Pseudomyrmex simplex

Prefers to nest in dead twigs as opposed to the hollowed out stems of herbaceous vegetation.

Identification
Ward (1985) - This species is the smallest one of a trio of orange Pseudomyrmex (Pseudomyrmex pallidus, Pseudomyrmex  seminole, P. simplex) which have been confused repeatedly in the United States. P. simplex workers are recognizable by their smooth, shiny, puncticulate head; broad forefemur (FI ≥ 0.45); and shining fourth abdominal tergite which is devoid of a dense mat of appressed pubescence. In addition the workers have long eyes, closely contiguous frontal carinae, a very shallow metanotal groove, and a short petiole and postpetiole. The simplex and delicatulus types share these essential features, along with the other material which I have examined. There is a fair range of variation in size and body proportions (see metrics). P. simplex tends to be lighter in color than related species, and the fuscous patches on abdominal tergite IV are usually conspicuous, at least in Florida populations (less so in Central and South America).

Distribution based on Regional Taxon Lists
Nearctic Region: United States. Neotropical Region: Argentina, Bahamas, Belize, Brazil, Colombia, Costa Rica, Cuba, Dominican Republic, Ecuador, El Salvador, Greater Antilles, Grenada, Guatemala, Haiti, Honduras, Jamaica, Mexico, Panama, Paraguay, Peru, Puerto Rico, Trinidad and Tobago, Venezuela.

Biology
Ward (1985) - P. simplex shows a preference for nesting in dead twigs of woody shrubs or trees, rather than in dead stalks of herbaceous plants. In Florida, I have collected nests in dead twigs or stalks of Baccharis halimifolia, Cladium jamaicense, Laguncularia racemosa, Metopium toxiferum and Nectandra coriacea; there are also museum records from Carya floridana and Swietenia mahagoni.

In Costa Rica I recorded nests of P. simplex in dead twigs of Anacardium, Ardisia revoluta, Avicennia germinans, Conocarpus erectus, Gliricidia sepium, Hibiscus tiliaceus, and Terminalia catappa.

Most P. simplex nests I dissected were queenless (indicating a high level of polydomy), some were monogynous, and one contained two functional (i.e. inseminated, with well-developed ovaries) dealate queens.

Alates have been collected in May, June, and September in Florida.

Gillette et al. (2015) in a Chaipas, Mexico field study of twig-nesting ants in coffee plants found P. simplex was by far the most abundant ant in lower elevation (< 1000 m) sites, occupying 80% of all occupied nests.

Koch et al. (2018) sampled this species in Caryocar barsiliense trees, in southeastern Brazil cerrado, as part of a study examining species interactions in ant-plants.

Nomenclature

 *  simplex. Pseudomyrma simplex Smith, F. 1877b: 64 (w.) BRAZIL. Combination in Pseudomyrmex: Kempf, 1972a: 223. Senior synonym of capperi, delicatula, panamensis and material of the unavailable name vittata referred here: Ward, 1985b: 238. See also: Ward, 1992: 75 (specimen in amber).
 * capperi. Pseudomyrma delicatula var. capperi Forel, 1899c: 93 (w.) JAMAICA. Combination in Pseudomyrmex: Kempf, 1972a: 215. Subspecies of flavidula: Wheeler, W.M. 1913d: 240. Junior synonym of simplex: Ward, 1985b: 238.
 * delicatula. Pseudomyrma delicatula Forel, 1899c: 93, pl. 4, fig. 6 (w.q.) JAMAICA. Wheeler, W.M. 1913b: 484 (m.). Combination in Pseudomyrmex: Kempf, 1972a: 215. Subspecies of acanthobius: Forel, 1907e: 7; of flavidulus: Wheeler, W.M. 1913b: 484; Wheeler, W.M. 1913d: 240; Wheeler, W.M. & Mann, 1914: 17. Junior synonym of simplex: Ward, 1985b: 238.
 * panamensis. Pseudomyrma delicatula var. panamensis Forel, 1899c: 93 (w.) GUATEMALA. Combination in Pseudomyrmex: Kempf, 1972a: 215. Junior synonym of simplex: Ward, 1985b: 238.

Type Material
Ward (1985, 1989):

Holotype (unique syntype) worker. Sao Paulo de Olivenca ["St. Paul"], Amazonas, Brazil [Examined].

Pseudomyrma delicatula Forel. 1899. Syntype workers, one dealate queen. Kingston, Jamaica (Forel) [Examined.]

Pseudomyrma delicatula var. panamensis Forel, 1899. Holotype (unique syntype) worker. Pantaleon, Guatemala. 1700 ft (Champion) (MHNG) [Examined].

Pseudomyrma delicatula var. capperi Forel, 1899. Syntype workers. Jamaica (Capper) (MHNG) [Examined].

Pseudomyrma acanthobia race delicatula. var. vittata Forel, 1912. Syntype workers. Ceara, Brazil (Rocha) (MHNG) [Examined].

Worker
Ward (1985) - Measurements (n = 46): HL 0.70-0.92, HW 0.55-0.74, MFC 0.009-0.017, CI 0.75-0.85, OI 0.49-0.55, REL 0.52-0.61, REL2 0.62-0.77, OOI 0.55-1.92, VI 0.68-0.83, FCI 0.013-0.025, SI 0.40-0.48, SI2 0.56-0.72, FI 0.45-0.52, PDI 1.27-1.94, MPI 0.005-0.043, NI 0.53-0.65, PLI 0.50-0.69, PWI 0.39-0.60, PPWI 0.97-1.31.

Diagnosis. —Relatively small species, with moderately elongate head (HW 0.55-0.74, CI 0.75-0.85); median portion of anterior clypeal margin straight, laterally angulate; frontal carinae very closely contiguous (minimum distance between them much less than the basal width of scape); eyes relatively long (REL 0.52-0.61); occipital margin concave, flat, or slightly convex, in full face, dorsal view; lateral margins of pronotum rounded: metanotal groove very weak and shallow; basal face of propodeum longer than declivitous face, and more or less clearly differentiated from it; petiole relatively short, with an anterior peduncle and anteroventral tooth; postpetiole often wider than long, somewhat globose in lateral view. Head predominately smooth and shining; frons with scattered fine punctures of variable size, on a smooth or obsoletely coriarious background; punctures less dense on the vertex, which is smooth and shining; mesosoma and petiole sublucid, dorsally weakly coriarious-punctulate, laterally coriarious-imbricate; postpetiole and gaster more or less smooth and shining. Erect pilosity sparse, lacking on mesonotum, propodeum, mid and hind femora, and (often) petiole: typically a pair of erect setae on pronotum, postpetiole, and adjacent to the eyes. Fine, appressed pubescence very sparse, notably so on postpetiole and abdominal tergite IV. Light orange brown, mandibles and clypeus a paler luteous; a pair of anterolateral fuscous patches usually present (sometimes weak) on abdominal tergite IV.

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