Key to Pheidole pilifera group

This worker key is based on:

The principal distinguishing feature of this almost exclusively Nearctic assemblage is the possession by the major caste of 0-3 hypostomal teeth, instead of the usual (but not invariable) 4-5 found in other species groups. To this may be added the typically quadrate head shape of both major and minor, as well as their short scapes. Furthermore, the minor of most of the species has proportionally large eyes (the ratio of Eye Length to Head Length among the species ranges from 0.14 to 0.40, with the majority falling 0.20- 0.25, well above the average for other groups). All together these traits allow pilifera-group species to be separated at a glance from unrelated species that also possess 2 or 3 hypostomal teeth, including some members of the Neotropical biconstricta group; Pheidole eidmanni, Pheidole gigas, Pheidole laevivertex, and Pheidole puttemansi of the fallax group: Pheidole nebulosa, Pheidole oaxacana, and Pheidole scabriventris of the flavens group; Pheidole capillata and Pheidole gertrudae of the gertrudae group; Pheidole clydei of the granulata group; and Pheidole fabricator, Pheidole pidax, and Pheidole polita of the tristis group; as well as the African tramp species Pheidole megacephala. The pilifera-group species are otherwise most similar in the totality of their major and minor traits to members of the flavens group.

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 * Pheidole
 * "New World Pheidole" Wilson 2003

1

 * Major: occiput covered partly or entirely by carinulae, rugulae, or a rugoreticulum . . . . . 2


 * Major: occiput smooth and shiny, or sparsely foveate, or densely foveolate, but not bearing carinulae, rugulae, or a rugoreticulum . . . . . 24

2
return to couplet #1
 * Major: rear of head phragmotic, i.e ., occiput strongly concave and rugoreticulate, creating an armored surface (Sinaloa, Mexico) . . . . . Pheidole setsukoae


 * Major: rear of head not phragmotic; occiput convex and variously sculptured . . . . . 3

3
return to couplet #2
 * Major: all or almost all of the dorsal surface of the head carinulate, rugose, foveolate, or combinations thereof . . . . . 4


 * Major: a large portion of the dorsal surface of the head just anterior to the occiput, and including at least a third of the head capsule, smooth and shiny . . . . . 15

4
return to couplet #3
 * A trimorphic species, with heads of both the major and supermajor, including occiput, completely covered with parallel longitudinal carinulae. Very large (Head Width of major 2.5 mm, of supermajor 3.9 mm, and of minor 0.9 mm). Major and minor: propodeal spine in side view exceeding three-fourths the length of the basal face of the propodeum anterior to it (southern Arizona, northern Mexico) . . . . . Pheidole rhea


 * Major: dimorphic, or, if trimorphic, dorsum of head of major partly bare (part of frontal lobes and area behind frontal lobes in obtusospinosa, most of posterior half of head dorsum in tepicana, and clypeus in all three species); smaller than rhea, with Head Width of major 1.0-1.6 mm and of minor 0.5-0.6 mm. Major and minor: propodeal spine in' side view only half the length of the basal face of the propodeum anterior to it . . . . . 5

5
return to couplet #4
 * Major: in side view head "dented"-its profile strongly concave just anterior to the occipital border (southern Texas) . . . . . Pheidole hoplitica


 * Major: in side view, profile smoothly convex, or straight, or at most very weakly concave just anterior to the occipital border . . . . . 6

6
return to couplet #5
 * Major: occiput completely and coarsely rugoreticulate. Minor: posterior half of dorsum of head completely covered by carinulae (Arizona) . . . . . Pheidole cavigenis


 * Major: occiput transversely carinulate or rugulose, lacking rugoreticulum. Minor: posterior half of head foveolate or smooth, not carinulate . . . . . 7

7
return to couplet #6
 * Major: most of the side of the head mesad and posterior to the eye all the way to the occiput is rugoreticulate . . . . . 8


 * Major: side of head mesad and posterior to the eye is smooth or longitudinally carinulate . . . . . 9

8
return to couplet #7
 * Major: smaller (Head Width about 0.90 mm) but with larger eyes (Eye Length about 0.18 mm); medium yellow (some populations of californica, a widespread species of the western U. S.) . . . . . Pheidole californica (in part - also )


