| 1a. | Tiny ant, antennae with 10 segments; no propodeal spines; tiny eyes (< 15 ommatidia) | Solenopsis |
| 1b. | Antennae with 11 or 12 segments | 2 |
| | | |
| 2a. | Antennae with 11 segments | 3
|
| 2b. | Antennae with 12 segments | 6 |
| | | |
| 3a. | Gaster heart-shaped; petiole attached dorsally to gaster | Crematogaster
|
| 3b. | Gaster not heart-shaped; petiole attachment anterior | 4 |
| | | |
| 4a. | Frontal carina short, no antennal scrobe (groove in which antenna sits) | 5 |
| 4b. | Frontal carina longer (extending beyond eye), forming an antennal scrobe | Protomognathus americanus |
| | | |
| 5a. | Eyes with short, erect hairs between the ommatidia | Fromicoxenus provancheri
|
| 5b. | Eyes without erect hairs between the ommatidia | Leptothorax (muscorum group)
|
| | | |
| 6a. | Petiole short, no scale or node, and with no anterior peduncle. Two pairs of propodeal spines | Myrmecina americana |
| 6b. | Petiole usually with a node and distinct anterior peduncle. 0 or 1 pair of propodeal spines | 7 |
| | | |
| 7a. | Posterolateral portions of clypeus raised into a sharp ridge ("carina") that forms an antennal socket.Sting with small triangular appendage on dorsal end. On rocks and pavement. | Tetramorium caespitum |
| 7b. | Sting simple, clypeus "normal" | 8 |
| | | |
| 8a. | Middle and hind tibial spurs finely pectinate (view at 100x); thorax with modest break between segments, furrows/rugae on sides | Myrmica |
| 8b. | Middle and hind tibial spurs simple or absent. Maxillary palps #5-segments; labial palps # 3 segments | 9 |
| | | |
| 9a. | No spines on propodeum; antennal club with 3 segments | Monomorium |
| 9b. | Spines on propodeum | 10 |
| | | |
| 10a. | Antennal club 3-segmented | 11 |
| 10b. | Antennal club 4-segmented | 12 |
| | | |
| 11a. | Workers dimorphic (large, small); majors (large workers) with huge heads normally with distinct occipital lobes. "Sutures" impressed on rear side of altitrunk | Pheidole |
| 11b. | Workers not dimorphic, head proportions normal | Temnothorax |
| | | |
| 12a. | Antennal scapes short , not reaching occiptal border; eyes small or vestigal; small ants (2.5-4.3mm long) | Stenamma |
| 12b. | Eyes prominent, antennal scapes longer; antennal club prominent, larger ants; clypeus lacking a ridge; thorax with large break between segments | Aphaenogaster |
