animals, seeds, and numerous sweet substances including hemipteran produced honeydew. Workers typically forage during the day on warm to hot days. Pheromones and semiochemicals are used as a means of communication for defense, foraging, and recruitment. Nuptial flights occur during warm seasons.

Pest Status
The negative effects of the black imported fire ant are very similar to that of the red imported fire ant, but at a smaller scale, as this species is less common in the USA. Because fire ants thrive in urban areas, their presence can be a deterrent to outdoor activities. The fire ant sting is potent and may result in itchy red bumps that in some individuals forms hardened pustules that will eventually go away. Some victims suffer anaphylactic shock from the stings and require medical treatment. Fire ants also may inflict serious injury or even kill other animals, especially weak or sick individuals. Nests may be constructed under structures such as pavements and foundations, where they may cause structural problems. Fire ant workers have been reported to short out electrical equipment. Imported fire ants are serious agricultural pests that invade and damage a variety of crops and their mounds can damage machinery and affect harvesting.

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

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

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

Acknowledgments
Thanks to Ryan J. Whitehouse for help with measuring specimens, comments on descriptions, photography of some specimens, and proofreading. 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 (2001-2014) and USDA-ARS Areawide Management Invasive Ants 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.

Links
AntCat
AntWeb
AntWiki
Extension Fire Ant Site- http://www.extension.org/fire+ants
Texas A & M Fire Ant Site- http://fireant.tamu.edu/
Imported Fire Ants in Tennessee - http://fireants.utk.edu/
Imported Fire Ant and Household Insects (IFAHI) research site-http://www.ars.usda.gov/Main/site_main.htm?modecode=66-15-10-15
LSU red imported fire ant research- http://www.lsu.edu/ants/index.shtml
Control of the Red Imported Fire Ant -http://www.ces.ncsu.edu/depts/ent/notes/Urban/ifa.htm