Key to New World Pheidole Species Groups

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This worker key is based on: Wilson, E. O. 2003. Pheidole in the New World: A dominant, hyperdiverse ant genus. Harvard University Press, Cambridge, MA.

Key to the Species Groups of the Nonparasitic New World Pheidole, Based on the Worker Castes

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1

  • Antenna 10-or 11-segmented; very small Neotropical species (Head Width of major 0.5-0.7 mm) . . . . . 2
  • Antenna 12-segmented; size usually larger than 0.7 mm . . . . . 3

2

return to couplet #1

3

return to couplet #1

  • Antennal club 4-segmented; Head Width of major 1.2 mm or more (Nearctic and West Indian) . . . . . Pheidole granulata group
  • Antennal club 3-segmented; Head Width of major variable . . . . . 4

4

return to couplet #3

  • Head of major with deep scrobes within which the entire antennae can be folded; in addition, the frontal lobes are often expanded laterally so as to cover and hide the folded antennae . . . . . 5
  • Head of major either lacks antennal scrobes or else scrobes are present but too shallow to receive the entire folded antennae; also, the frontal lobes are never expanded enough to cover the folded antennae . . . . . 6

5

return to couplet #4

  • Occiput in full-face view with one or more transverse carinae across its dorsum, which often demarcate the dorsum as a section distinct from the rest of the dorsal head surface (mostly Argentina, ranging to southern Brazil and Ecuador, but one species reaching Trinidad) (also, scan Pheidole scrobifera group) . . . . . Pheidole aberrans group
  • Occiput in full-face view lacking transverse carinae across its dorsum, which is usually rugoreticulate and occasionally longitudinally carinulate or smooth (widespread, Central and tropical South America) . . . . . Pheidole scrobifera group

6

return to couplet #4

  • Entire central half of dorsal profile of major head "scooped out" (deeply concave to create a large semicircle in lateral profile) yielding in side view a twisted overall head shape (South America) . . . . . Pheidole distorta group
  • Dorsal center of head of major in side view with at most a weak concavity, insufficient to alter the essentially oval shape of the head in side view, or else the concavity covers less than half the dorsal profile of the head and is located on the posterior half of the head just anterior to the occiput . . . . . 7

7

return to couplet #6

  • Most or all of the dorsal surface of the posterior half of the head capsule of the major covered by a longitudinal row of prominent transverse carinae that form a ladder-like pattern. Head Width of major only 0.6- 0.9 mm (Neotropical; also, scan Pheidole tachigaliae group, which species are outwardly similar but have 11-segmented antennae) . . . . . Pheidole transversostriata group
  • Dorsal surface of the head of the major lacks a ladder-like array of transverse carinae or else, rarely, such an array exists but then the major is much larger, with Head Width over 1.1 mm (see Pheidole arietans of Pheidole tristis group) . . . . . 8

8

return to couplet #7

  • Head of major anteriorly phragmotic (anterior dorsal surface flattened and joining the posterior dorsal surface at a distinct, obtuse angle); dorsal surface of major head mostly or entirely foveolate or rugoreticulate, and opaque (southern United States to northern South America) . . . . . Pheidole lamia group

9

return to couplet #8

  • Metanotum of major, and not just its pronotum and mesonotum, long and convex in side view; as a consequence, the profile of the major's mesosoma in dorsal-oblique view (mesosoma rotated around long axis 45 degrees) has 4 convexities approximately equal in size (2 on the pronotum and one each on the mesonotum and metanotum) (represented in the New World by only one species, indica, of Mediterranean origin, recorded from several widely scattered localities) . . . . . Pheidole teneriffana group (=Pheidole indica)
  • Metanotum of major always very short, usually indistinct in side view, and rarely convex; as a consequence, profile of major's mesosoma in dorsal-oblique view has at most 3 convexities, whether equal in size or not . . . . . 10

10

return to couplet #9

  • Hypostomal border of major bearing only 2 or 3 teeth (one on each side of ventral midline of head, and 0 or one on the midline), or else no teeth at all. (A small number of species exiting here will also later exit from couplet 13 into couplet 14 and thus join the species exiting from the lower lug of couplet 10. This necessary maneuver has no effect on the flow of the key overall.) . . . . . 11
  • Hypostomal border of major bearing 4-5 teeth (one pair each laterad to the ventral midline of the head and 0 or one on the midline) . . . . . 14

11

return to couplet #10

  • Possessing all of the following traits. Large species (Head Width of major 1.4-1.9 mm). Major: mesonotum in side view forming a strong, usually symmetrical convexity; ventral margin of post petiole in side view very weakly convex, straight, or weakly concave, and lacking a lobe or spine; head in full -face view heart-shaped; outline of head in full face bare of pilosity (exception: Pheidole simplex). Minor: head narrowed posteriorly, with a nuchal collar (Central and South America) (if difficulty is encountered, also scan Pheidole diligens group and Pheidole fallax group) . . . . . Pheidole biconstricta group (in part - also #20)
  • Possessing one or more of the following traits. Major: Head Width less than 1.4 mm or more than 2.0 mm; mesonotum with weak or asymmetrical convexity, or no convexity at all; ventral margin of postpetiole in side view moderately to strongly convex, or with a lobe or spine; head in full-face view roughly quadrate or rectangular; outline of head in full face fringed by hairs. Minor: occiput broad, lacking nuchal collar CU. S., Mexico; plus one widespread tropical tramp species, Pheidole megacephala, in disturbed habitats) . . . . . 12

