Subfamily MYRMICINAE
Tribe DACETINI

Strumigenys margaritae Forel 1893

by Joe A. MacGown, last updated 4 September 2014

Strumigenys margaritae, full face view of worker
Strumigenys margaritae, profile view of worker
Strumigenys margaritae, full face view of worker (photo by Joe A. MacGown)
Strumigenys margaritae, profile view of worker (photo by Joe A. MacGown)
Strumigenys margaritae, closeup view of scape showing shape and orientation of setae (photo by Paul Davison)
Strumigenys margaritae, profile view of mesosoma, note the strong sculpture (photo by Joe A. MacGown)
Strumigenys margaritae, full face view of queen
Strumigenys margaritae, profile view of queen
Strumigenys margaritae, full face view of queen (photo by Joe A. MacGown)
Strumigenys margaritae, profile view of queen (photo by Joe A. MacGown)
Strumigenys margaritae, head and profile view of dealate queen
Strumigenys margaritae, head and profile view of dealate queen
(drawing by Joe A. MacGown)

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 margaritae Forel, 1893 (Tribe Dacetini) is a tiny predatory ant native to the New World. It is known from northern South America, Central America, Mexico, the West Indies, and the southeastern US from Texas to Florida.

Taxonomic History (provided by Barry Bolton, 2013)
Forel (1893) described Strumigenys margaritae from three sites on the West Indian island of St. Vincent. Bolton (1999) transferred S. margaritae to Pyramica. Baroni Urbani and De Andrade (2007) later synonymized Pyramica with Strumigenys.

Identification
TL 1.9–2.1, HL 0.52–0.58, HW 0.36–0.42, CI 69–73, ML 0.10–0.12, SL 026–0.30, PW 0.24–0.26, WL 0.48–0.56 (measurements from Bolton (2000)).Strumigenys margaritae can be separated from other US dacetine species by the following combination of features: relatively short triangular mandibles with teeth along entire inner borders; presence of reticulate-punctate sculpture on the entire side of the mesosoma; elongate, acute tipped propodeal spines directed posteriorly and slightly upward; lack of spongiform tissue beneath the petiole and base of gaster; and first gastral tergite with rough, grainy, shagreened sculpture.

Two similar species in the same species group (schulzi group), S. epinotalis and S. subnuda, were recently reported from the US (Chen et al. 2012, MacGown and Hill 2010). Strumigenys epinotalis is the only other US species with short mandibles that has dense reticulate-punctate sculpture on the entire head and body. It differs from S. margaritae by having a curved row of spoon-shaped hairs present on the pronotal dorsum; a distinct, wide, convexly curved propodeal lamella; a ventral spongiform crest on the petiole; fan-shaped patches of spongiform tissue on the petiole and postpetiole; and shorter propodeal spines that are directed upward. Strumigenys subnuda, only known from queens,differs by having sparser, less erect, and narrower setation; sculpture lacking on mesopleuron and dorsum of petiole and being shiny in appearance; dentiform propodeal spines; and weakly roughened, somewhat shiny first gastral tergite. Strumigenys inopina is the only other US species with short mandibles that lacks spongiform tissue beneath the petiole. This species is easily separated from S. margaritae by its more narrowly triangular shaped head (in frontal view); the entire side of the mesosoma being shiny; presence of dense, elongate setae on the entire body; and the complete lack of spongiform tissue or lamella-like structures on the waist and gaster.

Biology and Economic Importance
In the southern part of its range, Strumigenys margaritae has been collected most commonly in lowland wet forests, tropical moist forests, mesophil forests, lowland rainforests, tropical rainforests, and montane rainforests (AntWeb data); whereas in the US, it has been most often collected in drier, more open areas such as prairie remnants, pine savannas, scrub, and open disturbed sites (JAM). It has been collected most often from litter samples using Winkler sacks and Berlese funnel extractions, but also by beating or sweeping vegetation, baiting, visual searches, in flight interception traps, and in malaise traps (AntWeb data). On semi-arid Anguilla and St Martin, JKW found S. margaritae only in one area of each island: the sole remnants of intact closed-canopy forest (two sites in Katouche Valley and two sites on the south flank of Mt. Fortune, respectively). Longino (2012) reported that Costa Rican specimens were found in open, disturbed habitats in Pacific lowlands and Meseta Central. Longino (2012) also observed this species visiting extrafloral nectaries of Passiflora pittieri Mast. (Passifloraceae). Specimens from Alabama and Mississippi were collected in Black Belt Prairie remnants by sweeping native vegetation or sifting dead native grasses (JAM). Numerous specimens were collected from southern Louisiana from pitfall traps located in longleaf pine savanna habitat with open grassy understories (JAM). This species has been collected in deep pine and oak litter in waterway scrub in Florida (AntWeb data). Paul Davison (Pers. Comm.) collected a nest of this species in a plaster trap nest that he designed and placed under Quercus alba in upland hardwood forest habitat in northwest Alabama. He noted that of the other Strumigenys species that he had collected with his trap nests, that this was the only one that constructed an earthern shelter insider the plaster cavity. Unlike some of its schulzi group relatives that may actually nest in trees (i.e., S. epinotalis, Chen et al. 2012), S. margaritae appears to prefer lower vegetation (Longino 2012), and although specimens may be collected while foraging in litter, perhaps sweep samples would yield more specimens.

Distribution
South and Central American Distribution: Belize, Colombia, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama, Suriname, and Venezuela.

West Indies Distribution: Anguilla, Antigua, Bahamas, Barbados, Barbuda, British Virgin Isles, Dominica, Dutch Caribbean, Grenada, Guadeloupe, Martinique, Montserrat, Nevis, Puerto Rico, St. Kitts, St. Lucia, St. Martin, St. Vincent, Tobago Trinidad, and US Virgin Isles.

US Distribution: Alabama, Florida, Georgia, Louisiana, Mississippi, and Texas.

Literature Cited

Baroni Urbani, C. & De Andrade, M.L. 2007. The ant tribe Dacetini: limits and constituent genera, with descriptions of new species. Annali del Museo Civico di Storia Naturale “G. Doria” 99: 1-191.

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

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

Chen, X., J.A. MacGown, B. J. Adams, K. A. Parys, R. M. Strecker, and L. Hooper-Bui 2012. First record of Pyramica epinotalis (Hymenoptera: Formicidae) for the United States. Psyche. vol. 2012, Article ID 850893, 7 pages. doi:10.1155/2012/850893

Forel, A. 1893. Formicides de l'Antille St. Vincent, recoltees par Mons. H. H. Smith," Transactions of the Entomological Society of London 1893: 333-418.

Longino, J. T. 2012. Ants of Costa Rica," available online: http://www.evergreen.edu/ants/AntsofCostaRica.html. (Accessed 24 September 2012).

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

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