 * Major: larger (Head Width about 1.10 mm) but with smaller eyes (Eye Length about 0.14 mm); dark yellow (San Clemente Island, mainland California, and Baja California) . . . . . Pheidole clementensis

9
return to couplet #7
 * A trimorphic species. Major: all of rear half of dorsal surface of head except occiput smooth and shiny. Supermajor: all of rear half of dorsal surface of head carinulate and rugulose. Minor: lower half of mesopleuron and most of the side of propodeum smooth and shiny (Texas and Arizona to central Mexico) . . . . . Pheidole tepicana (in part - also )


 * Dimorphic or trimorphic species. Major: rear half of dorsal surface of head carinulate or rugulose (in supermajor, if present, most of rear half of dorsal surface lacks carinulae or rugulae) . . . . . 10

10
return to couplet #9
 * Major: sides of head posterior to and laterad to the eye mostly or entirely smooth and shiny. Minor: head and pronotum entirely foveolate and opaque . . . . . 11


 * Major: sides of head posterior and laterad to eye foveolate and opaque, or longitudinally carinulate, or both. Minor: head and pronotum entirely smooth and shiny . . . . . 12

11
return to couplet #10
 * Major: in side view, mesonotal convexity well developed, with a front face and descending to metanotal groove in a smooth curve; center of metanotum foveolate and opaque, with irregular, broken carinulae. Minor: longitudinal carinulae present laterad to eye (eastern U. S. populations of pilifera) . . . . . Pheidole pilifera (in part - also )


 * Major: in side view, mesonotal convexity absent; the promesonotum as a whole presents a continuous profile that descends to the metanotal groove in a steep posterior face. Minor: carinulae absent laterad to the eye (Chihuahua, Mexico) . . . . . Pheidole torosa

12
return to couplet #10
 * Trimorphic species, with occiput of major longitudinally carinulate . . . . . 13


 * Dimorphic species, with occiput of major transversely carinulate . . . . . 14

13
return to couplet #12
 * Occiput of supermajor in full-face view sparsely covered by round foveae, with interspaces smooth and shiny (upland central Mexico) . . . . . Pheidole obtusospinosa (in part - also ))


 * Occiput of supermajor in full-face view sparsely covered by elongate foveae, with interspaces densely foveolate and opaque (montane southern Arizona, western Mexico) . . . . . Pheidole obtusospinosa (in part - also )

14
return to couplet #12
 * Major: center of promesonotal dorsum smooth and shiny. Minor: hairs on dorsa of mesosoma and petiole ordinary, not clavate. Major and minor: yellow (Arizona, southern California) . . . . . Pheidole micula


 * Major: center of promesonotum foveolate and opaque. Minor: most of the hairs on the dorsa of mesosoma clavate. Major and minor: light brown (Mississippi to southwestern U. S. and northern Mexico) . . . . . Pheidole soritis

15
return to couplet #3
 * Major: all of side of pronotum and upper half of sides of mesopleuron and propodeum covered by longitudinal carinulae; summit of petiolar node in side view acuteangular; seen from above, petiolar node drawn laterally into sharp points. Minor: posterior half of head carinulate (Colorado, New Mexico, Arizona) . . . . . Pheidole senex


 * Major: areas of body listed above lacking carinulae; summit of petiolar node in side view rounded; seen from above, the sides of the petiolar node either rounded or angular. Minor: posterior half of head not carinulate . . . . . 16

16
return to couplet #15
 * Major and minor: promesonotal profile seen from dorsal-oblique view (mesosoma rotated around long axis for 45 degrees from top view), with 3 convexities, 2 pronotal and a single mesonotal one, with the central convexity (second pronotal) being by far the highest. Minor: in full-face view, the occipital margin deeply concave, the two halves meeting to form an angle at midline; the eye enormous, as long as the entire petiole (Baja California Sur) . . . . . Pheidole bajaensis


 * Major and minor: promesonotal profile seen from dorsal-oblique view, with one or 2 convexities, or if 3, the central convexity is only about as high as the first convexity. Minor: in full face view the occipital margin variable, usually only shallowly concave and not forming an angle at midline; eye shorter than petiole . . . . . 17

