Polyergus ruber

Primarily a southeastern United States species, Polyergus ruber raids nests of and tracks the range of its host Formica biophilica.

Identification
This is among the three largest species of the lucidus group, almost in the same size range as longicornis, but characterized by a shinier head and mesosoma, especially the pronotum, and less abundant pilosity, especially on the vertex. Color is clear red with at most slight infuscation of the extremities.

P. ruber appears intermediate between longicornis and lucidus in its proportions, pilosity, and shininess. The sheen and lesser vertex pilosity distinguishes ruber from the more matte longicornis (ruber ½ VeM < 12 vs. longicornis > 13) while the longer appendages distinguish it from lucidus (ruber SI > 92+ vs. lucidus < 91).

Distribution
Polyergus ruber tracks its host, Formica biophilica, in distribution, namely, a U-shaped range south from Maryland to Georgia, west to Louisiana, then north to eastern Missouri. It would be unsurprising if this ant showed up from collecting in at least southern Illinois.

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

Biology
Polyergus ruber was studied by Vargo and Gibbs (1987, reported as lucidus longicornis) in Athens, Georgia. Aside from its unique host association with, ruber seems much like its relatives in the lucidus group in most respects. Raids were observed from early June to mid-August, and may have continued after these observations ended, as the activity was still vigorous, so perhaps starting just a few weeks earlier and persisting perhaps a bit longer than in other species of the group. I observed parts of a raid, and a mating flight that occurred several hours before the raid, in Georgia, and two raids of these ants in Missouri, all in July, and they are much like those of the other species. At both locations, pre-raiding milling was initiated around 1700 hr. The size of raiding parties in the Georgia colonies was estimated between 500 and 1000, quite large compared to other known lucidus group species. Colonies and raiding parties were somewhat smaller in Missouri. Vargo and Gibbs observed dealate gynes near the outskirts of nests before raids in late July, and saw one of these follow a raid and enter the raided nest. Habitats of this species included a variety of upland, grassy and open woodland types, with acid soils.

Nomenclature

 *  ruber. Polyergus ruber Trager, 2013: 528, figs. 39-41 (w.q.m.) U.S.A.

Worker
Holotype HL 1.90, HW 1.80, SL 1.79, ½ VeM 9, ½ PnM 3, WL 2.86, GL 2.60, HFL 2.44, CI 95, SI 99, HFI 136, FSI 136, LI 4.76, TL 7.36.

Paratype (N=5) [MCZ, CAS, FSCA] HL 1.60–1.90 (1.75), HW 1.52–1.80 (1.64), SL 1.68–1.79 (1.71), ½ VeM 3–9 (6.8), ½ PnM 1–4 (2.2), WL 2.52–2.86 (2.66), GL 2.04–2.60 (2.34), HFL 2.09–2.44 (2.26), CI 93–95 (94), SI 99–113 (105), HFI 134–146 (138), FSI 124–136 (132), LI 4.12–4.76 (4.41), TL 6.16–7.36 (6.75).

(N=26) HL 1.52–1.90 (1.65), HW 1.42–1.80 (1.64), SL 1.68–1.79 (1.71), ½ VeM 3–9 (6.8), ½ PnM 1–4 (2.2), WL 2.52–2.86 (2.66), GL 2.04–2.60 (2.34), HFL 2.09–2.44 (2.26), CI 93–95 (94), SI 99–113 (105), HFI 124–136 (132), FSI 124–136 (132), LI 4.12–4.76 (4.41), TL 6.16–7.36 (6.75).

This species is most similar to Polyergus longicornis, but is shinier and has less pilosity. Head rectangular to weakly hexagonal, HL greater than HW; with conspicuous vertex pilosity consisting of (5) 8–20 erect macrosetae; scapes at least reaching, normally surpassing vertex corners, gradually thickening in distal half; pronotum with 0–6 dorsal erect setae; mesonotal profile weakly convex for most of its length; propodeal profile variable ranging from evenly rounded to a weakly obtuse, rounded angle; petiole narrow, sides convex and converging dorsad, petiolar dorsum rounded or with median portion flat, less often feebly concave; first tergite lacking pubescence; first tergite pilosity sparse, weakly flexuous or straight.

Head matte to very faintly shining; mesosoma matte dorsally but shining laterally; gaster weakly shining to shiny.

Etymology
With the name ruber, Latin for red or ruddy, I refer to the brighter, all-red color of this ant species, in comparison to other southeastern species, especially the somewhat similar, but dark-legged longicornis.

References based on Global Ant Biodiversity Informatics

 * Ivanov K., L. Hightower, S. T. Dash, and J. B. Keiper. 2019. 150 years in the making: first comprehensive list of the ants (Hymenoptera: Formicidae) of Virginia, USA. Zootaxa 4554 (2): 532–560.
 * Trager J. C. 2013. Global revision of the dulotic ant genus Polyergus (Hymenoptera: Formicidae, Formicinae, Formicini). Zootaxa 3722(4): 501-548.