Pseudomyrmex spinicola

This is a common species that is an obligate acacia mutualist. It is typically found nesting in Vachellia collinsii trees but can also inhabitant a few other Vachellia  species.

Identification
Ward (1993) - The short, broad, emarginate and laterally angulate median clypeal lobe distinguishes the worker of this species. The sublucid integument, elongate petiole, prominent propodeal spiracles, and somewhat angulate posterolateral corners of the petiole are also characteristic. In addition, queens and workers of P. spinicola have more elongate scapes and legs than those of all other species except Pseudomyrmex satanicus. For differences between P. spinicola and the closely related P. satanicus see under the latter species.

P. spinicola is a variable taxon and has received several infraspecific names, here considered junior synonyms. Southeastern populations (from the Rio Grande de Tarcoles in Costa Rica east through Panama to northern Colombia) are somewhat differentiated from the others, with the workers and queens tending to have more elongate heads, darker color, and more slender petioles with less pronounced posterolateral angles. In Costa Rica the contrasts between the two sets of populations are rather striking, and are perhaps accentuated by habitat differences since some (but not all) the southeastern populations are associated with Acacia allenii growing in forested situations, while the northern populations are primarily from Acacia collinsii in open habitats. Samples from Panama (all associated with A. collinsii) are more variable and partly bridge the phenotypic gap. It is possible that more than one species is masquerading in this variation but the evidence remains ambiguous.

Distribution
Ranging from Honduras to Colombia.

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

Biology
Ward (1993) - A monogynous species associated with Acacia collinsii and, less frequently, Acacia allenii and A. cornigera. Janzen provides a good summary of its biology in Costa Rica, under the name "P. ferruginea" (Pseudomyrmex ferrugineus). Observations on "P. ferruginea" in Costa Rica, Nicaragua, Panama and Isla Providencia (Janzen 1969, 1974, 1975, 1983) refer to Pseudomyrmex spinicola; true P. ferrugineus does not occur south of Honduras and El Salvador.

Amador-Vargas (2019) found that P. spinicola made larger clearings around the trees they occupied than Pseudomyrmex flavicornis and Pseudomyrmex nigrocinctus. Pseudomyrmex spinicola workers also pruned thicker vegetative tissue, and their workers had broader heads - presumed to allow more robust pruning due to larger muscles in the head providing greater mandibular force. More generally, this study and its findings are unusual in examining plant pruning differences provided by ants involved in acacia mutalisms. Most studies of ant-provided benefits to plants in these ant-plant mutualisms focus on herbivory.

Nomenclature

 *  spinicola. Pseudomyrma spinicola Emery, 1890b: 64, pl. 6, fig. 2 (w.q.m.) COSTA RICA. [Also described as new by Emery, 1894k: 52.] Combination in P. (Triangulinoda): Enzmann, E.V. 1944: 61; in Pseudomyrmex: Wheeler, G.C. & Wheeler, J. 1956: 386. Senior synonym of atrox, gaigei, infernalis Wheeler (and its junior synonym infernalis Enzmann), scelerosa Wheeler (and its junior synonym scelerosa Enzmann): Ward, 1993: 149.
 * atrox. Pseudomyrma spinicola r. atrox Forel, 1912g: 24 (w.) PANAMA. Combination in Pseudomyrmex: Kempf, 1972a: 224. Junior synonym of spinicola: Ward, 1993: 149.
 * gaigei. Pseudomyrma spinicola r. gaigei Forel, 1914c: 615 (w.) COLOMBIA. Combination in Pseudomyrmex: Kempf, 1972a: 224. Junior synonym of spinicola: Ward, 1993: 150.
 * infernalis. Pseudomyrma spinicola subsp. infernalis Wheeler, W.M. 1942: 180 (w.q.m.) PANAMA. Combination in Pseudomyrmex: Kempf, 1972a: 224. Senior synonym of infernalis Enzmann: Brown, 1949a: 43. Junior synonym of spinicola: Ward, 1993: 150.
 * scelerosa. Pseudomyrma spinicola subsp. scelerosa Wheeler, W.M. 1942: 181 (w.) NICARAGUA. Combination in Pseudomyrmex: Kempf, 1972a: 224. Senior synonym of scelerosa Enzmann: Brown, 1949a: 43. Junior synonym of spinicola: Ward, 1993: 150.
 * infernalis. Pseudomyrma spinolae var. infernalis Enzmann, E.V. 1944: 91 (w.q.m.) PANAMA. [The name spinolae is a misspelling of spinicola.] [Unresolved junior primary homonym of infernalis Wheeler, above.] Junior synonym of infernalis Wheeler: Brown, 1949a: 43.
 * scelerosa. Pseudomyrma spinolae var. scelerosa Enzmann, E.V. 1944: 91 (w.) NICARAGUA. [The name spinolae is a misspelling of spinicola.] [Unresolved junior primary homonym of sclerosa Wheeler, above.] Junior synonym of scelerosa Wheeler: Brown, 1949a: 43.