17
return to couplet #16
 * Major: seen from dorsal-oblique view, pronotum is drawn out into a large, equilaterally triangular lobe that projects far above the level of the mesonotal convexity (central Mexico) . . . . . 18


 * Major: seen from dorsal-oblique view, the pronotum is not extended as a large triangular lobe; instead the promesonotal border forms a single, continuous convexity only slightly higher than the level of the mesonotal convexity . . . . . 19

18
return to couplet #17
 * A trimorphic species, with major, supermajor, and minor castes. Major: postpetiolar node seen from above drawn laterally into blunt right angles. Minor: entire dorsum of pronotum foveolate and punctate; carinulae of frontal lobes extend posteriorly beyond level of eye . . . . . Pheidole polymorpha


 * Dimorphic so far as known (from small type series) but supermajor may exist. Major: postpetiolar node tapered laterally to form points. Minor: dorsum of pronotum smooth and shiny . . . . . Pheidole calens

19
return to couplet #17
 * Major: seen from the side, profile of posterior half of dorsum of head flat to very slightly concave; mesonotum partly to wholly foveolate, anterior fringe of first gastral tergite shagreened. Minor: posterior half of dorsal surface of head partly or entirely foveolate (western populations of pilifera) . . . . . Pheidole pilifera (in part - also )


 * Major: seen from the side, posterior half of dorsum of head weakly to moderately convex; mesonotum entirely smooth and shiny; all of first gastral tergite smooth and shiny. Minor: posterior half of dorsal surface of head entirely smooth and shiny . . . . . 20

20
return to couplet #19
 * Minor (note, not major): dorsal margin of petiolar node, seen from the rear, concave. The following traits are typical but not certainly diagnostic. Major: viewed from the side, occiput flattened, its profile only very weakly convex and its width from front to back over 1.5 X the width of the anterior margin of the side of the head; seen from above, sides of postpetiolar node drawn into acute angles; in full-face view, occipital lobes sub angular, their inner margins running mesad to the midline of the head in nearly straight lines. Minor: seen from above, postpetiolar node trapezoidal in shape (Oregon, Nevada, northern California) . . . . . Pheidole creightoni


 * Minor (note, not major): dorsal margin of petiolar node, seen from the rear, straight or convex. The following traits are typical but not certainly diagnostic. Major: viewed from side, occiput strongly convex, its width from front to back only about as great as the width of the anterior margin of head; seen from above, postpetiolar node oval in shape, with rounded or sub angular lateral margins; in full-face view, occipital lobes arc-shaped, their inner margins running mesad to the midline of the head in convex lines. Minor: seen from above, postpetiolar node circular or oval in outline . . . . . 21

21
return to couplet #20
 * Major: no longitudinal carinulae occur directly posterior to the frontal triangle, and no carinulae at all extend posteriorly beyond the eye for a distance as great as the length of the eye. Minor: dorsal margin of pronotum seen in profile lined by a small number of spatulate hairs. Major and minor: medium yellow (southern Texas) . . . . . Pheidole aurea


 * Major: longitudinal carinulae occur behind the frontal triangle; and carinulae mesad to the eye extend past the eye for a distance equal to the length of the eye or more. Minor: hairs on pronotal dorsum are tapered or blunt-tipped, not spatulate. Major and minor: brownish to reddish yellow or light brown . . . . . 22

22
return to couplet #21
 * Trimorphic, with minor, major, and supermajor. Major: carinulae originating from directly behind the frontal triangle reach less than halfway to the occipital border. Minor: eye only as long as its distance to anterior border of head . . . . . Pheidole tepicana (in part - also )


 * Dimorphic, with minor and major only. Major: carinulae originating from directly behind the frontal triangle reach three-fourths of the way to the occipital border. Minor: eye longer than its distance to anterior border of head . . . . . 23

23
return to couplet #22
 * Major: pronotum foveolate and opaque, with transverse carinulae present in addition on the anterior quarter of its dorsum. Maj or light reddish brown, minor yellowish brown (Texas to Arizona) . . . . . Pheidole rugulosa


 * Major: pronotum completely smooth and shiny, with no carinulae. Major and minor: yellow (some populations of californica, found from northern California north to Washington and east to Nevada) (also, check against clementensis, especially with reference to size, Eye Length, and color) . . . . . Pheidole californica (in part - also )

