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Subfamily ECTATOMMINAE
Tribe ECTATOMMINI

Gnamptogenys triangularis (Mayr, 1887)

South American grooved ant

Authors: Joe A. MacGown and Ryan J. Whitehouse
Uploaded 2009; updated 23 August 2016

Gnamptogenys triangularis, full face view of a worker (MS, Harrison Co.) (photo by Joe A. MacGown)
Gnamptogenys triangularis, lateral view of a worker (MS, Harrison Co.) (photo by Joe A. MacGown)
Gnamptogenys triangularis, dorsal view of a worker (MS, Harrison Co.) (photo by Joe A. MacGown)
Gnamptogenys triangularis, full face view of a queen (MS, Pearl River Co.) (photo by Ryan Whitehouse and Joe A. MacGown)
Gnamptogenys triangularis, lateral view of a queen (MS, Pearl Rive Co.) (photo by Ryan Whitehouse and Joe A. MacGown)
Gnamptogenys triangularis, dorsal view of a queen (MS, Pearl Rive Co.) (photo by Ryan Whitehouse and Joe A. MacGown)
Gnamptogenys triangularis, full face view of a male (MS, Pearl River Co.) (photo by Ryan Whitehouse and Joe A. MacGown)
Gnamptogenys triangularis, lateral view of a male (MS, Pearl Rive Co.) (photo by Ryan Whitehouse and Joe A. MacGown)
Gnamptogenys triangularis, dorsal view of a male (MS, Pearl Rive Co.) (photo by Ryan Whitehouse and Joe A. MacGown)

Gnamptogenys triangularis, full face view of a worker

Gnamptogenys triangularis, lateral view of a worker


Gnamptogenys triagularis male full face view
Gnamptogenys triangularis, full face view of a male (photo by Joe A. MacGown)
Gnamptogenys triangularis, lateral view of a male (photo by Joe A. MacGown)
Gnamptogenys triangularis, lateral view of a male (photo by Joe A. MacGown)

Introduction
Gnamptogenys is a genus comprising of more than 130 species that are primarily predaceous. Most species in this genus are found in tropical areas of Southeast Asia and Australia, but they can also be found in tropical South and Central America. Colonies tend to be found in rotten wood and leaf litter and rarely exceed a few hundred individuals. While most species have a reproducing queen, a few species of Gnamptogenys have workers that reproduce instead of queens (Gobin et al. 2001). Gnamptogenys triangularis and G. hartmanni are the only two members of the subfamily Ectatomminae known to occur in the southeastern US. These very distinctive ants can be recognized immediately by their relatively large size (3.5-5.0 mm in total length), the deep horizontal grooves covering the entire body, and single petiolar node.

Gnamptogenys triangularis can be found along the gulf states and was first reported in Florida was collected in 1985 (Deyrup et al. 2000). At the moment it is considered to be rare and to have negligible affects on the environment (Deyrup et al. 2000). It has also been reported to be a millipede specialist (Deyrup et al. 2000, Lattke 1995).

Taxonomic History (Bolton 2016)
Ectatomma triangulare Mayr, 1887: 544 (q.) URUGUAY. Neotropic.
Emery, 1906: 113 (w.). Combination in Gnamptogenys (Parectatomma): Emery, 1911: 44; in Gnamptogenys: Brown, 1958}: 230. Senior synonym of Gnamptogenys richteri: Brown, 1958g}: 230; of Gnamptogenys aculeaticoxae:Lattke, 1995: 190.

Identification
Worker: HL 1.13-1.18mm, HW 1.07-1.13mm, SL 1.07-1.10mm, EL 0.26-0.27mm, MeSL 1.67-1.74mm (n=5) (MEM specimens). Medium sized (about 5.00mm in total length) ants with dark reddish-brown head, mesosoma, and gaster with brown legs and antennae. Head, mesosoma, and gaster have distinct, shining, longitudinal grooves. Head with longer, erect setae; eyes located laterally along the midline of the head; long, triangular mandibles with a smooth to minutely serrated inner margin; antennal insertion points well separated without well developed frontal lobes; 12-segemented antennae; scape just exceeding the occipital border. Mesosoma with numerous erect setae; mesonotal suture distinct; propodeal spines minute; metacoxal spine distinct and well developed. Waist is single-segmented with distinct, shining ridges on the node; anteriorly directed subpetiolar process present on the ventral anterior side of the petiole. Gaster with numerous erect setae; first two segments elongated to make up most of the gaster; suture between the first two segments distinct and slightly depressed; anteriorly projecting ridge on the ventral anterior side of the first segment; sting present at apex.

Queen: HL 1.18-1.24mm, HW 1.18-1.22mm, SL 1.06-1.13mm, EL 0.31-0.32mm, MeSL 1.86-2.01mm (n=5) (MEM specimens). Dark brown to black ant with lighter brown legs. Head, mesosoma and gaster with distinct, longitudinal grooves. Head with conspicuous, erect setae; eyes situated laterally at about the midpoint of the head; three ocelli present; mandibles are well developed, triangular and are edentate to having minute dentition; mandibles with a slight ventral curve; distinct frontal lobes present; antennae are 12-segmented with the scape just exceeding the occipital border. Mesosoma with erect setae; enlarged with four wings or wing scars present; metacoxal spine distinct, but not always as well developed as in the workers; propodeal spines minute. Waist is one-segmented; leading edge with two dorsally located processes; anteriorly directed subpetiolar process present on the ventral side of the petiole. Gaster with numerous, erect setae; first two segments larger than the following segments with a distinct constriction at their suture; anteriorly projecting ridge on the ventral anterior side of the first segment; well develop sting present.

