Strumigenys brevicornis

This is a well collected species. It occurs in a range of forest habitats and is most commonly sampled from the litter. In Monteverde, Costa Rica it has been sampled from canopy epiphyte and soil samples. Strumigenys brevicornis also occurs across a wide elevational range. In Costa Rica there is a darker montane form and lighter lower elevation form.

Identification
A member of the crassicornis complex in the Strumigenys gundlachi group.

Longino (Ants of Costa Rica) - Mandibles in full-face view linear, elongate and narrow; ventral surface of petiole without spongiform tissue; leading edge of scape with freely projecting hairs; inner margin of mandible with a clearly defined submedian tooth near the midlength; labral lobes long, trigger hairs at apices of lobes short; preapical denticles gradually decreasing in size; mandibles relatively short (MI 33-45); propodeal suture moderately impressed; total head length less than 0.90mm; eyes relatively small, with 14 or fewer ommatidia, with 2-4 in longest row; head in full-face view relatively broad, CI 74-81; in profile head not strongly dorsoventrally flattened, the maximum depth of the head capsule 0.45-0.52 x head length; color red-brown to dark brown; pair of mesonotal setae conspicuous, often erect or tilted forward; erect hairs on first gastral tergite remiform or markedly flattened and expanded apically; backcurved pair of stout hairs located posteriorly on petiole dorsum thickly remiform; scape relatively long, SI 53-60. Also see Bolton (2000:180).

Variation: this is a case where, in Costa Rica at least, there is a larger, darker montane form (see discussion of montane dark forms). The light form has head length less than 0.75mm, and the mesonotal setae are usually spatulate and tilted forward. The dark form has head length 0.75-.090mm, and the mesonotal setae often relatively filiform, erect or tilted somewhat to rearward. To me they appear sympatric and largely discrete on the lower Atlantic slopes (50-800m). However, Bolton has examined these and other specimens and considers them to be one species (brevicornis). Also, Brown (1959) examined five Costa Rican collections of what he identified as brevicornis. One of the collections was from "Tablazo," a montane site, and was described as being dark brown rather than the lighter ferrugineous of other collections. He stated "The dark brown specimens (Tablazo) apparently come from a highland area in Costa Rica that has produced melanic variants of many wide-ranging dacetine species."

Distribution
Widely distributed and relatively common in Central America

Distribution based on Regional Taxon Lists
Neotropical Region: Belize, Costa Rica, Guatemala, Honduras, Mexico, Nicaragua, Panama.

Biology
Brown (1959) summarized species in this now synoymized genus Neostruma as having "small colonies, chiefly in the leaf litter of rain forest or tropical evergreen forest, and nests occupy cavities in rotting twigs, pieces of bark or similar forest-floor vegetable debris... The food... consists primarily of small entomobryomorph Collembola and possibly some other minute terrestrial arthropods as well."

Longino (Ants of Costa Rica) - This species inhabits wet forested habitats from near sea level to 2600m, the light form most abundant below 500m, the dark form most abundant above. It occurs in leaf litter and is common in Winkler samples. A Winkler sample from oak forest in the Talamancas (Cerro Gemelos) at 2600m yielded six workers of this species and one worker of a Discothyrea species. This is one of the highest records of ants in Costa Rica (the only higher record I know is for a nomadic army ant, Labidus coecus, at 3000m near Villa Mills). At Monteverde the species is common in litter on the ground, but has also been taken in Winkler samples of epiphytes and soil from the forest canopy (also see Longino's discussion of variation within this species in the identification section above).

Nomenclature

 *  brevicornis. Strumigenys brevicornis Mann, 1922: 38 (w.q.) HONDURAS. Combination in Neostruma: Brown, 1948e: 111; in Pyramica: Bolton, 1999: 1673; in Strumigenys: Baroni Urbani & De Andrade, 2007: 116. Senior synonym of mustelina: Bolton, 2000: 180. See also: Brown, 1959b: 10.
 * mustelina. Strumigenys (Strumigenys) mustelina Weber, 1934a: 34, fig. 11 (q.) MEXICO. Brown, 1959b: 7 (w.m.). Combination in Neostruma: Brown, 1959b: 7; in Pyramica: Bolton, 1999: 1672. Junior synonym of brevicornis: Bolton, 2000: 180.

Worker
Bolton (2000) - TL 1.7-2.2, HL 0.41-0.55, HW 0.34-0.43, CI 74-81, ML 0.16-0.22, MI 36-45, SL 0.16-0.26, SI 53-60, PW 0.24-0.30, AL 0.43-0.58 (52 measured). Characters of crassicornis complex. Dentition variable, with 4 - 6 denticles between apicodorsal tooth and submedian tooth and with 1 - 5 denticles proximal of the submedian tooth. Apex of mandible with 4 - 5 minute intercalary denticles between apicodorsal and apicoventral teeth. Eye with 2 - 3 ommatidia in longest row, very rarely with 4; with 5 - 9 ommatidia in total. Leading edge of scape evenly convex, without an abrupt lobate expansion at the subbasal angle. Head capsule in profile not strikingly dorsoventrally flattened, the maximum vertical distance between highest and lowest points 0.45-0.52 X HL. Spongiform lobes of postpetiole small but obvious. Standing hairs on dorsal petiole and postpetiole remiform; those on the first gastral tergite remiform or flattened and expanded apically.

Widely distributed and relatively common in Central America, this small species shows colour forms varying from yellow-brown to black, with intermediate shades. In general darker coloured samples are somewhat larger and usually occur at greater altitude than lighter individuals.

Type Material
Syntype workers and queen, HONDURAS: Ceiba, ii-iii. 1 920, No. 24458 (W.M. Mann) (examined).

Strumigenys (Strumigenys) mustelina Weber, 1934a: 34, fig. 11. Syntype queens (alate), MEXICO: Vera Cruz Prov., Jicoltepec, San Rafael (examined).