Polyergus rufescens

The lone European Polyergus species, Polyergus rufescens has a wide range that extends to western Asia.

Identification
Trager (2013): This is the unique Polyergus species of Europe and western temperate Asia, and appears morphologically to be closely related to the breviceps group, particularly the essentially Mexican species Polyergus topoffi. Future genetic study should deepen our understanding of the relationships of this apparent outlier of what is otherwise a western North American group, distinguished from all other red Polyergus by its Eurasian distribution. It is most similar to Polyergus topoffi among the American species, differing by its slightly (average) narrower head and petiole, and denser, more regular array of bent or strongly flexuous, decumbent pilosity on the first tergite. Specimens from western and especially southwestern Europe are darker in color than those from Asia. Populations of central western Europe have a more pilose vertex than those from the Iberian Peninsula, northern and eastern Europe, and central Asia (½ VeM usually 2–12, compared to ½ VeM 0–2). Lighter color and reduced pilosity were noted as characteristic of the subspecies tianschianicus in Kuznetsov-Ugamsky’s (1927) description, but in fact, color variation seems to be a west to east clinal feature, and the reduced pilosity is a characteristic of peripheral populations, as it is also found in samples from the far west of the range. Thus, the two traits do not covary. In any case, the subspecies are indistinguishable by any other ecological, metric or obvious morphological characters; hence, Trager's (2013) synonymy of this subspecies.

Distribution
Trager (2013): Found from Atlantic western Europe east to mountains of western China and “Central Asia”. Extending to 57°N and 88°E, then south to the Caspian, Black, and Mediterranean Coasts.

Distribution based on Regional Taxon Lists
Palaearctic Region: Albania, Armenia, Austria, Belarus, Belgium, Bulgaria, China, Croatia, Czech Republic, France , Georgia, Germany, Greece, Hungary, Iberian Peninsula, Italy, Kazakhstan , Kyrgyzstan, Luxembourg, Netherlands, Norway, Poland, Portugal, Republic of Macedonia, Republic of Moldova, Romania, Russian Federation, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey.

Biology
Trager (2013): The “classical” summaries of the behavior of this ant are from Huber (1810) and Wheeler (1910). In the last decade or so, a number of papers, especially those by le Moli’s Laboratory in Italy, have refined our knowledge of this species, particularly regarding the role of secondary compounds in regulating their behavior (Castracani et al. 2003, 2005, 2008; Grasso et al. 2003, 2004, 2005; Le Moli et al. 2001; Romani et al. 2006; Visicchio et al. 2001, 2003, 2007). The following natural history is paraphrased from a summary kindly provided by Bernhard Seifert (pers. comm., 2009) “P. rufescens is characteristic of dry, semi-dry and sparse grasslands of any sort that supports sufficiently dense host populations. Hosts vary geographically and include a variety of species: Formica cunicularia (16 observations), Formica fusca (12), Formica rufibarbis (10), Formica clara (3), Formica gagates (3) and Formica cinerea (1). Local host species preferences are obvious, and considering the whole distributional range, host species selection appears to be a trade-off between host species abundance and mortality risk—strong and aggressive colonies of F. clara and F. cinerea are only attacked in the absence of less resistant alternatives. In many regions of Central Asia, F. clara is a main host, as it is a dominant species there and has smaller workers than in Central Europe.” And from Roland Schultz (pers. comm., 2012) “The host of P. rufescens in cases from Kyrgyzstan, Kazakhstan and western China is F. clara. Formica clara is the most common “Serviformica” in the high steppes of the Tianshan Mountains of China and Kyrgyzstan, at the altitudes in which also Polyergus appears, below 2500 m. In one case, Seifert found 5 workers of F. exsecta, including one freshly eclosed from the pupa, among a lot of F. clara and P. rufescens.” In a sample from the Tarbagatai Mountains Kazakhstan, Schulz confirmed a mix of F. clara and F. rufibarbis as hosts. In addition, I have series from the Pyrenees with Formica gerardi, where this is the most abundant potential host. Seifert’s abundance/trade-off hypothesis seems plausible and testable; there is much opportunity for careful study of host selection in this species (as also in the quite polylectic North American Polyergus mexicanus).

List of Known Hosts
This species is known to enslave the following species:
 * (3 observations)
 * (16 observations)
 * (12 observations)
 * (3 observations)
 * (10 observations)
 * (10 observations)
 * (10 observations)

Nomenclature

 *  rufescens. Formica rufescens Latreille, 1798: 44 (w.q.) FRANCE. Schenck, 1852: 70 (m.); Forel, 1874: 137 (gynandromorph); André, 1882b: 163 (w.q.m.); Wheeler, G.C. & Wheeler, J. 1968: 214 (l). Combination in Polyergus: Latreille, 1804: 179. Senior synonym of testacea: Smith, F. 1858b: 57; tianschanicus: Trager, 2013: 510. Current subspecies: nominal plus laeviceps, mexicanus. See also: Stitz, 1939: 369; Hölldobler, 1985: 225; Trager, 2013: 510.
 * testacea. Formica testacea Fabricius, 1804: 400 (q.) CZECHOSLOVAKIA. [Unresolved junior primary homonym of Formica testacea Gmelin, in Linnaeus, 1790: 2804.] Junior synonym of rufescens: Smith, F. 1858b: 57.
 * tianschanicus. Polyergus rufescens subsp. tianschanicus Kuznetsov-Ugamsky, 1927c: 41, figs. 1-6 (w.q.m.) KAZAKHSTAN. Junior synonym of rufescens: Trager, 2013: 510.

Worker
Trager (2013) - (N=41) HL 1.23–1.72 (1.59), HW 1.20–1.66 (1.51), SL 0.99–1.31 (1.22), ½ VeM 0–11 (2.41), ½ PnM 3–13 (6.8), WL 1.96–2.60 (2.37), GL 1.44–2.18 (2.13), HFL 1.36–1.92 (1.78), CI 90–99 (95), SI 77–88 (81), HFI 110–130 (1.18), FSI 136–155 (146), LI 3.23–4.32 (3.96), TL 4.67–6.98 (6.14).

Head subrectangular, its length greater than breadth; with conspicuous vertex pilosity (usually 6–12 setae) on most specimens from more western locations and no vertex pilosity (0–1 seta) on specimens from farther east; scape apex reaching about 1/4 the distance between eye and vertex corner, weakly clavate in the apical third, or gradually thickening apically; pronotum with (6)10–20 (25) erect setae; mesonotum with profile flat or very weakly convex for most of its length; propodeum evenly rounded; petiole high, its profile about equal in height to propodeum, petiole straight-sided, petiolar dorsum convex, not emarginate or weakly emarginate; first tergite densely pubescent, with numerous, bent or strongly flexuous, decumbent pilosity concentrated in anterior half of sclerite.

Head matte; mesonotum matte; gaster matte.

Color deep red (especially west) to orangey red (especially east) with weak to notable infuscation (deep, often purplish tinted, brown) of pleura, gaster and appendages in darker individuals.

Etymology
Trager (2013) - Latreille coined this name from the Latin verbal form “rufescens”, meaning reddish or fading to red.