Polyergus nigerrimus

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Biology
Marikovsky studied P. nigerrimus in the summer of 1960. In his description, Marikovsky (1963) noted that the specimens were taken with abundant host workers of Formica candida in shrub steppe near the Yenisei River. Marikovsky reported a diffuse nest, with 7 entrances over a 10m2 area, but only the central one had a well developed infrastructure and large population, including alates of both sexes, and an ergatoid. He described a raid involving about 400 nigerrimus workers, in the “evening when the sun was setting down” and ending during “falling darkness”. Despite attempts by the F. candida to bite the raiders and to wrest their pupal quarry from them, the nigerrimus simply pushed on home without attacking any of the defending Formica workers. Returning nigerrimus workers initially placed the stolen pupae in two of the peripheral nests, but later transferred the pupae to the main nest about 0.5m away.

Trager (2013) updated the identification of the host with Marikovsy’s sample as F. candida, using Seifert’s (2004) key. Marikovsky had identified them as F. gagates, and Kupyanska (1990) mentions F. picea as the host, also a species previously confused with F. candida. Kupyanskaya calls this an ant of the steppe, and Antonov (2008) also reports habitat of this ant as the steppe. Its host, by implication, in the Antonov study is F. candida (the only abundant potential host at the location). Antonov comments that nigerrimus “is extremely rare in natural habitats,” but this may be an artifact of collecting intensity. The Formica kozlovi host record is from a collection made by Martin Pfeiffer in Mongolia (also note Pfeiffer’s images of nigerrimus at http://antbase.net/htdocs/formicinae/polyergus/polyergus_nigerrimus_marikovsky,_1963.html). Dubatalov (1998) also reports this ant from Mongolia.

Nomenclature

 *  nigerrimus. Polyergus nigerrimus Marikovsky, 1963: 110, figs. 1-7 (w.q.m.) RUSSIA. See also: Kupyanskaya, 1990: 208.

Worker
Trager (2013) - Syntypes (N=7) HL 1.32–1.44 (1.40), HW 1.24–1.36 (1.32), SL 1.00–1.06 (1.03), ½ VeM 1–9 (4.71), ½ PnM 5–7 (6.29), WL 2.12–2.20 (2.17), GL 1.76–2.00 (1.93), HFL 1.60–1.68 (1.64), CI 94–96 (94.4), SI 74–81 (79), HFI 119–130 (125), FSI 157–160 (159), LI 3.48–3.60 (3.56), TL 5.24–5.60 (5.49).

Smallish, TL averaging 5.5mm; blackish, weakly shining species of the Asian steppes. Head rounded hexagonal (truncate-ovate), its length detectably greater than breadth; with conspicuous vertex pilosity; scapes not reaching vertex, notably clavate in the apical third; pronotum with 10–14 dorsal erect setae; mesonotum with profile flat or very weakly convex for most of its length, with a short posterior declivity; propodeal profile subquadrate, taller than pronotum, with concave declivity profile; petiole with sides round, converging dorsad, petiolar dorsum emarginate; first tergite densely pubescent, with pilosity in 3 or 4 irregular transverse rows, first tergite pilosity gently curved, longer than the distance separating the individual setae.

Head weakly shining; mesonotum weakly shining dorsally, a bit smoother laterally; gaster weakly shining to matte dorsally, somewhat shiny laterally.

Color black to nearly black; legs and scapes dark brown; pilosity gray-brown.

Etymology
Trager (2013) - This name is from the Latin superlative adjective “nigerrimus”, meaning very black or blackest. A hand written label accompanying the series reads “nigricans”, meaning blackish, but this name never reached publication.