Key to Brachymyrmex species in the Southeastern United States
The species in Brachymyrmex are not clearly worked out and there could be several new species involved in the group, thus the names used here should be considered somewhat "temporary" in nature.  There appears to be at least two undescribed species in FL, one in MS, and one in AR.
1
Queens minute, approximately the same size of workers; dark brown (rare, known only from Arkansas, possibly a social parasite of B. depilis-Lloyd Davis, pers. comm.)
...sp.-04
Queens normal sized, much larger than workers; color variable
...2
2(1) Color pale yellow to yellowish-brown
...3
  Color reddish-brown to blackish-brown
...7
3(2) No erect hairs on dorsum of head, alitrunk, or gaster (except on edges of gastral tergites)
...4
  Erect hairs on dorsum of head and alitrunk
....5
4(3)
Eye larger, approximately six to eight facets in greatest diameter (common, widespread species)
Eye smaller, only three to four facets in greatest diameter (possible new species, rare, only known from FL)
5(3) Scattered short, stiff, erect hairs present on femora; erect hairs on gaster limited to edges of tergites, lacking on tergal plates themselves
  Femora lacking erect hairs; scattered erect hairs present on gastral plates (as well as edges)
...6
6(5) Gaster with numerous appressed hairs; scape long; head oval-rectangular, longer than wide; alitrunk narrow, twice longer than wide; ocelli sometimes present; metanotal groove weak; light yellow to yellowish red (only know from FL)
  Gaster with scattered appressed hairs; scape shorter; head rectangular, to almost as wide as long; alitrunk shorter and wider; ocelli absent; metanotal groove very conspicuous; yellowish to yellowish brown (also keys later, possible, tropical species)
...heeri Forel
7(2) Erect hairs absent on dorsum of head, alitrunk and gastral tergites (except along edges); sparse pubescence, very shiny (only know from FL)
...sp.-01 (formerly called brevicornis)
  Erect hairs present on dorsum of head, alitrunk and gastral tergites (except along edges)
...8
8(7)
Eyes much shorter than the length of the malar space; gaster, especially the first tergite, densely covered with appressed pubescence, giving a more opaque, softer appearance; body and legs concolorous brown to blackish (exotic, southern MS-rare and FL-common, especially in the southern portion of the state)
Eyes larger, about as long as the length of the malar space; gaster with more sparse pubescence, more shiny in appearance; head, alitrunk, and petiole reddish-brown with legs somewhat lighter, gaster dark brown to blackish
...9
9(8) Ocelli present in all castes (hard to see in workers; exotic, very common in gulf coast states)
  Ocelli absent in workers (possible, tropical species)
...heeri Forel