Male: HL 0.97-1.01mm, HW 0.91-0.98mm, SL 0.23-0.27mm, EL 0.42-0.46mm, MeSL 1.84-1.93mm (n=5) (MEM specimens). Head and mesosoma dark brown to black with a light brown to reddish-brown gaster. the legs, mandibles, and antennal scapes are a light brown and lighter than the gaster in most specimens. Head rugose with numerous long, erect setae; oval shaped eyes well developed and situated at the midpoint of the head; three slightly protruding ocelli present; mandibles well developed, triangular, and overlapping with minute serration along the inner margin; frontal lobes reduced to form a cup-like antennal insertion points; antennae 13-segmented with the second segment about as wide as it is long; scape is short. Mesosoma lacking a uniform sculpturing with some smooth, shinning spots; first abdominal segment tends to become slightly rugose; numerous erect setae present; enlarged with four wings; metacoxal spine reduce to absent. Waist is one-segmented and rugose; node is domed and subquadrate when viewed dorsally; ventrally directed subpetiolar tooth present; leading edge with two dorsally located processes. Gaster with dense, erect setae; first two segments enlarged with a distinct constriction between them; anteriorly projecting ridge present on the ventral anterior side of the first segment.

Gnamptogenys triangularis can be separated from similar ants in the area by the presence of a one-segmented waist, presence of frontal lobes and sting, and the distinct grooves and ridges that run along the body. The only other species in this genus in the southeast is G. hartmanni, which is smaller (only 3.5-4.0mm in total length), a pale reddish brown color, and lacks small propodeal teeth. The waist and gaster of G. triangularis males, workers, and queens are remarkably similar as well.

Biology and Economic Importance
This species is reported to be a predator of millipedes and a nest has been rported aas having millipede fragments in it in Florida (Deyrup et al. 2000, Lattke 1995). A small colony was found by Lloyd Davis in forested habitat in Harrison Co., MS in June in a small rotting branch on the ground. We have collected males and females in malaise traps in several counties in southern MS from mid May through mid July, and David Cross collected a male on 12 November 2010 in Forrest County, MS. 

At the moment G. triangularis is not considered to be an exotic pest. Though it can be found in Florida, Alabama and Mississippi, it is not yet common so its impact is so far largely unknown.

Distribution
Native Range: Neotropics, Costa Rica to Argentina (Lattke et al. 2007).

Nearctic: United States (antwiki.org).
Neotropical: Argentina, Bolivia, Brazil, Colombia, Costa Rica, Ecuador, French Guiana, Panama, Peru, Uruguay, Venezuela (antweb.org, antwiki.org, Longino 1998).

U.S. Distribution: AL, FL, MS (Deyrup 2003, MEM).
Southeastern U.S. Distribution: AL, FL, MS (Deyrup 2003, MEM).

Acknowledgments
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. 2016.  Bolton World Catalog Ants. Available online: http://www.antweb.org/world.jsp. Accessed 9 March 2016.

Brown, W. L., Jr. 1958. Contributions toward a reclassification of the Formicidae. II. Tribe Ectatommini (Hymenoptera). Bulletin of the Museum of Comparative Zoology 118:173-362. 

Deyrup, M. 2003. An updated list of Florida ants (Hymenoptera: Formicidae). Florida Entomologist 86: 43-48. 

Deyrup, M., L. Davis, & S. Cover. 2000. Exotic ants in Florida. Transactions of the American Entomological Society 126:293-326.

Emery, C. 1906 ("1905"). Studi sulle formiche della fauna neotropica. XXVI. Bullettino della Società Entomologica Italiana 37:107-194.

Emery, C. 1911. Hymenoptera. Fam. Formicidae. Subfam. Ponerinae. Genera Insectorum 118:1-125.

Gobin, B., J. Billen & C. Peeters. 2001. Dominance interactions regulate worker mating in polygynous Ponerine ant Gnamptogenys menadensis. Ethology 107:495-508.

Lattke, J. E. 1995. Revision of the ant genus Gnamptogenys in the New World (Hymenoptera: Formicidae). Journal of Hymenoptera Research 4:137-193.

Lattke, J.E., F. Fernández & G. Palacio, E.E. 2007. Identification of the species of Gnamptogenys Roger in the Americas. In: Snelling, R.R, B.L. Fisher & P.S. Ward (Eds.) Advances in ant systematics (Hymenoptera: Formicidae): homage to E.O. Wilson – 50 years of contributions. Memoirs of the American Entomological Institute vol. 80, Gainesville, FL, 690 p., pp. 254-270.

Longino, J. T. 1998. Gnamptogenys triangularis (Mayr 1887). http://academic.evergreen.edu/projects/ants/Genera/Gnamptogenys/SPECIES/triangularis/triangularis.html. Accessed 15 January 2009.

Mayr, G. 1887. Südamerikanische Formiciden. Verhandlungen der Kaiserlich-Königlichen Zoologisch-Botanischen Gesellschaft in Wien 37:511-632.

Links
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