Dacetini, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Images of dark form specimen: lateral view (original, reduced); face view (original, reduced).
Range
Full Range: southern Mexico to Panama.
Costa Rican Range: common throughout, from sea-level to 2600m.
Identification
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."
Natural History
Brown (1959) characterized the genus Neostruma (now part of Pyramica, see Bolton 1999) as forming
"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. Hunting behavior is like that of Smithistruma [also now part of Pyramica] rather than like the Strumigenys so far studied."
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.
Selected Records (light form)
Winkler samples from La Selva Biological Station, Turrialba, Hitoy Cerere, Penas Blancas Valley (800m), Monteverde (900m elevation on road to Monteverde, moist forest remnant), Santa Rosa National Park ("Bosque Humedo"), Carara Biological Reserve, Manuel Antonio National Park, Corcovado National Park, 19km S. Ciudad Neily.
La Selva: nest in dead wood on forest floor.
Selected Records (dark form)
Winkler samples from the Talamancas (Cerro Gemelos and Estacion Biologica Pittier), San Vito area, Turrialba, Rara Avis, La Selva, Penas Blancas Valley, Monteverde, Guanacaste Conservation Area (Pitilla).
Original Description
Strumigenys brevicornis Mann 1922:38. Syntype worker, queen: Honduras, La Ceiba, ii-iii.1920, No. 24458 (Mann) [USNM, MCZ].
Later moved to Neostruma, then Pyramica. See Bolton (2000) for complete synonymy.
Literature Cited
Bolton, B. 1999. Ant genera of the tribe Dacetonini (Hymenoptera: Formicidae). J. Nat. Hist. 33:1639-1689.
Bolton, B. 2000. The ant tribe Dacetini, with a revision of the Strumigenys species of the Malagasy Region by Brian L. Fisher, and a revision of the Austral epopostrumiform genera by Steven O. Shattuck. Memoirs of the American Entomological Institute 65:1-1028.
Brown, W. L., Jr. 1959. A revision of the Dacetine ant genus Neostruma. Breviora 107:1-13.
Mann, W. M. 1922. Ants from Honduras and Guatemala. Proceedings of the U. S. National Museum 61:1-54.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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