Polyergus montivagus

Found from northeastern to midwestern North America, this species exclusively raids nests of Formica pallidefulva.

Identification
Polyergus montivagus is most easily distinguished from other Nearctic species by its shining gaster, lack or near lack of pilosity, and association with Formica pallidefulva. In the Northeast, its proportions approach those of Polyergus sanwaldi, but in absolute metrics montivagus is smaller, and is nearly non-pilose. Where sympatric with Polyergus lucidus, the latter is distinguished by the presence of 5 or more erect setae on the vertex corners, as opposed to never more than 4 (usually 0–2) in montivagus. Where sympatric with Polyergus oligergus, montivagus is again distinguished by host preference, dark legs of mature specimens, and by its slightly larger size, average slightly shorter scapes and hind femora, and slightly less pilosity. Gynes of montivagus are notably larger than those of oligergus. Indicative of this, WL almost 3.0 mm compared to about 2.5 mm, respectively, in three specimens of each that were available for measuring.

Distribution
Trager (2013): Although originally described from Colorado, and almost nowhere abundant, this species is now known to blanket nearly the entire distribution of its host, Formica pallidefulva, though typically restricted to sites with sandy or at least well drained soil. F pallidefulva's range extends from the eastern United States and southeastern Canada, then west across the US Great Plains to the lower-elevation Rocky Mountains from Wyoming to New Mexico.

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

Biology
Trager (2013): Talbot (1967, 1968) and Marlin (1968, 1969, 1971) studied this ant’s behavior, reported as lucidus but determined by vouchers I have seen from their studies. Polyergus montivagus is an ant of meadows surrounded by woods, grassy areas that are shaded part of the day, sandy or loessic open woodlands, park-like habitats and lawns, where an abundance of the host species occurs. Its host is always (King & Trager, 2007; Trager, 2013; de la Mora et al., 2021). Talbot (1967) saw a colony in Michigan of montivagus with F. pallidefulva (reported as F. p. nitidiventris) that raided F. neogagates & F. lasioides, but brood of these species never survived to adulthood as workers in the Polyergus nest. There is a notable trend toward smaller colonies to the South and West. One colony dug by Talbot (1967) in Michigan contained 291 montivagus workers, 299 montivagus pupae, and over 4500 F. pallidefulva workers. I observed a raid by about 130 montivagus workers in southern Iowa, Marlin (1969) reported an average of 87 raiders in central Illinois, and I estimated a colony near Boulder, Colorado to have 90–100 workers. A colony dug by King (King and Trager 2007) contained 70 Polyergus and over 500 F. pallidefulva workers. Raids that Talbot (1967) saw in Michigan occurred from mid June to early September. Marlin (1969) observed raids in Illinois from early June through mid September. These dates correspond to the periods when host worker pupae are most available. Raids take place late afternoon till dusk. Marlin and Talbot agreed in most details of the flight behavior of montivagus. Marlin (1971) described flight activity as follows: “Males left the nests only during the late morning and early afternoon (10 AM to 3 PM). They appeared in groups of five to 30 and milled about the nest area. On 9 days in 1966 males were active at one nest that produced no females that year. Alate gynes were active from noon until after 7 PM. On 10 days gynes left the nest without males.” He also noted that females usually flew off, but saw two instances of females mating on the ground near the nest.

Nomenclature

 * montivagus. Polyergus lucidus subsp. montivagus Wheeler, W.M. 1915b: 419 (w.q.m.) U.S.A. Junior synonym of lucidus: Creighton, 1950a: 557. Revived from synonymy and raised to species: Trager, 2013: 526.

Worker
Trager (2013) - (N=32) HL 1.40–1.70 (1.55), HW 1.40–1.68 (1.51), SL 1.34–1.58 (1.44), ½ VeM 0–4 (0.53), ½ PnM 0–3 (0.29), WL 2.28–2.76 (2.46), GL 1.96–2.80 (2.29), HFL 1.92–2.24 (2.09), CI 93–104 (97), SI (83, one specimen) 88–104 (96), HFI 130–149 (135), FSI 138–156 (145), LI 3.68–4.44 (4.00), TL 5.68–7.16 (6.28).

Head truncate-ovoid to subhexagonal, wider behind eyes, sides anterior to eyes straight or even weakly concave and convergent toward mandibular bases, head length usually slightly greater than breadth; vertex pilosity 0–2 erect setae present near each corner (4 on one side of a single specimen); scapes at least reaching, normally surpassing vertex corners, gradually thickening apically; pronotum with 0–2 (very rarely up to 5) dorsal erect setae; mesonotal profile weakly convex; propodeum profile a rounded right angle; petiole with weakly convex sides converging dorsad, petiolar dorsum flat or at most weakly concave emarginate; petiolar profile low, its apex when gaster is in horizontal position only a little higher than propodeal spiracle, petiolar front and rear surfaces convergent dorsad, front weakly convex, rear straight; first tergite lacking pubescence; first tergite pilosity 0–6 relatively short suberect macrosetae.

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

Color red, often with notably darker, even nearly blackish legs; scapes and mesometapleura infuscated; what little pilosity is present is dark brown.

Specimens from the southeastern portion of the range have a more gracile appearance, with proportionally longer appendages, and have somewhat smaller colony size than those elsewhere.

Etymology
Trager (2013) - Wheeler coined this adjectival name from Latin “mons, monti-” (hill) and “vagus” (wandering), apparently in reference to its discovery in the foothills of the Rocky Mountains.

References based on Global Ant Biodiversity Informatics

 * Deyrup M. 2016. Ants of Florida: identification and natural history. CRC Press, 423 pages.
 * Hayes W. P. 1925. A preliminary list of the ants of Kansas (Hymenoptera, Formicidae). [concl.]. Entomological News 36: 69-73
 * Hill J.G. & Brown R. L. 2010. The Ant (Hymenoptera: Formicidae) Fauna of Black Belt Prairie Remnants in Alabama and Mississippi. Southeastern Naturalist. 9: 73-84
 * Trager J. C. 2013. Global revision of the dulotic ant genus Polyergus (Hymenoptera: Formicidae, Formicinae, Formicini). Zootaxa 3722(4): 501-548.