12

return to couplet #11

  • Possessing all of the following traits. Major and minor: in side view, entire postpetiole oval in shape, with all of the ventral margin bulging downward in a conspicuous convexity, the node low and weakly developed; mesonotal convexity absent, the promesonotal profile in side view forming a smooth, continuous convex line like the arc of a circle; color brownish yellow. Major: outline of head plus mandibles in full-face view forms a near-perfect heart shape; rugoreticulum present between eye and antennal fossa. Minor: occiput broad, lacking an occipital collar. (Occurs in disturbed habitats through much of tropical America, including southern Florida and Bermuda) . . . . . Pheidole megacephala group =(Pheidole megacephala)
  • Possessing one or more of the following traits. Major and minor: postpetiole either roughly circular, semicircular, or irregular in profile, not oval, the node strongly developed, and the ventral margin as a whole not forming a conspicuous convexity; mesonotal convexity present; color yellow, brown, with or without reddish tinge, of various mixes and shades, but not brownish yellow. Major: outline of head together with mandibles in full-face view not heart-shaped, but roughly quadrate or rectangular; rugoreticulum absent between eye and antennal fossa. Minor: occiput narrow, with a nuchal collar . . . . . 13

13

return to couplet #12

  • Along with the bidentate or toothless hypostoma of the major, the major and minor have a roughly quadrate or short-rectangular head shape; i.e., in full-face view, the lateral margins of the head are straight to weakly curved, and the head capsule is as wide or almost as wide as it is long. Minor: eyes large compared to head size, the ratio of Eye Length to Head Length is 0.14 to 0.40, with the majority of species 0.20-0.25 (D. S. and Mexico, with only a few species known from south of the Mexican Plateau) . . . . . Pheidole pilifera group
  • Either the major and minor have moderately to strongly curving sides of head; or the ratio of Eye Length to Head Length in the minor is 0.15 or less; or both of these traits are present (exception: Pheidole capillata, placed in Pheidole gertrudae group on overall habitus, q.v.) . . . . . 14

14

return to couplet #10; return to couplet #13

  • Possessing all of the following traits. Large species (Head Width of major 1.2- 1.6 mm); scape of major conspicuously flattened near its base, its greatest width there equal or almost equal to or greater than its maximum width at transects along the distal (outer) half; petiolar peduncle and node of major thick; head of major strongly heart-shaped, with deep mid-occipital cleft and rounded sides in full-face view; minor with broad occiput in frontal view, lacking a nuchal collar (southern D. S. and Mexican Plateau) (if difficulty is encountered, also scan Pheidole diligens group and Pheidole fallax group) . . . . . Pheidole crassicornis group
  • Possessing one or more of the following traits. Major either small to medium-sized (Head Width less than 1.2 mm) or very large (Head Width greater than 1.6 mm); scape much narrower at its basal segment than at its distal segment; petiolar peduncle and node of major slender; head of major roughly quadrate or rectangular, with a relatively shallow occipital cleft and straight to weakly convex sides in full-face view; minor with narrowed occiput and nuchal collar . . . . . 15

15

return to couplet #14

  • Possessing all of the following traits. Major and minor: propodeal spine absent or at least reduced to a short, wide angle or denticle; mesonotal convexity absent; propodeal spiracle conspicuously large, its greatest width equal to or greater than the distance between its dorsal border and the dorsal border of the propodeum in side view; medium to large (Head Width of major 1.1-1.6 mm) (Brazil, Peru) (if difficulty is encountered, also scan Pheidole diligens group) . . . . . Pheidole gertrudae group
  • Possessing one or more of the following traits. Major and/or minor: propodeal spine well developed; mesonotal convexity present, with front and rear faces distinct in side view; propodeal spiracle small to medium in size, its greatest width less than the distance between its dorsal border and the dorsal border of the propodeum in side view; either small (Head Width of major less than 1.1 mm) or very large (Head Width of major greater than 1.6 mm) . . . . . 16

