Subfamily MYRMICINAE
Tribe ATTINI
Strumigenys angulata M. R. Smith 1931

by Joe A. MacGown, last updated on 19 November 2013

Strumigenys angulata, full face view of worker (click image to enlarge)
Photo by Joe MacGown
Strumigenys angulata, profile view of worker (click image to enlarge) Photo by Joe MacGown
Strumigenys angulata, full face view of worker (click image to enlarge) Photo by Joe MacGown
Strumigenys angulata, profile view of worker (click image to enlarge) Photo by Joe MacGown
Strumigenys angulata, full face view of worker (click image to enlarge) Photo by Joe MacGown and Richard Brown
Strumigenys angulata, closeup of mandibles of worker (click image to enlarge) Photo by Joe MacGown and Richard Brown
Strumigenys angulata, closeup of mandibles of worker (click image to enlarge) Photo by Joe MacGown and Richard Brown
Strumigenys angulata, spongiform tissue on waist of worker (click image to enlarge) Photo by Joe 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 whereat 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 bimarginata is a rarely collected species in the clypeata group.

Taxonomic History (provided by Barry Bolton, 2013)
Described as Strumigenys (Cephaloxys) angulata by  Smith (1931); Combination in Strumigenys (Trichoscapa): Smith, 1947; Creighton, 1950; in Smithistruma (Wessonistruma): Brown, 1948; Brown, 1953; in Pyramica: Bolton, 1999; in Strumigenys: Baroni Urbani & De Andrade, 2007.

Identification.
TL 2.2–2.3, HL 0.56–0.60, HW 0.42–0.43, CI 73–79, ML 0.16–0.19, SL 0.28–0.31, PW 0.23–0.25, WL 0.58–0.64 (measurements and description from Bolton (2000)). Mandibles elongate and sublinear, basal lamella short, triangular, dentition restricted to apical third of mandible with basl and next three teeth triangular and acute, second tooth longer than the basal tooth. Clypeus with anteriolateral angles angular in full-face view, lacking peripheral groove. Propodeum with triangular teeth with lamella. Spongiform appendages well developed on dorsum and ventral portions of petiole and postpetiole; first gastral tergite with narrow band of weak spongiform tissue present basally. Clypeus in full-face view with long, translucent spatulate setae all directed anteriorly or weakly toward midline of head; clypeal dorsum with numerous reclinate, translucent, spatulate setae directed anteriorly away from the midline, setae shorter than those on fringe; remainder of cephalic dorsum with less dense, similarly shaped, but larger, more flattened setae directed anteriorly or slightly toward the midline of head; pronotal and mesonotal dorsum with scattered semi-erect, spatulate setae directed posteriorly. Scape with spatulate to spoon-shaped setae, some of which curve toward scape base. Dorsum of head lacking long erect setae. Pronotal humeral setae usually lack long setae, one pair of simple erect setae present on mesonotal dorsum, and scattered erect simple setae present on dorsum of petiole, postpetiole, and gaster. Clypeal dorsum and dorsum of head behind clypeus reticulate-punctate; pleurae, side of propodeum, and postpetiole disc smooth, remainder of mesosoma and petiole disc with reticulate-punctate sculpture; first gastral tergite with striae basally, then becoming smooth.

This species can really only be confused with one other species, S. pergandei, S. angulata differs by having the anterior and lateral margins of the clypeus meeting in angular corners (see full face photo above), rather than rounded curves (as in S. pergandei); the second tooth on the mandible is longer than the basal tooth, whereas, in S. pergandei, the basal tooth is longer than the second or third tooth; the postpetiolar disc lacks posteriorly curved spatulate hairs (present in S. pergandei); and the mesonotal dorsum has a pair of erect simple hairs (lacking in S. pergandei).

Biology and Economic Importance
Strumigenys angulata is a rarely collected species of Strumigenys in many parts of the country, but in AL and MS, it seems to be relatively common and has been collected somewhat regularly in soil and litter in mixed and deciduous forests. We have found this species to be especially common in soil and litter at bases of hardwood trees in upland hardwood forests. Due to its minute size, cryptic habits, and rarity of collection, this species would pose no discernible affects upon man.

Distribution
Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Missouri, North Carolina, South Carolina, and Tennessee (MEM records; Bolton 2000).

Literature Cited

Baroni Urbani, C.; and De Andrade, M. L. 2007. The ant tribe Dacetini: limits and constituent genera, with descriptions of new species (Hymenoptera, Formicidae). Annali del Museo Civico di Storia Naturale "Giacomo Doria" 99:1-191. 

Bolton, B.  1999.  Ant genera of the tribe Dacetonini (Hymenoptera: Formicidae).  Jour. Nat. Hist. 33: 1639-1689. 

Bolton, B. 2000.  The ant tribe Dacetini.  Mem. American Entomol. Inst. 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. 1948. A preliminary generic revision of the higher Dacetini (Hymenoptera: Formicidae). Trans. Am. Entomol. Soc. 74: 101-129.

Brown, W. L., Jr. 1953. Revisionary studies in the ant tribe Dacetini. Am. Midl. Nat. 50: 1-137

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

Smith, M. R. 1931c. A revision of the genus Strumigenys of America, north of Mexico, based on a study of the workers (Hymn.: Formicidae). Annals of the Entomological Society of America 24:686-710.

Smith, M. R. 1947. A generic and subgeneric synopsis of the United States ants, based on the workers. American Midland Naturalist 37: 521-647.

Smith, M. R. 1951. Family Formicidae. Pp. 778-875 in: Muesebeck, C. F.; Krombein, K. V.; Townes, H. K. (eds.) 1951. Hymenoptera of America north of Mexico. Synoptic catalogue. United States Department of Agriculture. Agriculture Monograph 2: 1-1420.

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