| 1 | Petiole pedunculate to subpedunculate, in lateral view the anterodorsal margin of the gaster forms a single convexity that ascends posterad at approximately 45° (Fig. 1A) | 2 |
| – | Petiole sessile, not subpendunculate, in lateral view the anterodorsal margin of the first gaster segment forming a much steeper slope (>45°) with a more or less distinct vertical anterior face (Fig. 1B) | 4 |
| 2 | Dorsal surface of the head with deep striation that reaches to the nuchal collar; color uniform ferruginous to dark red | O. davidsoni sp. nov. |
| – | Posterior third to half of dorsal surface of head smooth and shining; color variable | 3 |
| 3 | Without metasternal process; mesonotum almost hairless; larger body size (HL > 4 mm). Ground living | O. mormo |
| – | With metasternal process; dorsal surface of mesonotum covered in small erect setae; smaller body size (HL < 3.8 mm). Arboreal | O. hastatus |
| 4 | Dorsal surface of head distinctly striate to or nearly to the nuchal carina | 5 |
| – | Posterior third to half of dorsal surface of head smooth and shining, or nearly so | 22 |
| 5 | Disc (dorsal surface) of first gastric segment predominantly smooth, punctulate, alutaceous, or reticulate; striation absent, or if present, mixed with other sculpture and distinct only on the posterior half of the disc | 6 |
| – | Disc of first gastric segment distinctly and evenly striate over its entire surface, at least as seen from dorsal view | 17 |
| 6 | Mesonotum longitudinally striate | O. yucatecus Brown, 1976 |
| – | Mesonotum prevailingly transversely striate | 8 |
| 7 | Head more or less bright red (frontal area often infuscate), contrasting with blackish-brown body and yellow legs; size medium | O. erythrocephalus |
| – | Color combination otherwise; if head is distinctly red, then trunk is red also, or legs are dark | 8 |
| 8 | Sternum immediately in front of and between metathoracic coxae produced as a slender, acute pair of teeth or spines; disc of first gastric segment densely and finely shagreened and pubescent, usually opaque; body brown, legs yellow to brown | O. haematodus (Linnaeus, 1758) |
| – | Sternum in front of metathoracic coxae with a low transverse ridge, sometimes notched in the middle or bilobed, but not produced as acute, paired teeth | 9 |
| 9 | Petiole predominantly smooth and shiny, with the anterior border erected or slightly convex, and the apex produced into a large spine with posterior orientation; head, mesosoma and petiole with a clear red coloration and the gaster dark brown | O. insularis Guérin-Méneville, 1844 |
| – | Petiole differently shapes, color combination varies | 10 |
| 10 | Anterior face of petiolar node as seen from the side rising steeply from anterior margin, then passing through an obtuse angle into a long section concave in outline to the root of the apical spine; labial palpi 4-merous | O. bradleyi Brown, 1976 |
| – | Petiole differently shaped | 11 |
| 11 | Metasternal process like an arc with or without middle division; petiole smooth or a little striate, with both the anterior and posterior margin convex; the petiolar spine forms gradually, without clear distinction from petiole | O. cf. brunneus Patton, 1894 (possibly Odontomachus ruginodis; O. brunneus is apparently restricted to southeastern US. The status of the Central and South American populations comparable with O. brunneus need to be established.) |
| – | Metasternal process absent, bilobed or triangular; petiole differently shapes or if both sides convex, with a clear differentiation of the spine from the rest of the petiole | 12 |
| 12 | Metasternal process absent | 13 |
| – | Metasternal process bilobed or triangular | 14 |
| 13 | Black coloration; Node of petiole with a pair of prominent posterolateral tumosities at about mid-height and without striation; apex as seen from side abruptly narrowed to an axially erect, acute tooth | O. biumbonatus Brown, 1976 |
| – | Node of petiole without paired posterolateral tumosities; Posterior face of petiole less concave, with short petiolar spine (0.1 mm) | O. clarus Roger, 1861 |
| 14 | Anterior margin of petiole at least weakly convex | 15 |
| – | Anterior margin of petiole basal of the node concave or straight | 16 |
| 15 | Metasternal process completely bilobed; color generally dark | O. bauri Emery, 1892 |
| – | Metasternal process formed by an obtuse wide lobe followed by a transverse flange which is produced into a triangular process; usually light color | O. biolleyi Forel, 1809 |
| 16 | Petiole strongly transversely striate, with a clearly differentiated spine; small species (TL 8.6–9.35 mm) | O. ruginodis Smith, 1937 |
| – | Petiole without or only weak striation and with spine not clearly differentiated from the petiole; large species (TL 12 mm) | O. laticeps Roger, 1861 |
| 17 | First gaster segment with only one type of sculpture, which is either punctulate or striate | 18 |
| – | First gaster segment with a combination of punctulate and reticulate sculpture | 21 |
| 18 | First gaster segment punctulate on its entire surface | O. opaciventris Forel, 1899 |
| – | First gaster segment striate on most of its surface, at least in dorsal view | 19 |
| 19 | Transverse striation patterns on the gaster; large and slender | O. chelifer (Latreille, 1802) |
| – | Longitudinal striation on the dorsal gaster surface | 20 |
| 20 | Mesonotum strongly convex, but broadly sulcate and longitudinally striate on at least the anterior half near midline | O. caelatus Brown, 1976 |
| – | Mesonotum gently but evenly convex, transversely striate | O. laticeps |
| 21 | Mesonotum with longitudinal striation | O. scalptus Brown, 1978 |
| – | Mesonotum with transverse striation | O. meinerti Forel, 1805 |
| 22 | Ocular prominences each produced anterolaterally into a stout, acute, oblique, toothlike process | O. cornutus Stitz, 1933 |
| – | Ocular prominences bluntly rounded, as usual | 24 |
| 23 | Antennal scapes very short, not reaching posterior border of head in full-face view; very small species with broad head | O. spissus Kempf, 1962 |
| – | Antennal scapes surpassing posterior border of head viewed full-face | 24 |
| 24 | Apex of mandible with only 2 large teeth (intercalary tooth lacking) | O. allolabis Kempf, 1974 |
| – | Apex of mandible with 3 teeth | 25 |
| 25 | Mesepisternum with a prominent, narrowly rounded anteroventral lobe projecting conspicuously on each side when trunk is viewed from above | O. mayi Mann, 1912 |
| – | Mesepisternum with at most a low, inconspicuous convexity on its anteroventral margin | 26 |
| 26 | Petiole clearly differentiated spine; larger species (HL > 2.8 mm) | O. affinis Guérin-Méneville, 1844 |
| – | Both faces of petiole converge into a thick spine that is flattened laterally; smaller species (HL < 2.8 mm) | O. panamensis Forel, 1899 |