Key to US Polyergus species

Key to Polyergus species of the United States based on workers, modified from Trager (2013).

1

 * Gastral tergites with pubescence very sparse or lacking, smooth and often strongly shining; North American, most abundant from Atlantic Coast states west to Mississippi Valley (one species extends west to southern Rocky Mountains) (Polyergus lucidus group) =>2
 * Gastral tergites with dense pubescence yielding a silky sheen, obscuring the surface of the integument beneath; Eurasian and North American, in North America from western Great Lakes, prairie and Rocky Mountain states and provinces, to Pacific Coast and Mexican mountains (Polyergus rufescens group) => 7

2

 * Vertex pilose, ½ VeM usually > 10; head and mesosomal dorsum matte and sides at most feebly shining => 3
 * Host Formica dolosa
 * Vertex less pilose, ½ VeM usually < 8; head and mesosomal dorsum matte or shiny; but if matte, then sparsely pilose => 4
 * Host is never Formica dolosa

3

 * Scapes and legs shorter, SI < 105, usually < 100, FI < 140; northern species, New England west to the Dakotas => Polyergus sanwaldi


 * Scapes and legs longer, SI > 100, but usually > 110, FI > 140; southern species, North Carolina to Florida, west to Mississippi and southern Missouri => Polyergus longicornis

4

 * Rear portion of head less pilose, ½ VeM usually < 5; head and mesosoma matte or weakly shining on sides => 5
 * Host Formica pallidefulva or Formica archboldi
 * Rear portion of head pilose, ½ VeM usually > 5; all tagmata at least partly shiny => 6
 * Host Formica incerta or Formica biophilica

5

 * Larger and less pilose species, LI of most specimens > 390; ½ VeM 0–1 (very rarely more); eastern Canada to northern Florida, west to Wisconsin, Colorado, New Mexico => Polyergus montivagus
 * Host Formica pallidefulva


 * Smaller and slightly more pilose, LI of most specimens < 390; ½ VeM 1–5; Florida => Polyergus oligergus
 * Host Formica archboldi

6

 * Smaller, shorter-limbed, SL 1.19–1.36, HFL 1.72–2.04; northeastern, Midwestern, and higher altitude Appalachian distribution => Polyergus lucidus
 * Host Formica incerta


 * Larger, longer-limbed, SL 1.68–1.79, HFL 2.08–2.44; southern and south central USA and foothill Appalachian distribution => Polyergus ruber
 * Host Formica biophilica

7

 * Vertex lacking pilosity or with ½ VeM < 8, usually < 4; pronotal erect pilosity usually all dorsal => 8
 * Hosts in the Formica fusca group, or less often, in the Formica neogagates group, but exclusive of the Formica cinerea complex
 * Vertex notably pilose, ½ VeM > 6, usually 10–30; pronotum always with some erect setae on sides near lower edges => Polyergus breviceps
 * Hosts usually (at least predominantly) Formica montana, Formica canadensis and/or Formica altipetens

8

 * Head and pronotum moderately pilose, ½ VeM < 6 (rarely more), ½ PnM usually > 4; sometimes with infuscated posterior tergites, if gaster appears entirely brown or blackish, ½ PnM > 4 => 9
 * Head and pronotum non-pilose or sparsely pilose, ½ VeM 0, ½ PnM 0–2; distinctly bicolored, head and mesosoma red, gaster entirely dark brown to blackish; western Great Lakes states to Dakotas, Manitoba, usually in moist or bog forests => Polyergus bicolor
 * Host Formica subaenescens (less often Formica neorufibarbis)

9

 * Scapes fall short of vertex corners by a scape width or more, SI < 85; legs shorter, HFI < 120, usually 10
 * Hosts various, but apparently never Formica moki
 * Scapes nearly reaching to slightly surpassing vertex corners, SI > 85, usually > 90; legs longer, HFI > 120; coastal hills of southern California and Baja California => Polyergus vinosus
 * Host Formica moki

10

 * Head often and especially sides of mesosoma weakly to conspicuously shining; scapes not reaching vertex corners by about 1.5–2 scape widths, scapes distally clavate, SI 65–82, but usually < 77; legs shorter, HFI 99–120 (but usually < 113 and always < 110 in southern Arizona and Mexico); upper elevation conifer forests of Mexican mountains, north to British Columbia, Rocky Mountain and Plains states, east to Mississippi Valley => Polyergus mexicanus
 * Hosts are a wide variety of high elevation or northern Formica fusca and Formica neogagates group species


 * Head and mesosoma typically entirely matte, or at most weakly shining; scapes longer, not reaching vertex corners by 1.5 scape widths or often less, scapes thickened distally, but at most weakly clavate, SI 75–86, usually > 79; legs longer, HFI 108–121, usually > 115; HD, Mexico north to lower elevations of southern Arizona mountains in oak or mesquite woodlands => Polyergus topoffi
 * Known hosts are various Mexican, hot climate Formica fusca group species, including Formica gnava, Formica foreliana, Formica subcyanea