Worker
Ward (1993) - measurements (n=4l). HL 0.99-1.28, HW 0.94-1.15, MFC 0.032-0.067, CI 0.84-0.97, REL 0.42-0.47, REL2 0.45-0.54, OOI 1.22-2.77, VI 0.64-0.83, FCI 0.032-0.061, SI 0.45-0.50, SI2 0.88-1.05, NI 0.61-0.69, PU 0.47-0.64, PWI 0.49-0.71, PPWI 1.32-1.85.

Median clypeal lobe emarginate, laterally angulate, relatively broad (CLW/HW 0.21-0.25). Palp formula 5,3 (rarely 5p4,3). Frontal carinae relatively close, and median lobes of antennal sclerites rather exposed (FCI2 0.24-0.42). Head longer than broad but variably so (see range of CI values). Posterior margin of head ranging from broadly convex to straight or even weakly concave, usually rounding gently into the sides of head. Basal face of propodeum subequal to declivitous face, rounding into latter; in dorsal view propodeal spiracles salient, protruding laterally. Petiole generally slender (PU <0.65) with a well developed anterior peduncle; in dorsal view posterolateral angles typically prominent. Head densely punctulate, sublucid, interspaces small (punctulae essentially contiguous on most of head) but shiny. Mesosoma finely punctulate dorsally becoming punctulate-coriarious laterally, sublucid; propodeum lacking overlying, coarser rugulo-punctate sculpture. Standing pilosity usually moderately common on body dorsum and including some hairs > 0.20 mm. Appressed pubescence common on most surfaces. Varying from light orange-brown to dark brown in color.

Type Material
Ward (1989) - Syntype workers, queens, males, Alajuela, Costa Rica (Alfaro) [Examined]. One worker here designated LECTOTYPE.

Ward (1993):

Pseudomyrma spinicola race atrox Forel 1912:24. Syntype workers, Panama (Christophersen) [Examined]. One syntype from MHNG here designated LECTOTYPE.

Pseudomyrma spinicola race Gaigei Forel 1914:615. Syntype workers, Columbien (Gaige) (MHNG), Fundacion, Colombia (F. M. Gaige) [Examined].

Pseudomyrma spinicola subsp. infernalis Wheeler 1942:180. Syntype workers, queens, males, Venado, Canal Zone, Panama (W. M. Wheeler), Red Tank, Canal Zone, Panama (W. M, Wheeler), and Las Sabanas, Panama (W. M. Wheeler) (, MCZC) [Examined]. One MCZC worker, from Red Tank, here designed LECTOTYPE.

Pseudomyrma spinicola subsp. scelerosa Wheeler 1942:181. Syntype workers, Granada, Nicaragua (C. F. Baker) (AMNH, MCZC) [Examined]. One MCZC worker here designated LECTOTYPE.

Pseudomyrma spinolae [sic] var. infernalis Enzmann 1945:9 1. Syntype workers, queens, Red Tank, Canal Zone, Panama (W. M. Wheeler) (MCZC) [Examined].

Pseudomyrma spinolae [sic] var. scelerosa Enzmann 1945:91. Syntype workers, Granada, Nicaragua (C. F. Baker) (MCZC) [Examined].