24
return to couplet #1
 * Major and minor: propodeal spine absent; in side view basal and descending faces run together as an unbroken convexity or obtuse angle. Minor: head with psammophore, comprising hairs on the ventral surface of the head more than 2 X longer than most on the dorsal surface of the head, plus clypeal hairs that extend anteriorly well beyond the closed mandibles (Arizona to southern California) . . . . . Pheidole barbata


 * Major and minor: propodeal spine present, at least as a right-angular projection; psammophore and elongated clypeal hairs present or not . . . . . 25

25
return to couplet #24
 * Major: in side view, lower margin of postpetiole bears a prominent toothlike or right-angular projection . . . . . 26


 * Major: in side view, lower margin of postpetiole straight or slightly convex, lacking a toothlike or angular projection . . . . . 28

26
return to couplet #25
 * Major: subpostpetiolar projection right-angular; occiput covered with scattered conspicuous foveae, and rest of dorsum of head anterior to the occiput longitudinally carinulate; promesonotum partly covered by rugoreticulum (Florida) . . . . . Pheidole littoralis


 * Major: postpetiolar projection acute, toothlike; occiput, rest of dorsum of head posterior to level of eyes, and promesonotum smooth and shiny . . . . . 27

27
return to couplet #26
 * Very large species (Head Width of major 2.7 mm, of minor 0.8 mm). Major: postpetiolar node with prominent transverse carina across its middle, and with angulate corners. Minor: in side view, peduncle of petiole anterior to the node of typical length, i.e., only about as long as the postpetiole, and with a well-developed node (Arizona, New Mexico) . . . . . Pheidole militicida


 * Medium-sized species (Head Width of major 1.6 mm, of minor 0.5 mm); postpetiole oval, and lacking a transverse carina. Minor: in side view, petiole extremely long and thin, its peduncle twice the length of the postpetiole and with a flattened, barely discernible node (southern California, Arizona, northern Mexico) . . . . . Pheidole psammophila

28
return to couplet #25
 * Major: space between eye and antennal fossa rugoreticulate . . . . . 29


 * Major: space between eye and antennal fossa longitudinally carinulate only (supermajor, if present, rugoreticulate in this space) . . . . . 31

29
return to couplet #28
 * Major: occiput mostly smooth and shiny; first gastral tergite entirely smooth and shiny. Minor: propodeal spine reduced to denticle (Mexico City) . . . . . Pheidole azteca


 * Major: occiput and anterior half of first gastral tergite foveolate and opaque. Minor: propodeal spine strongly developed . . . . . 30

30
return to couplet #29
 * Major: carinulae just mesad to eye extend beyond eye less than the length of the eye. Minor: in side view, propodeal spine longer than the basal face anterior to it (Oaxaca, Mexico) (placed in the flavens group; also keyed out here to ensure identification) . . . . . Pheidole oaxacana


 * Major: carinulae just mesad to eye extends beyond eye by 3 X length of eye or more. Minor: in side view, propodeal spine only about one-fourth the length of the basal face of the propodeum anterior to it (Veracruz, Mexico) (placed in the flavens group; also keyed out here to ensure identification) . . . . . Pheidole scabriventris (=Pheidole nebulosa)

31
return to couplet #28
 * Major: entire side of mesosoma (pronotum, mesopleuron, and propodeum) covered by parallel longitudinal carinulae . . . . . 32


 * Major: at least the mesopleuron and usually most of the rest of the side of the pronotum free of carinulae . . . . . 33

32
return to couplet #31
 * Major: pronotal dorsum covered by transverse carinulae and mesonotal dorsum by longitudinal carinulae on a surface made opaque by foveolae; hypostoma with 3 teeth. Minor: pronotum foveolate and opaque (east-central u. S., northeastern Mexico) . . . . . Pheidole davisi


 * Major: promesonotal dorsum smooth and shiny; hypostoma lacking teeth completely. Minor: pronotum smooth and shiny (Florida) . . . . . Pheidole adrianoi

33
return to couplet #31
 * Major: occiput covered by widely spaced, conspicuous foveae . . . . . 34


 * Major: occiput lacking a field of conspicuous foveae . . . . . 35

34
return to couplet #33
 * Major and minor: propodeal spines reduced to protruding right angles (Yucatan, Mexico) . . . . . Pheidole yucatana


