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Subfamily MYRMICINAE
Tribe ATTINI

Cyphomyrmex rimosus (Spinola) 1851

rimose fungus ant

Author: Joe A. MacGown
Uploaded, 2009; last updated 31 March 2016

Cyphomyrmex rimosus, full face view of the head of a worker (MS, Harrison Co.) (photo by Joe A. MacGown)
Cyphomyrmex rimosus, lateral view of a worker (MS, Harrison Co.) (photo by Joe A. Macgown)
Cyphomyrmex rimosus, dorsal view of gaster of a worker (MS, Harrison Co.) (photo by Joe A. Macgown)
Cyphomyrmex rimosus, full face view of the head of a worker (MS, Harrison Co.) (photo by Joe A. MacGown)
Cyphomyrmex rimosus, lateral view of a worker (MS, Harrison Co.) (photo by Joe A. Macgown)
Cyphomyrmex rimosus, dorsal view of a worker (MS, Harrison Co.) (photo by Joe A. Macgown)
Cyphomyrmex rimosus, full face view of the head of a queen (MS, Pearl River Co.) (photo by Joe A. MacGown)
Cyphomyrmex rimosus, lateral view of the head of a queen (MS, Pearl River Co.) (photo by Joe A. MacGown)
Cyphomyrmex rimosus, dorsal view of the head of a queen (MS, Pearl River Co.) (photo by Joe A. MacGown)
Cyphomyrmex rimosus, full face view of the head of a male (MS, Lincoln Co.) (photo by Joe A. MacGown)
Cyphomyrmex rimosus, lateral view of the head of a male (MS, Lincoln Co.) (photo by Joe A. MacGown)
Cyphomyrmex rimosus, dorsal view of the head of a male (MS, Lincoln Co.) (photo by Ryan Whitehouse and Joe A. MacGown)
Cyphomyrmex rimosus, workers with brood (Photo by Stoy Hedges)
Cyphomyrmex rimosus, workers with brood (Photo by Stoy Hedges)

Introduction
Cyphomyrmex is a genus in the tribe Attini and is related to the Atta and Trachymyrmex genera. Cyphomyrmex species can be found across the Neotropical region. and into the southern Nearctic region. These ants cultivate fungal gardens, from which they use the mycelium and yeast as a food source, but they do not cut leaves. This genus is divided into two groups based on what they cultivate with one cultivating fungus and the other cultivating fungus and yeast.

Cyphomyrmex species can be identified by their greatly enlarged frontal lobes, 11-segmented antennal with a two-segmented club, triangular mandibles with five teeth, and blunt tubercles on the dorsum of the mesosoma.

Cyphomyrmex rimosus is a small dull brown to blackish brown Attine ant with deep antennal scrobes, enlarged frontal lobes that obscure the lateral margins of the face, no propodeal spines, an apendiculate petiole, and tubercles on the mesosoma. The species is native to the Neoptropics, but has become established in the southern United States and the Galapagos Islands. C. rimosus is not considered a pest species in its native range.

Taxonomic History (Bolton, 2013)
Cryptocerus rimosus Spinola (1851); also described as new by Spinola (1853); Combination in Cyphomyrmex, Emery (1893); in Atta (Cyphomyrmex), Forel (1912); in Cyphomyrmex, Bruch (1914). Senior synonym of Cyphomyrmex difformis, Forel (1893); Emery (1894); of Cyphomyrmex cochunaeCyphomyrmex fuscus (and its junior synonyms Cyphomyrmex curidpensis, Cyphomyrmex fuscula), Snelling and Longino (1992).

Identification
Worker: HL 0.83-0.86mm, HW 0.73-0.75mm, SL 0.71-0.76mm, EL 0.18-0.19mm, MeSL 1.09-1.13mm (n=5) (MEM specimens). Workers are monomophic; color various from dull light brown to blackish brown to bicolored with, head and gaster dark brown to blackish and mesosome reddish borwn, with legs and antennal funiculi sometimes a lighter orangish brown. Head opaque in appearance with fine granulate sculpture, entire surface often dulled with a whitish cast; numerous appressed scale-like setae present on head including clypeus; eyes well developed and situated laterally below the antennal scrobes; mandibles triangular with five teeth; antennae 11-segmented with two-segmented club; second segment of the antennal club more than twice as long as the first segment; frontal lobes conspicuously expanded laterally, covering the antennal insertion point as well as much of the head giving the face a notched appearance. Mesosoma matte in appearance; with sparse scale-like setae, more numerous on dorsum; prominent rounded tubercles present on the dorsum; propodeum lacking obvious spines. Waist two-segmented; matte in appearance, with scattered scale-like setae present; petiole triangular-trapezoidal in lateral view; postpetiole enlarged, with a shallow, medial glabrous depression on the dorsal surface. Gaster with similar matte appearance as head and mesosoma, with fine granulation; numerous short, appressed, scale-like setae present; anterior edge of first tergite with glabrous, medial depression; first tergite enlarged to make up a majority of the gaster’s size; sting present. 

