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Key to Tetramorium species in the southeastern United States

(from Creighton, 1950 and Bolton, 1979)
1      Erect hairs on mesosomal dorsum branched or trifid, dense; promesonotum strongly arched (in profile); sculpture on head and mesosoma coarse rugulate, giving impression of many tightly woven, almost circular pits next to one another, surface texture somewhat opaque in appearance; dark brown
  Erect hairs on mesosomal dorsum simple, less dense; promesonotum not strongly arched, but more straight to weakly curved; sculpture variable, weak to coarsely rugulate
...2
2 (1)     Anterior clypeal margin with a distinct notch or indentation; yellow brown to darker brown, often bicolored with gaster darker; (this species historically was misidentified as T. guineese)
  Anterior clypeal margin entire, without notch or indentation; color variable, yellow brown to dark brown or bicolored
...3
3 (2)    Hairs on mesosomal dorsum numerous, of varying lengths, fine and generally acute apically; head and mesosoma dark brown, dark reddish brown, or blackish brown

 

 Hairs on mesosomal dorsum sparse, of similar length, short, stout and blunt apically; head and mesosoma (sometimes also gaster) yellow or yellowish brown
...4
4 (3) Frontal carinae strong, sinuate, extending almost to occipital region and surmounted by a narrowly raised rim or flange for entire length; antennal scrobes shallow, but broad and obvious; ground sculpture between frontal carinae granular to reticulate punctate, opaque in appearance; propodeal spines longer
  Frontal carinae more weakly developed, only extending to approximately the level of mid length of eye, then becoming weak or broken, not surmounted by a rim or flange beyond level of eye; antennal scrobes vestigial; sculpture between frontal carinae weaker, more shining in appearance; propodeal spines shorter, triangular

***Note: Another introduced species, T. tsushimae Emery, has been found in Missouri, but has not yet been found in the Southeast. It is quite similar in appearance to T. immigrans, but differs by being smaller and having longer propodeal spines.