Pseudomyrmex ferrugineus

A common species, these ants live in swollen-thorn acacias (=Vachella).

Identification
Ward (1993) - Workers and queens of P. ferrugineus can be recognized by features of head morphology (laterally rounded median clypeal lobe, well separated frontal carinae and correspondingly limited exposure of the median lobes of the antennal sclerites, and moderately broad worker head), head sculpture (densely punctulate and (sub)opaque, but weakly shining on upper third of head between the ocelli and compound eye), and coloration (variably brown, not black or orange-brown). This species is most likely to be confused with the allopatric Pseudomyrmex janzeni and the partly sympatric Pseudomyrmex flavicornis. See under those species for more specific discussion.

Distribution
Eastern and southern Mexico, Guatemala, Belize, El Salvador and Honduras.

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

Biology
A common species, its colonies have been recorded from all swollen-thorn acacia species growing within its range, i.e. Acacia chiapensis (this and the following Acacia species are now classified as Vachellia), A. collinsii, A. cookii, A. cornigera, A. gentlei, A. globulifera, A. hindsii, A. janzenii, A. mayana and ''A. sphaerocephala. Pseudomyrmex ferrugineus'' is usually monogynous (Janzen 1967b, 1973) but a few alcohol nest series from Guatemala, belonging to apparently mature colonies (as judged by the presence of alates), contained more than one dealate queen. Janzen (1966, 1967b) conducted a series of experimental and observational studies of the symbiosis between P. ferrugineus and Vachellia cornigera in Mexico (also see Chapter 14 of the The Ants). The results of this work demonstrated the ants protect their host from herbivores and competing plants. The plants, in turn, provide specialized food and nesting resources to the ants.

Pseudomyrmex ferrugineus was the subject of a study of worker kinship and nestmate recognition (Mintzer 1982; Mintzer et al. 1985). This demonstrated a worker-based and likely genetic component of colony odor.

Pseudomyrmex ferrugineus inhabit a majority of Turnera velutina (previously Acacia hindsii) plants (citations given in Fonseca-Romero et al. 2019), serving the role of a dominant, aggressive ant species that defends the plant. The plant in turn provides nesting space (hollow thorns) and food (extrafloral nectaries and beltian bodies) to the ants.

Nomenclature

 *  ferrugineus. Pseudomyrma ferruginea Smith, F. 1877b: 64 (w.) MEXICO. Combination in Pseudomyrmex: Kempf, 1972a: 218. Senior synonym of bequaerti Wheeler (and its junior synony bequaerti Enzmann), fulvescens, hondurana, saffordi Wheeler, vesana, wasmanni: Ward, 1989: 437. See also: Ward, 1993: 136.
 * fulvescens. Pseudomyrma belti r. fulvescens Emery, 1890b: 64 (w.) GUATEMALA. Forel, 1907e: 7 (m.); Wheeler, W.M. 1942: 160 (q.). Combination in Pseudomyrmex: Kempf, 1972a: 216. Raised to species: Dalla Torre, 1893: 57. Subspecies of belti: Forel, 1899c: 87. Junior synonym of ferrugineus: Ward, 1989: 437.
 * canescens. Pseudomyrma canescens Wasmann, 1915a: 321, pl. 14, figs. 1-4 (w.q.m.) MEXICO. [Junior primary homonym of canescens Smith, above.] Replacement name: wasmanni Wheeler, W.M. 1921b: 92 (footnote).
 * wasmanni. Pseudomyrma wasmanni Wheeler, W.M. 1921b: 92 (footnote). Replacement name for canescens Wasmann, 1915a: 321. [Junior primary homonym of canescens Smith, F. 1877b: 66.] Subspecies of belti: Stitz, 1937: 133; Wheeler, W.M. 1942: 164. Junior synonym of ferrugineus: Ward, 1989: 437.
 * bequaerti. Pseudomyrma belti subsp. bequaerti Wheeler, W.M. 1942: 164 (w.) HONDURAS. Combination in Pseudomyrmex: Kempf, 1972a: 216. Senior synonym of bequaerti Enzmann: Brown, 1949a: 42. Junior synonym of ferrugineus: Ward, 1989: 437.
 * saffordi. Pseudomyrma belti subsp. saffordi Wheeler, W.M. 1942: 162 (w.) MEXICO. Combination in Pseudomyrmex: Kempf, 1972a: 216. Junior synonym of ferrugineus: Ward, 1989: 437.
 * vesana. Pseudomyrma belti subsp. vesana Wheeler, W.M. 1942: 163 (w.) MEXICO. Combination in Pseudomyrmex: Kempf, 1972a: 216. Junior synonym of ferrugineus: Ward, 1989: 437.
 * bequaerti. Pseudomyrma belti subsp. bequaerti Enzmann, E.V. 1944: 80, pl. 2, fig. 17 (w.) HONDURAS. [Unresolved junior primary homonym of bequaerti Wheeler, above.] Junior synonym of bequaerti Wheeler: Brown, 1949a: 42.
 * hondurana. Pseudomyrma kuenckeli var. hondurana Enzmann, E.V. 1944: 87 (w.) HONDURAS. Junior synonym of kuenckeli: Kempf, 1961a: 402; of ferrugineus: Ward, 1989: 437.

