Polyergus oligergus

Unusual for Polyergus in having a relatively small range, this Florida native raids nests of Formica archboldi.

Identification
Smaller size, more vertex pilosity, proportionally and often absolutely longer hind femora, higher values for any proportion using HFL and most with SL, and association with Formica archboldi distinguish this species from the similar Polyergus montivagus.

Polyergus oligergus apparently lives only in Florida and only with F. archboldi. It is quite similar to montivagus, but averages visibly smaller than the average for that species, has a lower petiole, tends to be slightly more pilose, and has smaller colony populations. Further P. montivagus often has dark brown to blackish legs, while those of P. oligergus are usually only slightly darker, if at all, than body color. Gynes and males of P. oligergus are significantly smaller in every dimension than those of P. montivagus.

Distribution based on Regional Taxon Lists
Nearctic Region: United States.

Biology
A colony dug by King (King and Trager, 2007) contained 40 mature Polyergus workers, with 340 (King & Trager, 2007; Trager, 2013; de la Mora et al., 2021) workers. Near Gainesville Florida, I observed numerous raids by 4 colonies, with from 25–38 raiders participating (Trager and Johnson, 1985). One remarkable raid observed after that paper was published, was carried out successfully by four P. oligergus workers against a small F. archboldi colony. Each of the 4 raiders emerged alive and bearing a pupa, while the estimated 100+ F. archboldi workers and their gyne rushed out of the nest and climbed up nearby plant stems or hid under leaf litter. Raids that Trager and Johnson (1985, reported as lucidus) saw in Florida occurred from mid-May through July (with one outlier in early September). I observed alates flying off from the nests between 11:00 and noon, about 6 hours before brood raids on the same day, on clear dry days in July. The colony from Putnam Co., Florida contained a single, significantly larger, presumably ergatoid, individual.

Nomenclature

 *  oligergus. Polyergus oligergus Trager, 2013: 527, figs. 36-38 (w.q.m.) U.S.A.

Worker
Holotype HL 1.41, HW 1.37, SL 1.48, ½ VeM 2, ½ PnM 0, WL 2.26, GL 2.18, HFL 1.98, CI 97, SI 108, HFI 145, FSI 134, LI 3.67, TL 5.85.

Paratype (N=9) HL 1.36–1.56 (1.45), HW 1.31–1.52 (1.41), SL 1.40–1.58 (1.49), ½ VeM 0–3 (1.56), ½ PnM 0–1 (0.33), WL 2.16–2.48 (2.30), GL 2.08–2.28 (2.20), HFL 1.98–2.16 (2.06), CI 96–98 (97), SI 99–111, HFI 139–156, FSI 134–143 (139), LI 3.52–4.04 (3.75), TL 5.72–6.32 (5.96).

(N=44) HL 1.32–1.66 (1.48), HW 1.28–1.63 (1.45), SL 1.40–1.61 (1.51), ½ VeM 0–5 (2.55), ½ PnM 0–2 (0.93), WL 2.09–2.68 (2.36), GL 1.70–2.60 (2.09), HFL 1.98–2.32 (2.15), CI 94–102 (98), SI 93–113 (104), HFI 139–161 (148), FSI 134–154 (143), LI 3.48–4.34 (3.85), TL 5.23–6.94 (5.96).

Head ovoid to subhexagonal, widest just behind eyes, sides anterior to eyes often slightly concave, the two sides appearing parallel from eyes to mandibular bases, head length usually only slightly greater than breadth; vertex pilosity (0) 2–5 macrosetae present near each corner; scapes at least surpassing vertex corners, gradually thickening apically, SI 93–113 (values below 100 for an ergatoid and a few other very large workers); pronotum with (0)1–4 dorsal erect setae; mesonotal profile weakly convex for most of its length; propodeal profile rounded with nearly flat portions of dorsal and posterior faces meeting at about a curved right angle; petiole with rounded sides converging dorsad, petiolar dorsum flat or at most weakly concave; petiolar profile low, normally not reaching height of propodeal spiracle, petiolar front and rear surfaces convergent dorsad, front convex, rear straight; first tergite lacking pubescence; first tergite pilosity 0–6 relatively short suberect macrosetae.

Head very faintly shining; mesonotum weakly shining, shinier on lateral pronotum; gaster shiny.

Color red with somewhat darker legs, scapes and mesometapleura; what little pilosity is present is a bit lighter than main body color.

Etymology
This species has the smallest worker populations of any Polyergus species. The name stems from Greek, olig- (few) plus erg- (work), roughly meaning few workers, and alliterating neatly with the genus name.

References based on Global Ant Biodiversity Informatics

 * Trager J. C. 2013. Global revision of the dulotic ant genus Polyergus (Hymenoptera: Formicidae, Formicinae, Formicini). Zootaxa 3722(4): 501-548.