Pseudomyrmex fortis

Aggressive ants that act quickly to defend their nesting plant.

Identification
Ward (1999) - Key distinguishing features of P. fortis are the relatively large size yet elongate head (worker CI 0.81–0.86, queen CI 0.72–0.73), relatively short eyes in relation to head length (worker REL 0.57–0.59, queen REL 0.53–0.56), broad and subglobose petiole, with prominent anteroventral process, and unicoloured body. The worker has well separated frontal carinae and a broad profemur (FI > 0.47). P. fortis bears little close resemblance to Pseudomyrmex sericeus which is smaller (worker HW < 0.95), with closely contiguous frontal carinae, elongate eyes (worker REL ≈ 0.65), a short high propodeum whose basal and declivitous faces meet at an angle, and a petiole which is subtriangular in lateral profile.

Distribution
Mexico, Central America, Colombia and Venezuela.

This taxon was described from Mexico.

Biology
Ward (1999) - Little is known about its biology, but Wheeler (1913, 1942) reported the species inhabiting Triplaris melaenodendron (as T. auriculata) at Patulul and Escuintla, Guatemala, and he indicated that the workers sting readily. Wheeler & Bailey (1920:264) examined larval food pellets of these P. fortis and found remains of insects, fungi, and bits of “medullary tissue evidently gnawed from the walls of the myrmecodomatia by the workers”. A population of P. fortis in northern Colombia — with somewhat divergent morphology, the workers being small with short petioles — also has aggressive workers, which inhabit live Avicennia branches and tend coccids of the genus Cryptostigma (Ward, 1991). I suspect that P. fortis will prove to be a “generalist” plant-ant species, i.e. one which, like Pseudomyrmex viduus, Pseudomyrmex rubiginosus, and some Azteca species (Longino, 1996), occupies a variety of live plant cavities.

Nomenclature

 *  fortis. Pseudomyrma sericea var. fortis Forel, 1899c: 89 (w.) MEXICO. Combination in Pseudomyrmex: Kempf, 1972a: 223. Raised to species: Ward. 1999b: 520.

Worker
Ward (1999) - Measurements (n=10). HL 1.14–1.38, HW 0.96–1.15, MFC 0.038–0.068, LHT 0.72–0.93, CI 0.81–0.86, REL 0.57–0.59, REL2 0.67–0.71, FCI 0.04–0.06, FI 0.48–0.50, PLI 0.90–1.10, PWI 0.81–0.92.

Worker description. A member of the sericeus group. Palp formula: variable (6,4 or 5,4). Frontal carinae well separated; head somewhat elongate, sides weakly convex; posterior margin of head concave, in frontal view. Profemur broad; legs relatively short (LHT/HL 0.62–0.70). Dorsal face of propodeum subequal in length to declivitous face, and rounding gradually into it; propodeal spiracle distant from basal (dorsal) face of propodeum. Petiole subglobose, rounded in profile, with a single convex anterodorsal face, which rounds gently into the steep posterior face. Anteroventral process well developed, a triangular or subrectangular lobe, usually with a blunt posteroventral tooth or angle. Standing pilosity sparse; stout, paired setae usually present on pronotum (1–2 pairs), propodeum at junction of basal and declivitous faces (0–1 pair), petiole (1 pair) and postpetiole (1–2 pairs), occasionally additional short hairs present on mesosoma. Dark brown to brownish black; mandibles and frontoclypeal complex a lighter castaneous brown; scape, protibia and protarsus may also be a lighter brown.

Type Material
Ward (1999) - Syntype worker, Atoyac, Veracruz, Mexico (H. H. Smith) [Examined].