 * Major and minor: propodeal spines well developed, with acute-angular apices (Baja California) . . . . . Pheidole macrops (in part - also )

35
return to couplet #33
 * Major: pronotal dorsum covered by transverse carinulae or rugulae . . . . . 36


 * Major: pronotal dorsum possessing at most one or 2 patches of carinulae . . . . . 38

36
return to couplet #35
 * Major: mesonotum covered by longitudinal carinulae; many of the carinulae of the frontal lobes attain the occipital border; in dorsal-oblique view, profile of humerus subangulate and most of profile of promesonotum posterior to it flat (northern Florida) . . . . . Pheidole carrolli


 * Major: mesonotum with at most several transverse carinulae; carinulae of frontal lobes fail to reach occipital border; in dorsal-oblique view, profile of humerus and rest of promesonotum convex . . . . . 37

37
return to couplet #36
 * Major: large, Head Width about 2.0 mm. Minor: dorsal surface of head completely covered by carinulae; Eye Length much smaller than distance from eye to anterior border of head (Texas, Arizona) . . . . . Pheidole virago


 * Major: smaller, Head Width about 1.3 mm. Minor: dorsal surface of head mostly free of carinulae; eye very large, Eye Length much greater than distance from eye to anterior border of head (“subsp. tucsonica” of xerophila, a widespread species in southwestern U. S., California, and Sonora, Mexico) . . . . . Pheidole xerophila (in part - also )

38
return to couplet #35
 * Major: in full-face view, tip of scape touched to margin of head is OAX or more the distance from level of posterior margin of eye to level of occiput . . . . . 39


 * Major: in full- face view, tip of scape touched to margin of head is less than OAX the distance from level of posterior margin of eye to level of occiput . . . . . 43

39
return to couplet #38
 * Dimorphic species, with major and minor castes only. Major: in full-face view, posterior third of dorsum of head foveolate or smooth, lacking longitudinal carinulae . . . . . 40


 * Trimorphic species, with major, supermajor, and minor. Major: in full -face view, posterior third of head completely covered by parallel longitudinal carinulae . . . . . 42

40
return to couplet #39
 * Major: in side view, mesonotal convexity well developed, with a distinct anterior face separating it from the pronotal profile in front and a distinct posterior face separating it from the metanotal groove to the rear; head brownish yellow anterior to the eyes and reddish brown behind (Texas to Arizona, northern Mexico) (placed in the fallax group; also keyed out here to ensure identification) . . . . . Pheidole sciophila


 * Major: in side view, mesonotal convexity absent, with promesonotal profile forming a single semicircular curve; head concolorous yellow or tricolored, with dark band across the middle of the head . . . . . 41

41
return to couplet #40
 * Major: dorsal surface of head concolorous yellow; pilosity very sparse, with about a dozen hairs fringing the dorsal profile of the head capsule and only several fringing the entire mesosomal profile (Guatemala) . . . . . Pheidole defecta (known only from the major)


 * Major: head colored to create a unique "mask," with the dorsal surface of the occipital lobes and the genae yellow and the rest of the dorsal surface of the head brown; abundant hairs line the dorsal profiles of the head capsule and mesosoma (Costa Rica) (placed in the flavens group; also keyed out here to ensure identification) . . . . . Pheidole nasutoides

42
return to couplet #39
 * Supermajor: foveae on posterior third of head, including occiput, longitudinally elongate (mountains of southern Arizona and western Mexico) (formerly subdentata) . . . . . Pheidole obtusospinosa (in part - also )


 * Supermajor: foveae on posterior third of head, including occiput, circular in shape (high plateaus and mountains of eastern and central Mexico) . . . . . Pheidole obtusospinosa (in part - also )

43
return to couplet #38
 * Major: side of petiole with longitudinal carinulae; dorsum of postpetiolar node foveolate, opaque, and transversely carinulate. A large (Head Width of major 1.9 mm, of minor 0.9 mm), reddish brown species (Texas, Arizona, western Mexico) . . . . . Pheidole titanis


 * Major: petiole and postpetiole lacking carinulae; dorsum of postpetiolar node smooth and shining. Size variable, but usually much smaller, color variable . . . . . 44

