Subfamily MYRMICINAE
Tribe ATTINI
Strumigenys silvestrii Emery, 1906

Authors: Joe A. MacGown and Ryan J. Whitehouse
Uploaded, 2009; last updated 30 August 2016

Strumigenys  silvestrii, full face view of worker (MS, George Co.) (photo by Ryan Whitehouse and Joe A. MacGown)

Strumigenys  silvestrii, lateral view of worker (MS, George Co.) (photo by Ryan Whitehouse and Joe A. MacGown)

Strumigenys  silvestrii,dorsal view of worker (MS, George Co.) (photo by Ryan Whitehouse and Joe A. MacGown)

Strumigenys  silvestrii, full face view of alate queen (MS, Clarke Co.) (photo by Ryan Whitehouse and Joe A. MacGown)

Strumigenys  silvestrii, lateral view of alate queen (MS, Clarke Co.) (photo by Ryan Whitehouse and Joe A. MacGown)

Strumigenys  silvestrii, dorsal view of alate queen (MS, Clarke Co.) (photo by Ryan Whitehouse and Joe A. MacGown)

Strumigenys  silvestrii, lateral view of alate queen (MS, Clarke Co.) (photo by Ryan Whitehouse and Joe A. MacGown)

Strumigenys  silvestrii, lateral view of mesosoma of worker (MS) (SEM photo by Joe A. MacGown and Richard Brown)

Strumigenys  silvestrii, close up view of a seta found on gastral dorsum of worker (MS) (SEM photo by Joe A. MacGown and Richard Brown)

Strumigenys  silvestrii, full face view of worker (MS) (SEM photo by Joe A. MacGown and Richard Brown)

Strumigenys  silvestrii, mandibles of worker (MS) (SEM photo by Joe A. MacGown and Richard Brown)

Strumigenys  silvestrii, clypeal area of worker(MS) (SEM photo by Joe A. MacGown and Richard Brown)

Introduction
Strumigenys is a monophyletic genus of dacetine ants that includes over 900 species worldwide (Bolton 2013). Forty-eight described species of Strumigenys have been reported from the US (Bolton 2013), but this genus is most speciose in the Southeast where at least 43 species are known to occur.

In the US, members of the genus Strumigenys can easily be distinguished from other genera by their minute size; 4-6 segmented antennae; elongate, snapping mandibles; unique and often "bizarre" pilosity, and presence of "spongiform lobes" beneath the petiole and postpetiole (Bolton 1999). Dacetines are predatory ants that generally feed on tiny soil arthropods (Wilson 1953).  Most dacetines are small, cryptically colored, rarely forage openly above ground, are slow moving, and become motionless when disturbed.

Strumigenys silvestrii is a tiny predatory ant species native to South America. In recent years, this species has become established in the US, especially in the southeastern region where it has been collected in a variety of habitats. Strumigenys silvestrii workers and queens possess extremely elongate mandibles and antennae.

Taxonomic History
Strumigenys silvestrii Emery, 1906: 168, fig. 27 (w.q.) ARGENTINA. Neotropic.
Senior synonym of Strumigenys caribbea: Brown, 1959}: 25. See also: Bolton, 2000: 559.

Diagnosis
Strumigenys silvestrii workers can be recognized by their minute size, reddish brown color, narrowed heart-shaped head, elongate six-segmented antennae terminates in a two-segmented club, elongate mandibles with three apical teeth and often a small denticle on the inside of mandible about midway, and petiole lacking a spongiform curtain. In the US, this species is most similar to the native S. louisianae, from which it differs by being smaller, having a narrower head, and often having a denticle along the inner margin of the mandible about midway.

Identification
Worker:Minute, HL 0.44–0.46 mm, HW 0.34-0.36mm, SL 0.30-0.32mm, EL 0.02-0.03mm, MeSL 0.44-0.47mm (n=5) (MEM specimens). Entire body reddish brown. Head heart-shaped, widest posteriorly, deeply concave along posterior border; antennal scrobes present on lateral sides of head; entire head with tightly woven foveolate reticulation; clavate scale-like setae numerous on face and margin of head, all setae directed anteriorly; eyes small with only a few facets, located laterally below the antennae; mandibles narrowed and elognate, approximately half the length of the head, with three distinct apical teeth and with a small denticle located along the inner margin of the mandible at about the midpoint; antennae 6-segmented, scape nearly reaching occipital border, most of the setae along the inner margin of the scape directed toward scape apex except for at least two setae directed toward scape base, apical flagellomere greatly enlarged, and subequal in length to scape. Mesosoma with dense, tightly woven foveolate reticulate sculpture; scattered erect, scale-like setae present dorsally; dorsal surface of mesosoma forming a continuous arc in lateral view; promesonotal suture forming a distinct carinae; propodeum with small triangular spines. Waist 2-segmented, with scattered erect, clavate setae directed posteriorly; petiole with tightly woven foveleolate sculpture, peduncle thickened in lateral view, spongiform tissue lacking ventrally, node somewhat rectangular in dorsal view; postpetiole shiny, with spongiform tissue present ventrally and posteriorly, in dorsal view node kidney bean shaped and about twice as wide as petiole. Gaster smooth, shiny, with longitudinal grooves present on anterior portion of first tergite; scattered erect, clavate setae present; sting present.

