Trachymyrmex

A genus of fungus growing ants. Trachymyrmex is mostly Neotropical, occurring in the Nearctic region mostly in the southern parts of Florida, Texas and Arizona, except for one species. Trachymyrmex septentrionalis that occurs up to New York in the North, Illinois, Texas, and Louisiana in the west, and south to Florida and the West Indies. Long Island and Staten Island in New York are the northernmost records for an attine ant. (Mayhé-Nunes & Brandão 2002)

Identification
Mayhé-Nunes & Brandão (2002) - The most clear feature to distinguish the monomorphic Trachymyrmex from other attine cognate genera is the always present mesosomal projections on the dorsum of pronotum and/or mesonotum, surmounted by secondary tubercles or minute teeth, that in some species are transformed in small blunt hillocks. All species of Atta lack dorsal projections on the pronotum, and show in addition a strong variation of total body length amongst workers of the same colony. Acromyrmex and Mycetosoritis, the probable closest genera to Trachymyrmex, share with most Trachymyrmex the tuberculated dorsal surface of the first gastric tergite. There are some Trachymyrmex species that look very similar to Acromyrmex workers, which are, nonetheless, almost as polymorphic as in Atta. On the other hand, Trachymyrmex differs from the enigmatic Mycetosoritis by their relatively shallow antennal scrobes (deeply impressed in Mycetosoritis) only comparable to the scrobes found in the Strigatus group of Cyphomyrmex. Most Cyphomyrmex of the Rimosus group have the frontal lobes very expanded laterally, clearly surpassing two thirds of the head width. although two species of this group, Cyphomyrmex longiscapus and Cyphomyrmex foxi show weakly expanded frontal lobes while, in the strigatus group, Mycetophylax lectus and Mycetophylax bruchi present extremely expanded frontal lobes.

The extremely homogeneous Sericomyrmex differs from the strikingly heterogeneous Trachymyrmex in the females by having heart-shaped head, broadest posteriorly, broader than long, lacking any trace of occipital tooth and supraocular tumulus; the preocular carina fades out before or at the level of posterior orbit of eye; the frontal lobes are always triangular and inconspicuously expanded laterad, the interfrontal width about one half of head width as measured across the eyes; the antenna! scapes are relatively short, never quite reaching the occipital border in full-face view when laid back over the head as much as possible; thorax compact; piligerous tubercles practically absent.

Trachymyrmex species groups

Species Uncertain
An unknown species of Trachymyrmex is a host for the diapriid wasp (www.diapriid.org).

Species Uncertain
The generic placement of the following species is uncertain. Species formerly placed in Trachymyrmex are now placed within Trachymyrmex, Mycetomoellerius and Paratrachymyrmex.
 * “Trachymyrmex” sp. 1, 2n=12 (n=6), karyotype=12M, Panama, Murakami et al. (1998).
 * “Trachymyrmex” sp. 2, 2n=18 (n=9), karyotype=18M, Panama, Murakami et al. (1998).
 * “Trachymyrmex” sp. 3, 2n=22 (n=11), karyotype=18M + 4SM, Brazil, Barros et al. (2013).

Nomenclature

 *  TRACHYMYRMEX [Myrmicinae: Attini]
 * Trachymyrmex Forel, 1893e: 600 [as subgenus of Atta]. Type-species: Atta septentrionalis, by subsequent designation of Wheeler, W.M. 1911f: 174.
 * Trachymyrmex subgenus of Cyphomyrmex: Emery, 1913b: 251; Emery, 1924d: 344.
 * Trachymyrmex subgenus of Acromyrmex: Forel, 1917: 247.
 * Trachymyrmex raised to genus: Gallardo, 1916b: 242; Wheeler, W.M. 1916c: 11; Wheeler, W.M. 1922a: 669; Borgmeier, 1950b: 384; Kempf, 1972a: 252.

Taxonomic Notes
Kempf was in the process of revising Trachymyrmex at the time of his death. Brandao and Mayhe-Nunes subsequently used Kemp's manuscripts when revising the genus in a series of papers that focused on individual species groups.

Worker
Mayhé-Nunes & Brandão (2002) - Dorsal mesosomal spines multidentate or multituberculate, often transformed into small blunt hillocks, bristling with secondary tubercles. Frontal carinae strongly diverging caudad reaching or nearly reaching the lateral angles of the occiput, forming laterad a sometimes shallow but always present scrobe for part of the scapes. Inter frontal width close to or less than 2/3 of the head Width (including eyes). Worker caste monomorphic or nearly so, size Variation slight; major workers absent.