Queen: HL 0.86-0.89mm, HW 0.78-0.81mm, SL 0.72-0.75mm, EL 0.22-0.23mm, MeSl 1.20-1.27mm (n=5) (MEM specimens). Entire body except appendages overall, dull light brown to blackish brown in color. or dusky gray with legs and antennae usually orangish brown. Head with fine granulate sculpture giving it a matte appearance; with scale-like setae; eyes well developed and located below the antennal scrobes; small ocelli located on three tubercles placed dorsoposteriorly; mandibles triangular in shape with five teeth; lateral portions of clypeus raised and directed anteriorly; antennae 11-segmented with a two-segmented club; antennal insertion point hidden by largely expanded frontal lobes that give the face a notched look. Mesosoma with fine granulate sculpture, matte in appearance; dense, short, appressed, scale-like setae present on dorsum, mostly lacking on pronotum, mesopleuron, and metapleuron; pronotum with two humeral tubercles that project dorsoanteriorly; metanotum notched posteriorly and overhanging propodeum; propodeum lacking spines. Wings, when present, dusky grayish brown; forewing with costal, basal, subasal, submarginal, and marginal cell; medial vein extending to wing tip; pterostigma absent; hind venation simple with only the submarginal cell closed. Waist two-segmented, opaque, with appressed scale-like setae; petiole triangular-trapezoidal; postpetiolar node enlarged, in dorsal view hemispherical, with a shallow, medial depression on the dorsal surface; posterior margin of postpetiole with wide notch. Gaster opaque, with numerous appressed, scale-like setae; distinct, medial, glabrous depression present anterodorsally that lines up with postpetiolar medial depression; first tergite enlarged making up majority of the gaster’s size; sting present.

Male: HL 0.66-0.70mm, HW 0.58-0.61mm, SL 0.81-0.84mm, EL 0.26-0.28mm, MeSL 1.20-1.27mm n=5) (MEM specimens). Color overall dark brown to brownish black, legs dark orangish brown. Head with fine punctation, matte, with scattered, short, appressed, setae; eyes large and distinctly convex; three ocelli present on blunt tubercles; mandibles triangular; lateral edges of clypeus slightly raised; antennae 13-segmented; scape elongate, about as long as head length; last funicular segment elongated and more than twice the length of the preceding segment; frontal processes enlarged and distinctly projecting anteriorly; posterior edge of head flat with triangular tubercle at each posterior corner. Mesosoma with roughened, matte apperance, with hair-like setae dorsally; two tubercles on the pronotum; posterior edge of metanotum notched; propodeal spines lacking. Wings grayish brown; forewing with costal, basal, subasal, submarginal, and marginal cell; medial vein extending to wing tip; pterostigma absent; hind venation simple with only the submarginal cell closed. Waist two-segmented; both nodes matte, with fine granulate sculpture; scattered, short appressed, thickened setae present; petiole with short anterior peduncle, node smoothly arched anteriorly and slightly raised posteriorly in profile view; postpetiolar node enlarged with a shallow, medial, glabrous depression. Gaster with small, hair-like setae; faint, almost imperceptible anterior medial depression aligned with the postpetiolar depression, sometimes only visible as a flat area instead of being convex like the rest of the gaster; first tergite enlarged to make up a majority of the gaster’s size; genitalia present at the apex with large parameres obvious.

This species is similar to Cyphomyrmex minutus, which is apparently native to Florida and smaller in size. According to Snelling and Longino (1992), the head width of C. minutus is less than 0.56mm and the setae in the center of the first gastral tergite are closely appressed and usually separated by more than their own lengths, whereas in C. rimosus, the head width is greater than 0.62mm and the hairs on the first gastral tergite are not completely appressed and are separated by less than their own lengths. Specimens of both species were examined by Joe MacGown at the collection in Gainesville, Florida. MacGown had a hard time telling them apart, but he did not have an ocular micrometer to measure head widths with.

Biology and Economic Importance
Cyphomyrmex rimosus is part of a complex of closely related and highly variable taxa that can be difficult to distinguish (Kempf, 1996 (1965)). The C. rimosus group was split into five subgroups by Snelling and Longino (1992) and now contains seven species including C. rimosus and the closely related C. minutus. Both of these species occur in Florida. However, based on its rapid spread after initially being detected, C. rimosus is thought to be introduced; whereas, C. minutus is considered native (Deyrup, 1991). Prior to the revision by Snelling and Longino (1992), C. minutus was treated as a junior synonym of C. rimosus. This synonymization makes it difficult to know exactly which species earlier studies referred to. Snelling and Longino (1992) state the many of the Neotropical and Nearctic records in the literature may actually refer to the more widespread C. minnutus.

The colony size of C. rimosus is typically small, with usually less than 100 workers, although colonies with over 300 workers have been observed (Murakami & Higashi, 1997). Colonies are typically monogynous, but may be polygynous (Murakami & Higashi, 1997; Snelling and Longino, 1992).

