Key to Pheidole fallax group

This worker key is based on:

This large assemblage is matched only by the  flavens  group in breadth of geographic distribution. Its species range collectively from the southeastern United States to Argentina, both throughout the mainland and on most of the larger islands of the West Indies. Its signature traits are medium size (with the major Head Width of the great majority of species falling between 1.0 and 2.0 mm), relatively long antennal scapes, sides of the major head subparallel, well-developed mesonotal convexity in both major and minor, dense pilosity, and relatively heavy sculpturing, which includes some rugoreticulation on at least the head of the major.

Two species placed in the fallax group known only from the minor caste, Pheidole aequiseta and Pheidole xanthogaster, cannot be identified with the key to follow. Specimens should be checked directly with the figures and measurements provided in the main section of species diagnoses.

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 * Pheidole
 * "New World Pheidole" Wilson 2003

1

 * Major: seen in full-face view, entire dorsal surface of head, including occipital lobes, covered by carinulae, or rugulae, or rugoreticulum, or some combination of these three types of sculpturing . . . . . 2


 * Major: seen in full-face view, either the occipital lobes and/or much of the rest of the posterior half of the head as well, are free of carinulae, rugae, and rugoreticulum, and are instead either smooth or densely foveolate . . . . . . 25

2
return to couplet #1
 * Major: scape in repose approaches the occipital corner by 2X or less its own maximum width, or reaches it, or exceeds it.. . . . . . 3


 * Major: scape fails to reach the occipital corner by more than 2X its own maximum width . . . . . 12

3
return to couplet #2
 * Major and minor: in side view, propodeal spine at least three-fourths as long as the basal face of the propodeum directly anterior to it (Costa Rica) . . . . . 4


 * Major and minor: in side view, propodeal spine at most one-third as long as the basal face of the propodeum directly anterior to it. . . . . . 5

4
return to couplet #3
 * Major: all of promesonotum covered by parallel transverse carinulae; lower half of mesopleuron covered by parallel longitudinal carinulae; color of body dark brown. Minor: pronotum smooth and shiny . . . . . Pheidole ajax


 * Major: transverse carinulae limited on promesonotum to anterior third of pro no tum, rugulae present on remainder; carinulae absent from mesopleuron; body reddish yellow to dark brown. Minor: most of pro no tum foveolate and opaque . . . . . Pheidole fiorii

5
return to couplet #3
 * Major: rugoreticulum mesad to eye extending all the way posteriorly to the occipital border . . . . . 6


 * Major: rugoreticulum mesad to eye ifpresent limited to space between eye and antennal fossa or at most extending posteriorly two-thirds the way from the eye to the occiput . . . . . 8

6
return to couplet #5 mesonotum (Veracruz, Mexico). . . . . Pheidole confoedusta
 * Major: propodeal spine well developed, its height about equal to its width at the base; in side view the dorsal profile of the petiole fonns a straight line from just behind the spiracle to the summit of the node; transverse carinulae absent from the


 * Major: propodeal spine low and triangular, its height less than its width at the base; in side view the dorsal profile of the petiole is concave, rising from just behind the spiracle to fonn a distinct anterior face of the node; transverse carinulae present on mesonotum . . . . . 7

7
return to couplet #6
 * Major: scape just reaching the occipital corner; only the anterior fourth of the median strip of the first gastral tergite is shagreened and opaque (Santa Catarina, Brazil) . . . . . Pheidole lucretii


 * Major: scape exceeding the occipital corner by more than its own maximum width; all of the median strip of the first gastral tergite shagreened and opaque (Amazonian Peru) . . . . . Pheidole leonina

8
return to couplet #5
 * Trimorphic species, with major, supennajor, and minor castes. Major: dorsal surface of head entirely carinulate, lacking rugoreticulum (supennajor: dorsal half of head with scattered foveae, and lacking carinulae) . . . . . 9


 * Dimorphic species, with no supennajor caste. Major: at least some of the space between the eye and antennal fossa rugoreticulate . . . . . 10

