Key to Formica species in or possible in MS and AL (from Creighton 1950 and J. C. Trager, pers. comm.)
1 The combined length of the second and third segments of the funiculus not more than one and one-fifth times the length of the first segment and usually not that long (not likely in this area)
...neogagates Viereck (neogagates group)
  The combined length of the second and third segments of funiculus at least one and one-fourth times the length of the first segment and usually longer
2 The anterior margin of the clypeus with a concave impression medially, which is either broad and shallow or narrow and notch-like
...3 (sanguinea group)
  Anterior margin of clypeus lacking a median notch or impression
3(2) Profile of alitrunk angulate (dorsally), having a "saddle-back" appearance with the declivious face of the propodeum descending at a right angle to the plane of the dorsal face; the petiolar crest blunt
  The alitrunk profile less angular, the junction of propodeal declivity and dorsal face more rounded; petiolar crest sharp
4(2) The scape is notably longer than the distance from the middle of the border of the clypeus to the middle of the occipital border; the angle between the dorsal face of the propodeum and the declivity is poorly marked giving the propodeum a rounded appearance above
...5 (pallidefulva group)
  The scape is not longer than the distance from the middle of the border of the clypeus to the middle of the occipital border, or if longer then the propodeum is distinctly angular and not excessively rounded above

First gastral tergite with appressed pubescence of medium to high density, the average distance between the individual appressed setae approximately equaling the average length of setae to much less; alitrunk dorsum with several to many erect setae on pronotum, mesonotum and propodeum (setae often most numerous on the latter); various open grassland, heath, or dry savanna and open woodland habitats (occasionally in mesic forests in the deep South)

  Gaster shiny with sparse, short appressed pubescence; alitrunk dorsum without erect setae or with a small cluster on the mesonotum and/or a few erect hairs elsewhere; color highly variable, ranging from bright tawny or coppery yellow (south) to very dark brown (North and western mountains) and many intermediate colorations; mesic habitats, from gardens, parks and prairies to closed-canopy forests
6(5) Gaster with dense pubescence, first gastral tergite with appressed setae separated by about 0.5 or less the average setal length; alitrunk dorsum feebly or (at some viewing angles) not shining; propodeum often with conspicuous pubescence; alitrunk and gastral integument dulled by fine, but notable sculpture

Gaster less densely pubescent; first gastral tergite with appressed setae separated by about 0.75-1.0 X their average length; alitrunk and gastral integument somewhat shining, with diffuse sculpture

7(6) Widely distributed in eastern US (rare west of 100th meridian); reddish-brown (Northeast) to light reddish (Southeast, Midwest); alitrunk and gastral integument dulled or velvety looking with dense pubescence, in larger workers appearing matte in dorsal or oblique dorsal view; numerous erect macrochaetae on all dorsal surfaces, those on first tergite usually long, tapering and typically curved
  Not widely distributed (AL, FL and GA); dark brown to blackish brown; with fine coriaceous sculpture on alitrunk and foveolae on gastral dorsal surface; erect setae shorter and fewer, at least on alitrunk, erect setae may be blunt-tipped and without notable curvature, even on first gastral tergite
8(6) Cuticle weakly shining (shinier in Great Lakes region, especially the gaster); color dingy yellowish or reddish brown with gaster or head and gaster a little to significantly darker (overall darker northeast); erect setae of gastral dorsal surface straight or weakly curved, blunt-tipped or abruptly or weakly tapering, length of the longest macrochaetae 0.15-0.22 mm (not very likely, more northern)
  Alitrunk dorsal integument a little more shining to quite smooth; color bright reddish-yellow or with gaster a little darker (gaster of this species sometimes stains black in mounted specimens); erect setae of gastral dorsal surface curved and tapering, length of longest macrochaetae 0.20 – 0.30 mm
9(4)  Occipital border of large workers distinctly concave; in profile the pronotum not evenly convex, with a dorsal and a declivious face which meet in an angle
...exsectoides Forel (exsecta group)
  The occipital borders of large workers at most slightly concave, but usually flat or slightly convex; the pronotum evenly convex as seen in profile and not angular
10(9) Bicolored, head and alitrunk ferrugineous or yellowish red and lighter than gaster (if infuscated, then infuscations does not totally mask the reddish ground color in larger workers); the frontal area squally shining and frontal lobes strongly divergent posteriorly
...11 (rufa group)
  Concolorous brownish black to piceous black; frontal area opaque and frontal lobes often parallel or at most only moderately divergent posteriorly
..subsericea Say (fusca group)
11(10) The median lobe of the clypeus descends abruptly to the clypeal fossae through steep side faces that make an angle with the upper face of the lobe; fossae on clypeus are deep, pit-like, and the anterior edge of the clypeus that bounds them in front sweeps up in an even curve to the median lobe (possible, not very likely
  Median lobe of clypeus descends an even curve that begins at the carina; the fossa of clypeus are shallow, scarcely pit-like and the edge of the clypeus in front of the fossae is very broadly united to the base of the lobe and does not form a distinct curve with it
12(11) Erect hairs on mid and hind tibia confined to a double row of bristles on flexor surface and rarely only one or two erect hairs elsewhere
  Erect hairs on mid and hind tibia abundant (usually) and covering all surfaces with at least a number of erect hairs in addition to those on flexor surface (not likely in this area)