44
return to couplet #43
 * Combining the following two traits: first, in major, longitudinal carinulae of frontal lobes do not extend posteriorly past level of posterior margin of eye, and, second, in side view the promesonotal profile of the major and minor forms a near-perfect semicircle, without any trace of a separate mesonotal convexity . . . . . 45


 * Either the longitudinal carinulae of the frontal lobes of the major extend posteriorly beyond the level of the posterior margin of the eye by a distance at least as great as the length of the eye, or else the promesonotal profile of the major and minor is irregular, usually with a discernible mesonotal convexity or a sharp drop of the mesonotum posteriorly to the metanotal groove, or both . . . . . 48

45
return to couplet #44
 * Major: almost all of the sides of the pronotum lined with curving longitudinal carinulae (southern Arizona, California) . . . . . Pheidole gilvescens (in part - also )


 * Major: at most, the lower anterior part of the sides of the pronotum lined with several longitudinal carinulae . . . . . 46

46
return to couplet #45
 * Major: seen from above, lateral margins of postpetiolar node drawn into sharp, hornlike angles; seen in dorsal-oblique view (mesosoma rotated around long axis 45 degrees from top view), humerus protrudes as an obtuse angle. Minor: seen from above and obliquely, humerus of minor surmounted by a low denticle. Reddish brown; in addition, major has a circular dark brown spot in center of dorsum of the head capsule (Texas, northern Mexico) . . . . . Pheidole pinealis


 * Major: seen from above, postpetiolar node oval or trapezoidal in shape; seen in dorsal-oblique view, humerus of major and minor smoothly convex. Yellow; major lacks a spot on center of head capsule . . . . . 47

47
return to couplet #46
 * Major: postpetiolar node viewed from above trapezoidal; pronotum lacking carinulae; propodeal spine viewed from the side only about as long as propodeal spiracle. Minor: eye much longer than the distance from its anterior border to the genal border (Nevada, southern California) . . . . . Pheidole paiute (in part - also )


 * Major: postpetiolar node viewed from above oval; propodeal spine viewed from the side 3 X longer than the propodeal spiracle is wide. Minor: eye only about as long as the distance from its anterior border to the genal border (montane Chiapas, Mexico) . . . . . Pheidole agricola

48
return to couplet #44
 * Major: lateral margins of postpetiolar node drawn out into sharp spines; postpetiolar node 2 X as wide as petiolar node . . . . . 49


 * Major: postpetiolar node oval, semicircular, conulate, or acute-angular, not spinose, and less than 2 X as wide as petiolar node . . . . . 50

49
return to couplet #48
 * Major: in side view, petiolar node is pointed at summit; sides of propodeum, petiole, and postpetiole smooth and shiny. Large size (Head Width of major 1.7 mm, of minor 0.5 mm) (southern Arizona, northern Mexico) . . . . . Pheidole spadonia


 * Major: in side view, petiole is rounded at summit; sides of propodeum, petiole, and postpetiole foveolate and opaque. A smaller species (Head Width of major 1.1 mm, of minor 0.5 mm) (southwestern U. S., California, northern Mexico) . . . . . Pheidole cerebrosior

50
return to couplet #48
 * Major: seen in dorsal-oblique view (mesosoma rotated around long axis 45 degrees from top view), humerus swollen into a blunt tooth or prominent lobe that rises in outline well above the posterior contour of the rest of the pronotum . . . . . 51


 * Major: seen in dorsal-oblique view, profile of humerus does not rise high above the posterior profile of the rest of the pronotum but forms a more or less even line with it . . . . . 53

51
return to couplet #50
 * Trimorphic species, with major, supermajor, and minor castes. Major: postpetiolar node, viewed from above, forming a half-circle in outline, with broad side of the semicircle at the posterior margin; lower half of mesopleuron smooth and shiny. Minor: head in full-face view square-shaped, about as wide as long; in side view postpetiolar node very low, its summit profile a feeble convexity (southern Texas, Arizona) . . . . . Pheidole macclendoni


 * Dimorphic or trimorphic species. Major: postpetiolar node viewed from above centrally oval in outline and with angulate or subangulate sides; lower half of mesopleuron either smooth and shiny or foveolate and opaque. Minor: head in full-face view rectangular, distinctly longer than wide; in side view, postpetiolar node well developed, its summit profile forming a strong convexity . . . . . 52