9
return to couplet #8
 * Supermajor: foveae in posterior half of dorsum of head elongate and parallel in direction, their axes oriented longitudinally (southern Arizona through the mountains of western Mexico) (placed in the pilifera group; also keyed out here to ensure identification) . . . . . Pheidole obtusospinosa


 * Supermajor: foveae on posterior half of dorsum of head circular in shape (mountains and high plateaus of central and eastern Mexico) (placed in the pilifera group; also keyed out here to ensure identification) . . . . . Pheidole hirtula

10
return to couplet #8
 * Major: rugoreticulum mesad to the eye extends slightly more than halfway from eye to level of occipital border. Minor: pronotum and posterior half of dorsal surface of head smooth and shiny (Minas Gerais, Brazil) . . . . . Pheidole cardinalis


 * Major: rugoreticulum mesad to the eye limited to space between the eye and antennal fossa. Minor: pronotum and most or all of posterior half of dorsal surface of head foveolate and opaque . . . . . 11

11
return to couplet #10
 * Major: carinulae of dorsal surface of the head sparse, and many of the intercarinular spaces smooth and shiny; some of the hairs on the occiput spatulate. Minor: many of the rather sparse hairs on the dorsal profile of the mesosoma, petiole, and postpetiole are spatulate (Costa Rica) . . . . . Pheidole spathipilosa


 * Major: carinulae on dorsal surface of head dense, with intercarinular spaces all foveolate and opaque. Major and minor: spatulate hairs lacking anywhere on body (Jamaica) . . . . . Pheidole caribbaea

12
return to couplet #2
 * Major: at least the rear third of the dorsum of the head covered by rugoreticulum . . . . . 13


 * Major: at least most of the occiput and often most or all of the rest of the dorsum of the head covered by carinulae, not a rugoreticulum . . . . . 17

13
return to couplet #12
 * Major: humeri anned with prominent angular extensions that extend beyond the margins of the pronotum when viewed from directly above (Panama) . . . . . Pheidole caltrop


 * Major: humeri not armed . . . . . 14

14
return to couplet #13
 * Major: pronotum rugoreticulate (Nicaragua) . . . . . Pheidole gulo


 * Major: pronotum transversely carinulate . . . . . 15

15
return to couplet #14
 * Major: dorsum of head mesad to the eyes and proceeding to a level well in advance of the eyes rugoreticulate; sides of pronotum carinulate. Minor: propodeum with well-developed spine (Argentina, Paraguay, introduced into Gulf Coast of Alabama and Florida) . . . . . . Pheidole obscurithorax


 * Major: areas mesad and anterior to the eyes carinulate only, not rugoreticulate; sides of pronotum carinulate or not. Minor: propodeal spine present or absent . . . . . 16

16
return to couplet #15
 * Major: lower halves of pronotum and mesopleuron and anterior third of side of propodeum transversely carinulate. Minor: lacking propodeal spines; occiput transversely carinulate (Choco, Colombia) . . . . . Pheidole tigris


 * Major: lower halves of mesopleuron and pronotum and anterior third of side of propodeum foveolate only, lacking carinulae. Minor: propodeal spines present; occiput rugoreticulate (Texas) . . . . . Pheidole texana

17
return to couplet #12
 * Major: dorsum of occiput covered by concentric semicircular carinulae that run parallel to the borders of the occipital lobes (Minas Gerais, Brazil) . . . . . Pheidole arcifera


 * Major: dorsum of occiput covered by parallel longitudinal carinulae that do not curve parallel to the occipital lobes . . . . . 18

18
return to couplet #17
 * Major: carinulae originating on the frontal lobes continue unbroken posteriorly to the occipital border . . . . . 19


 * Major: at least some of the carinulae originating on the frontal lobes break up into a rugoreticulum before reaching the occipital border . . . . . 22

19
return to couplet #18
 * Major: in full-face view, profile of entire half of the head posterior to the eyes ringed by a uniform, dense fringe of short, semirecumbent hairs; rugoreticulum on head limited to a very small area (not much greater in extent than the area of the eye) just mesad of the circular carinulae around the antennal fossae (Costa Rica) . . . . . Pheidole mantilla