Similar to other Attines, Cyphomyrmex cultivates subterranean fungus gardens, growing the fungus on a substrate of vegetable matter, insect frass, and dead insects. These fungus gardens are composed of yeasts in the unicellular phase. Fungal gardens of most other Attine species are in the multicellular, mycelial phase (Mehdiabadi & Schultz, 2010). C. rimosus supplements its diet with nectar and the sap of plants (Murakami & Higashi, 1997). The queens have been reported to practice monandry and semi-claustral nest founding (Mehdiabadi & Schultz, 2010; Tschinkel, 1987). Nests are often simple, shallow, impermanent structures under rocks, logs, dry cow manure, or any other surface. The species is very common in open habitats such as pastures and also in open woodlands such as longleaf pine forests.

This species in not considered to be a pest, but in areas of high abundance, they could invade homes in search of sugary food substances.

Distribution
Native Range: South America (antweb.org).

Nearctic Region: United States (antweb.org and antwiki.org).
Neotropical Region:  Argentina, Belize, Bolivia, Brazil (type locality), Colombia, Costa Rica, Dominican Republic, Ecuador, French Guiana, Galapagos Islands, Greater Antilles, Guatemala, Guyana, Haiti, Lesser Antilles, Martinique, Mexico, Nicaragua, Panama, Paraguay, Peru, Suriname, Trinidad and Tobago, Uruguay, Venezuela (antweb.org and antwiki.org).

U.S. Distribution: AL, FL, GA, LA, MS, NM, SC, TX (antweb.org and MEM).
Southeastern U.S. Distribution: AL, FL, GA, LA, MS, SC (antweb.org and MEM).

Acknowledgments
Thanks to Ryan J. Whitehouse for help with measuring specimens and proofreading. Thanks to Stoy Hedges for permission to use his images here. 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
Bolton, B. 2013.  Bolton World Catalog Ants. Available online: http://www.antweb.org/world.jsp. Accessed 16 April 2013.

Bruch, C. 1914. Catálogo sistemático de los formícidos argentinos. Revista del Museo de La Plata 19: 211-234.

Deyrup, M. 1991. Exotic ants of the Florida keys (Hymenoptera: Formicidae). In: Eshbaugh, W.H. (Ed.) Proceedings of the 4th symposium on the natural history of the Bahamas. Bahamian Field Station, San Salvador, Bahamas, pp. 15-22.

Emery, C. 1893. Intorno ad alcune formiche della collezione Spinola. Bollettino dei Musei di Zoologia ed Anatomia Comparata della Reale Università di Torino 8(163): 1-3. 

Emery, C. 1894. Studi sulle formiche della fauna neotropica. VI-XVI. Bullettino della Società Entomologica Italiana 26: 137-241. 

Forel, A. 1893. Note sur les Attini. Annales de la Société Entomologique de Belgique 37: 586-607. 

Forel, A. 1912. Formicides néotropiques. Part II. 3me sous-famille Myrmicinae Lep. (Attini, Dacetii, Cryptocerini). Mémoires de la Société Entomologique de Belgique 19: 179-209.

Mehdiabadi, N. J. and R. Schultz. 2010. Natural history and phylogeny of the fungus-farming ants (Hymenoptera: Formicidae: Myrmicinae: Attini). Myrmecol. News, 13: 37-55.

Murakami, T. and S. Higashi. 1997. Social organization in two primitive attine ants, Cyphomyrmex rimosus and Myrmicocrypta ednaella, with reference to their fungus substrates and food sources. J. Ethol., 15, 17-25.

Kempf, W.W. (1966 (1965)) A revision of the Neotropical fungus-growing ants of the genus Cyphomyrmex Mayr. Part II: Group ofrimosus (Spinola) (Hym., Formicidae). Stud. Entomol., 8: 161-200.

Smith, D. R. 1979. In Catalog of Hymenoptera in America north of Mexico. Smithsonian Institution Press, Washington D. C. Vol. 2, pp. 1323-1427.

Snelling, R. R. and J. T. Longino. 1992. Revisionary notes on the fungus-growing ants of the genus Cyphomyrmexrimosus-group (Hymenoptera: Formicidae: Attini). Pages 479-494 in Quintero, D. and A. Aiello. Insects of Panama and Mesoamerica: selected studies. Oxford University Press, Oxford. 692 pp.

Spinola, M. 1851. Compte rendu des Hyménoptères inédits provenants du voyage entomologique de M. Ghiliani dans le Para en 1846. Extrait des Mémoires de l'Académie des Sciences de Turin (2)13: 3-78.

Spinola, M. 1853. Compte rendu des Hyménoptères inédits provenants du voyage entomologique de M. Ghiliani dans le Para en 1846. Memorie della Reale Accademia delle Scienze di Torino (2)13: 19-94. 

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