52
return to couplet #51
 * Trimorphic species, with major, supermajor, and minor castes. Major: no longitudinal carinae arising from directly behind the frontal triangle, and thus there is a gap along the midline of the head between the carinulae arising on either side from the frontal lobes. Minor: seen from above and obliquely, the humerus lacks any protrusion, so that the promesonotal profile forms a single smoothly curving line (central and southern Mexico) . . . . . Pheidole centeotl


 * Dimorphic species, supermajor lacking. Major: longitudinal carinulae arise from behind the frontal triangle and continue along the midline of the head to more than halfway between the level of the posterior margin of the eye and the occipital border. Minor: seen from above and obliquely, the profile of humerus is broken by a distinct denticle or lobe (cold temperate U. S., New York to California) . . . . . Pheidole bicarinata

53
return to couplet #50
 * Major: most of the longitudinal carinulae on the frontal lobes extend beyond the level of the eyes to at least midway between the level of the posterior margin of the eyes and the occipital margin; blackish brown, with contrasting brownish yellow clypeus. Minor: blackish brown, including clypeus (mountains, Colorado to Texas and Arizona) . . . . . Pheidole ceres


 * Major: longitudinal carinulae of frontal lobes extend beyond the eyes by less than the length of the eyes, or not at all, although several carinulae in between, along the midline of the head, may extend farther; color among species varies from yellow to blackish brown . . . . . 54

54
return to couplet #53
 * Major: several carinulae originating from behind the frontal triangle extend along the dorsal midline of the head all the way to the occiput. A very small species (Head Width of major 0.9 mm, of minor 0.4 mm), yellow in color. Minor: in side view, pilosity along dorsal profile of promesonotum consists of 4 evenly spaced pairs of clavate hairs (Texas) . . . . . Pheidole marcidula


 * Major: carinulae originating from above the frontal triangle extend along midline of head at most halfway between eyes and occiput. Larger species (Head Width of major 1.1-1.3 mm, of minor 0.5-0.6 mm), of various colors. Minor: pilosity on dorsal promesonotal profile not arrayed in evenly spaced pairs, and not clavate . . . . . 55

55
return to couplet #54
 * Major: pronotum completely lacks transverse carinulae; several carinulae originating behind frontal triangle extend along midline of dorsum of head to midway between the level of the posterior margin of the eyes and the occipital border; posterior half of the dorsum of the head bearing widely spaced, conspicuous foveae (Baja California) . . . . Pheidole macrops (in part - also )


 * Major: pronotum bears transverse carinulae on its anterior half; carinulae originating behind frontal triangle extend only slightly beyond the level of the posterior margins of the eyes; posterior margin of the dorsum of the head lacking foveae . . . . . 56

56
return to couplet #55
 * Major: in side view, posterior half of dorsal profile of head is smoothly convex, and entire head is not tapered from mid-level to the occiput . . . . . 57


 * Major: in side view, posterior half of dorsal profile of head is flat or nearly so, and entire head tapers in side view from mid-level to the occiput . . . . . 58

57
return to couplet #56
 * Major: larger, Head Width about 1.20 mm. Minor: eye proportionately much larger, with Head Width about 0.50 mm and Eye Length 0.16 mm (southern California, Baja California) . . . . Pheidole yaqui


 * Major: smaller, Head Width about 1.04 mm. Minor: eye proportionately smaller, with Head Width about 0.5 mm and Eye Length 0.12 mm (Nevada, southern California) . . . . Pheidole paiute (in part - also )

58
return to couplet #56
 * Major: yellow; postpetiolar node seen from above transversely oval in shape, only about a third wider than the petiolar node; sides of pronotum carinulate. Minor: yellow (southern Arizona to California) . . . . Pheidole gilvescens (in part - also )


 * Major: reddish brown; postpetiolar node transversely conulate, nearly 2 X wider than the petiolar node; sides of pronotum mostly smooth. Minor: yellowish brown. (“Typical form” of xerophila, a widespread species in southwestern U. S., California, and Sonora, Mexico) . . . . . Pheidole xerophila (in part - also )