 * Major: hairs around full-face margin of head posterior to the eyes erect to suberect, very variable in length, not forming a uniform fringe; rugoreticulum at the very least extending from the circular carinulae around the antennal fossae all the way to the eye . . . . . 20

20
return to couplet #19
 * Major: carinulae on the genae (laterad to the eye) extending only halfway from the level of the posterior margin of the eye to the level of the occipital lobes; in dorsal oblique view (mesosoma rotated around long axis 45 degrees from top view), the pronotal profile forms the arc of a circle and is only about as high as the mesonotal convexity behind it. Minor: dorsal surface of head and all of pronotum foveolate and opaque (southwestern U. S., Colorado) (also, check hyatti) . . . . . Pheidole cockerelli


 * Major: carinulae on the genae extend posteriorly all the way to the level of the occipital lobes; in dorsal-oblique view, the pronotal profile bulges upward as a rounded right angle much higher than the mesonotal convexity behind it. Minor: dorsal surface of head and most or all of pro no tum smooth and shiny . . . . . 21

21
return to couplet #20
 * Major and minor: in profile, petiolar node very prominent, its summit running anteriorly through a strong concavity to the peduncle and dropping posteriorly through a nearly vertical face to the postpetiolar junction. Major: in side view, occiput is relatively narrow, and the profile of the posterior half of the dorsal surface of the head just in front of it is straight or nearly so; scape shorter, 0.50-0.59X Head Width. Minor: occiput broader, with the nuchal collar very thin and barely discernible in full-face view (Cuba, Jamaica, Central America, Colombia, Venezuela) . . . . . Pheidole fallax


 * Major and minor: in profile, petiolar node much less distinct, its summit running anteriorly to the peduncle through a shallow convexity and posteriorly through a shallow, oblique convexity to the postpetiolar junction. Major: in side view, occiput broader, with the profile of the posterior half of the dorsum of the head anterior to the occiput moderately convex; scape longer, its length 0.60-0.70 X Head Width. Minor: occiput narrower, with the collar prominent in full-face view (extremely abundant, especially in disturbed environments, through the West Indies and South Americas as far south as northern Argentina) . . . . . Pheidole jelskii

22
return to couplet #18
 * Large species (Head Width of major about 2.0 mm). Major: gena (surface of head laterad to eye) in side view entirely covered by carinulae all the way posteriorly to the occiput . . . . . 23


 * Small species (Head Width of major l.3-l.7 mm). Major: most of gena in side view free of carinulae, instead either densely foveate and opaque or smooth and shiny . . . . . 24

23
return to couplet #22
 * Major and minor: mesopleuron covered by longitudinal carinulae. Major: in full-face view, scape reaching margin of head nearly halfway from level of eye to level of occipital border; propodeal spine in side view narrow, forming a triangle with sides longer than the base (Costa Rica) . . . . . Pheidole hirsuta


 * Major and minor: mesopleuron lacking carinulae. Major: in full-face view, scape reaching margin of head only about one-fourth the distance from the level of eye to level of occipital border; propodeal spine in side view with sides only as long as the base (Brazil) . . . . . Pheidole gigas

24
return to couplet #22
 * Major: pronotal dorsum covered by broken transverse carinulae, and mesopleuron by broken longitudinal carinulae. Minor: dorsal surface of head smooth and shiny; head narrowed posteriorly, with a nuchal collar posterior to the occiput (Amazonian Peru) . . . . . Pheidole tobini


 * Major: pronotal dorsum not carinulate, but with a small patch of rugoreticulum on the humeri; mesopleuron lacking carinulae also. Minor: dorsal surface of head foveolate and opaque, and with scattered longitudinal carinulae; occiput broad, lacking nuchal collar (Arizona) . . . . . Pheidole perpilosa

25
return to couplet #1
 * Major: antennal scapes approach the occipital corners to within 1.5X their own maximum width, reach the corners, or exceed them . . . . . 26


 * Major: antennal scapes fail to reach the occipital corners by 2X or more their own maximum width . . . . . 62