Key to US Aphaenogaster species

This key to the workers of Aphaenogaster of the United States is based on Creighton (1950), Umphrey (1996), Mackay and Mackay (2002) and unpublished notes by Bill Mackay.

1

 * Larger ants, total length usually at least 8 mm; metanotal suture poorly marked on dorsum of mesosoma; propodeal spines long and sharp; most common in arid and semiarid sites => 2
 * Smaller ants, total length rarely over 7 mm; mesopropodeal suture clearly marked on dorsum of mesosoma; propodeal spines often short and poorly developed, may be absent; most common in mesic sites => 4

2

 * Head (excluding mandibles) slightly longer than broad, usually with wavy, longitudinal or transverse rugae extending almost to posterior border, frons usually granulose; common in arroyos and desert canyons => Aphaenogaster albisetosa
 * Head (excluding mandibles) at least 1 ⅓ as long as broad with wavy longitudinal rugae well developed only in anterior half of head; posterior half with feeble rugae which are replaced towards posterior border with fine, coriaceous sculpture; common in open desert => Aphaenogaster cockerelli

4

 * Propodeal spines lacking, or simply represented by small bumps or carinae => 5
 * Propodeal spines present, although may be small => 13

5

 * Base of the antennal scape with a small lobe which projects anteriorly; node of the petiole longitudinally oval when seen from above and scarcely wider than its posterior peduncle => Aphaenogaster floridana
 * Base of the antennal scape without a lobe; node of the petiole almost circular when seen from above and distinctly wider than its posterior peduncle => 11

11

 * Eye very large, strongly protuberant, with 18 to 20 facets in its greatest diameter, its lower border approximately the greatest ocular diameter from the mandibular articulation; body a sorbid, pale, yellowish tan => Aphaenogaster megommata
 * Eye notably smaller, with about 15 facets in its greatest diameter, its lower border about 1½ times the greatest ocular diameter from the mandibular articulation; head and mesosoma ferrugineous red => 12

12

 * Gaster pale brown, same color as mesosoma => Aphaenogaster boulderensis
 * Gaster black, contrasting strongly with brown mesosoma => Aphaenogaster boulderensis smithi

13

 * Antennal scape with a conspicuous lobe which extends rearward along the basal fourth or fifth of the scape => 15
 * Antennal scape without a basal lobe or, if a small lobe is present, it projects forward and does not involve the basal fifth of scape => 16

15

 * Lobe of scape, seen from side, flat and thin, its length usually not more than one-fifth length of scape => Aphaenogaster ashmeadi
 * Lobe of scape, seen from side, thick, its upper face forming obtusely projecting angle in middle, its length usually one-fourth length of scape or longer => Aphaenogaster treatae

16

 * Basal quarter of first gastric tergum with delicate striae which spread fan-wise from attachment of postpetiole => Aphaenogaster mariae
 * Gaster without basal striae, or if present do not spread fan-wise and are limited to basal eighth of tergum => 17

17

 * Outer face of frontal lobe bearing flange which projects rearward in form of tooth or process (caution: small and difficult to see) => Aphaenogaster lamellidens
 * Outer face of frontal lobe without toothed flange => 18

18

 * Postpetiole broader than long and sub oval in shape; propodeal spines longer than basal face of propodeum => Aphaenogaster tennesseensis
 * Postpetiole as long as broad or longer than broad, globular or as truncated cone in shape; propodeal spines shorter than basal face of propodeum => 19

19

 * Antennal scapes of larger workers (not always true of minimums) surpassing occipital margin by an amount equal to, or less than length of first 2 funicular joints => 20
 * Antennal scapes of all workers surpassing occipital margin by amount greater than length of first 2 funicular joints => 23

20

 * Mesopleuron at least in part smooth and shining => Aphaenogaster patruelis
 * Mesopleuron heavily sculptured and opaque => 21

21

 * Head with abundant, fine, punctato-rugose sculpture between longitudinal rugae; color castaneous brown to piceous brown => 22
 * Head with very feeble interrugal sculpture; head and thorax orange yellow, gaster deep brown => Aphaenogaster uinta

22

 * Largest worker 6 mm. in length, female 8 mm. in length; color usually castaneous brown => Aphaenogaster subterranea valida
 * Largest worker 4.5 mm. in length, female 6.5 mm. in length; color usually piceous brown => Aphaenogaster occidentalis

23

 * Middle of the pronotum with very feeble sculpture, its surface strongly shining; propodeal spines very slender => Aphaenogaster flemingi
 * Entire pronotum heavily shagreened or densely sculptured, its surface opaque or subopaque; propodeal spines not notably slender => 24

24

 * Base of antennal scape with small, angular lobe which projects forward => Aphaenogaster huachucana
 * Base of antennal scape without such lobe => 26

26

 * Legs exceptionally long for body size, usually with TL > 1.50 (likely not true for minims, but adjusting for head size, usually with TL > 0.28 + 1.2HW) (rare; restricted to desert regions of southern New Mexico, Arizona, and Texas; reddish brown; cephalic sculpture delicate for size) => Aphaenogaster punctaticeps
 * Legs not exceptionally long for body size, almost always with TL < 1.50 (adjusting for head size, usually with TL < 0.28 + 1.2HW) => 27

27

 * Anterior edge of mesonotum rising abruptly above adjacent portion of pronotum, transverse welt thus formed distinctly concave in middle (more so in medium-sized and larger workers); propodeal spines strongly directed upward => 28
 * Mesonotum not abruptly elevated above pronotum or, if higher (A. picea), anterior edge does not form transverse welt; propodeal spines rarely as long as posterior face of propodeum and usually directed backward => 29

28

 * Eyes relatively larger, maximum diameter twice maximum diameter of scape; propodeal spines at least as long as posterior face of the propodeum; common and widely distributed in mesic habitats => Aphaenogaster fulva
 * Eyes small, maximum diameter only slightly greater than maximum diameter of scape; propodeal spines about ½ length of posterior face of propodeum; known only from Florida, occurring in xeric habitats => Aphaenogaster umphreyi

29

 * Propodeal spines relatively short and legs relatively long, so that ISPL < -0.17 + 0.233TL (see figure below, symbol code N21b); range includes Texas to the mountains of southern Arizona but excludes eastern North America => Aphaenogaster huachucana crinimera, Aphaenogaster texana
 * Propodeal spines relatively longer or legs relatively shorter, so that ISPL > -0.17 + 0.233TL (see figure below, all symbol codes other than N21b); range includes eastern North America but likely excludes the southwestern United States from western Texas to the mountains of southern Arizona => Aphaenogaster carolinensis, Aphaenogaster miamiana, Aphaenogaster picea, Aphaenogaster punctithorax, Aphaenogaster rudis