Queen:Minute (HL 0.48 mm, HW 0.38 mm, SL 0.30 mm, EL 0.07 mm, MeSL 0.52 mm) (n=1) (MEM specimen). Minute brown ant, slightly darker than the workers and slightly longer. Entire body reddish brown. Head heart-shaped, widest posteriorly, deeply concave along posterior border; antennal scrobes present on lateral sides of head; entire head with tightly woven foveolate reticulation; clavate scale-like setae numerous on face and margin of head, all setae directed anteriorly; eyes large, located on the ventral side of the antennal scrobe; three ocelli present, often with black coloration around them; mandibles elongate, approximately half the length of the head, with a distinct apical fork followed by a single tooth, with a small denticle located along the inner margin of the mandible at about the midpoint; antennae 6-segmented, scape nearly reaching occipital border, most of the setae along the inner margin of the scape directed toward scape apex except for at least two setae directed toward scape base, apical flagellomere greatly enlarged, and subequal in length to scape. Mesosoma squarish in lateral view,  densely foveolate with the meso- and metaplural region smooth; scattered erect, scale-like setae present dorsally; propodeum with two posteriorly directed triangular teeth present. Wings, if present, lacking pigmented veins, stigma absent, with fringe of setae along wing edges apically and on ventral sides of wings to about midway toward base. Waist 2-segmented, with scattered erect, clavate setae directed posteriorly; petiole with tightly woven foveleolate sculpture, peduncle thickened in lateral view, spongiform tissue lacking ventrally, node somewhat rectangular in dorsal view; postpetiole shiny, with spongiform tissue present ventrally and posteriorly, in dorsal view node kidney bean shaped and about twice as wide as petiole. Gaster smooth, shiny, with longitudinal grooves present on anterior portion of first tergite; scattered erect, clavate setae present; sting present.

Biology
Strumigenys silvestrii has been found in leaf litter in coastal hardwood forests, bottomland hardwood forests, the Black Belt Prairie, and vacant urban lots. Ants in this genus tend to be slow moving and very cryptic, often halting all movement when disturbed, as well as rarely venturing into the open. Strumigenys silvestrii most likely feeds on Collembola and other small soil arthropods with their trap-jaw mandibles, like other species in this genus with similar mandibles.

Pest Status
It is not considered to be a pest or a nuisance since and is rarely encountered by the average person. Its affect, if any, on other native Strumigenys species in the region have not been studied.

Distribution
Native Range: South America (AntWiki.org and MEM).

Nearctic: United States (AntWiki.org, MEM).
Neotropical: Argentina, Bahamas, Brazil, Cuba, Dominican Republic, Greater Antilles, Mexico, Paraguay (AntWeb.org and AntWiki.org).
Palearctic: China, Iberian Peninsula, Macaronesia, Portugal (AntWeb.org and AntWiki.org).

U.S. Distribution: AL, CA, FL, GA, LA, MS, TX (AntWiki.org and MEM).
Southeastern U.S. Distribution: AL, FL, GA, LA, MS (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
Bolton, B.  1999.  Ant genera of the tribe Dacetonini (Hymenoptera: Formicidae).  Journal of Natural History 33: 1639-1689.

Bolton, B. 2000. The ant tribe Dacetini. Memoirs of the American Entomological Institute 65:1-1028.

Bolton, B. 2013.  Bolton World Catalog Ants. Available online: http://www.antweb.org/world.jsp. Accessed 16 April 2013.

Brown, W. L., Jr. 1959. The Neotropical species of the ant genus Strumigenys Fr. Smith: group of silvestrii Emery. Studia Entomologica (n.s.) 2:25-30.

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

Wilson, E. O. 1953. The ecology of some North American dacetine ants. Annals of the Entomological Society of America 46: 479-497.

Links

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AntCat
AntWiki