Worker
Ward (1993) - Worker measurements (n = 69). —HL 0.99-1.33, HW 0.92-1.15, MFC 0.054-0.108, CI 0.81-0.94, REL 0.42-0.48, REL2 0.48-0.54, OOI 1.39-3.16, VI 0.60-0.78, FCI 0.054-0.101, SI 0.41-0.46, SI2 0.79-0.91, NI 0.61-0.72, PLI 0.54-0.69, PWI 0.56-0.73, PPWI 1.34-1.70.

Medium-sized species (HW > 0.91; LHT 0.75-1.06) with broad head (CI > 0.80); anterior margin of median clypeal lobe straight or weakly concave, rounded laterally; palp formula 5,3; frontal carinae well separated (FCI > O.O5) and median lobe of antennal sclerite not strongly exposed (FCI2 0.45-0.69); mesonotum notably inclined and with basal face of propodeum rounding gradually into declivitous face, but deviations from this pattern occur; petiole relatively short, high and wide (see relevant metrics: PLI, PWI), with a distinct anterior peduncle (PWI3 0.36-0.50); posterolateral angles of petiole moderately developed but not as pronounced as in P. peperi; postpetiole broad. Head densely punctulate, predominantly opaque or subopaque but at least weakly shining on upper third of head between ocelli and compound eye; mesosoma punctulate to punctulate-coriarious, subopaque to sublucid; posterior portions of propodeum opaque to subopaque and usually overlain by larger but weak, irregular punctures or rugulae. Petiole, postpetiole and gaster with fine piligerous punctures, sublucid. Standing pilosity common; pubescence dense but fine and appressed on most surfaces. Color variable, from light reddish- or yellowish-brown to very dark brown, gaster (and usually head) somewhat darker than the mesosoma; mandibles, scapes, frontoclypeal complex, and apices of legs usually lighter.

Type Material
Ward (1993):

Lectotype worker, Mexico [Examined].

Pseudomyrma belti race fulvescens Emery 1 890:64. Lectotype worker, Guatemala (Beccari) [Examined].

Pseudomyrma canescens Wasmann 1915:321. Syntype workers, Tampico, Mexico (Brakhoven) (MCSN, ) [Examined].

Pseudomyrma belti subsp. bequaerti Wheeler 1942:164. Lectotype worker, Puerto Castilla, Honduras (J. Bequaert) (MCZC) [Examined].

Pseudomyrma belti subsp. saffordi Wheeler 1942:162. Lectotype worker, Chicoasen, Chiapas, Mexico (G.N. Collins) (MCZC) [Examined].

Pseudomyrma belti subsp. vesana Wheeler 1942:163. Holotype (unique syntype) worker, Cordoba, Mexico (F. Knab) (MCZC) [Examined].

Pseudomyrma belti subsp. bequaerti Enzmann 1945:80. Syntype workers, Puerto Castilla, Honduras (J. Bequaert) (MCZC) [Examined].

Pseudomyrma kuenckeli var. hondurana Enzmann 1945:87. Lectotype worker, Honduras (Bates) (MCZC) [Examined].