Key to the species of Myrmecina in the southeastern United States
(from Stefan Cover, Harvard MA, pers. comm.)

1 Usually larger in size, but some specimens smaller; usually mostly black in color, occasionally reddish brown; heavily sculptured on alitrunk and head; postpetiole with a tiny, sharp ventral tooth
  Much smaller; reddish colored; head and alitrunk dorsum smooth and shiny: postpetiole with a large, blunt ventral tooth
...sp.