16

return to couplet #15

  • Possessing all of the following traits. Small species (Head Width of major 0.7-l.0 mm); slender body form; major with medium to long antennal scape, such that when the tip of the scape is touched to the lateral border of the head in full-face view, it reaches halfway between the eye and occipital corner, or farther; antennal scape of the minor moderately long, so that when laid across the occipital corner, the scape in full-face view exceeds the corner by at least 4X the maximum scape width; head of minor roughly quadrate or rectangular, sometimes narrowing at occiput, its posterior dorsal half completely foveolate and opaque, with no other sculpturing except, at most, short carinulae on the antennal fossa (Mexico, Central America, northern South America) (close to Pheidole flavens group, which should also be scanned if difficulty is encountered) . . . . . Pheidole punctatissima group
  • Possessing one or more of the following traits. Medium-sized to large species (Head Width of major over l.0 mm); robust body form; majors with short antennal scape, its tip failing to reach as far as halfway between the eye and occipital corner; antennal scape of the minor short, so that when laid toward the occipital corner, the scape of the minor in full-face view exceeds the corner by less than 4X the maximum scape width; head of minor variously shaped, but neither quadrate nor rectangular; its posterior dorsal half smooth and shiny, carinulate, rugulose, or rugoreticulate; posterior half of head of dorsum of minor smooth and shiny, carinulate, or rugoreticulate, but not exclusively foveolate . . . . . 17

17

return to couplet #16

  • Possessing all of the following traits. Medium to very small (Head Width of major 1.2 mm or less, and in the great majority of species 1.0 mm or less); robust body form; mesonotal convexity in side view absent or at most vestigial, so that the profile of the promesonotum is continuous and descends to the metanotal groove either in a smooth curve or else abruptly through an obtuse angle (exception: meinertopsis, q.v., has a developed mesonotal convexity); antennal club thick compared with other segments of the funiculus; scape short, that of major extending at most slightly beyond the midpoint between the eye and occipital corner, and that of minor at most only slightly more than 2X its maximum width beyond the occipital corner (very abundant and diverse from U. S. to Argentina) (if difficulty is encountered, also scan Pheidole pilifera group, Pheidole punctatissima group, and Pheidole tristis group, and in the latter especially, the flavens-to-tristis intermediate “Pheidole carapuna complex,” comprising Pheidole boltoni, Pheidole carapuna, Pheidole cuprina, and Pheidole tristicula) . . . . . Pheidole flavens group
  • Possessing one or more of the following traits. Medium to large (Head Width of major more than 1.2 mm); slender body form; mesonotal convexity in side view present, with defined anterior and posterior faces; antennal club only slightly thicker than remainder of funiculus; scape of major extending well beyond the midpoint between eye and occipital corner, and scape of minor by 4X or more its maximum width beyond the occipital corner . . . . . 18

18

return to couplet #17

  • Mesonotal convexity viewed from the side weakly developed or absent. Also, in most of the species the antennal scape of the major is very short, so that when the tip is touched to the lateral margin of the head in full-face view it reaches much less than half the distance from the eye to the occipital corner; in many of the species also, the frontal lobes or median clypeal carina of the major are extended prominently forward as angles, horns, or spikes (exclusively Neotropical, with most species South American and West Indian) (if difficulty is encountered, also scan Pheidole flavens group and Pheidole diligens group) . . . . . Pheidole tristis group
  • Mesonotal convexity almost always strongly developed, rarely low and weak and never absent, always with clearly defined anterior and posterior faces: antennal scape of major usually reaches well beyond the midpoint between the eye and occipital lobe, seldom only to the midpoint; neither frontal lobes nor median clypeal carina of the major project forward in side view as angles, horns, or spikes (widespread in Nearctic and Neotropical regions) . . . . . 19

19

return to couplet #18

  • In full-face view, head of major almost always possesses parallel or nearly parallel and straight or weakly convex sides; major extensively sculptured, usually with some and often a great deal of rugoreticulum on head (and, in a few species, on the body also); both major and minor almost always densely pilose, with hairs abundant on occiput in full-face view (southern U. S. to Argentina) (in case of difficulty, the closely similar Pheidole biconstricta group and Pheidole diligens group should also be scanned) . . . . . Pheidole fallax group
  • In full-face view, head of major with moderately convex sides, which with rest of head and mandibles form a roughly heart-shaped outline; most of body of major usually smooth and shiny; rugoreticulum present in a minority of species, and then only on the head, and further usually limited to the space between the eye and antennal fossa; most species sparsely to moderately pilose . . . . . 20

20

return to couplet #19

  • Possessing all of the following traits. Large species (Head Width of major l.4-l.9 mm); in major, all of posterior half of dorsal head surface foveolate and opaque, and occipital border seen in full face devoid of pilosity; at least a small patch of rugoreticulum present in major between eye and antennal fossa; head of minor narrowed posteriorly, with nuchal collar (Neotropical) (in case of difficulty, the closely related Pheidole diligens group and Pheidole fallax group should also be scanned) . . . . . Pheidole biconstricta group (in part - also #11)
  • Possessing one or more of the following traits. Head Width of major less than 1.4 mm or more than 1.9 mm in major, posterior half of dorsal head surface smooth and shiny, or carinulate; no rugoreticulum present in major between eye and antennal fossa; occiput of minor broad, lacking nuchal collar (Neotropical, one still undescribed species in southern Arizona) (in case of difficulty, the closely related Pheidole biconstricta group and Pheidole fallax group should also be scanned) . . . . . Pheidole diligens group