Key to Pheidole of the islands of the Southwest Indian Ocean

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This key to major and minor workers is based on: Fischer, G. and Fisher, B.L. 2013. A revision of Pheidole Westwood (Hymenoptera: Formicidae) in the islands of the Southwest Indian Ocean and designation of a neotype for the invasive Pheidole megacephala. Zootaxa 3683:301–356.

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Pheidole

FIGURE 1 Illustrations of measurements: Pheidole vulcan, full-face view (A), profile (B), and dorsal view (C) of major worker; Pheidole pulchella, oblique frontodorsal / dorsocaudal view (D) of minor worker. CI cephalic index: HW / HL * 100; SI scape index: SL / HW * 100; MDI mandible index: MDL / HW * 100; EI eye index: EL / HW * 100; FI metafemur index: MFL / HW * 100; PSLI propodeal spine index: PSL / HW * 100; LPpI lateral postpetiole index: PPL / PPH * 100; DPpI dorsal postpetiole index: PPW / PPL * 100; PpWI postpetiole width index: PPW / PTW * 100; PpLI postpetiole length index: PPL / PTL *100; PpHI postpetiole height index: PPH / PTH * 100

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  • Minors & majors: Relatively large species (WL minors 0.76–1.07, WL majors 1.06–1.65), with scapes and legs moderately long to very long (SI minors 120–209, FI minors 134–226, FL majors 1.01–168) and promesonotal process well-developed, angulate to subangulate, with a relatively deep angular groove in lateral view (Fig. 2A,B) . . . . . 2
  • Minors & majors: Mostly smaller species (WL minors 0.51–0.84, WL majors 0.70–1.22), with scapes and legs usually shorter (SI minors 85–130, FI minors 91–135, FL majors 0.55–1.06) and promesonotal process absent (Fig. 2C), or if present in major workers then the transverse groove in profile view at most shallowly concave (Fig. 2D) . . . . . 5
FIGURE 2 Pheidole indica, profile of minor (A) and major worker (B); Pheidole decepticon, profile of minor worker (C); Pheidole vulcan, profile of major worker (D).

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  • Minors: Postpetiole with convex ventral process (Fig. 3A). Majors: Head significantly longer than wide (CI 82–88). Posterior half of face lacking longitudinal rugae (Fig. 3B). Submedian hypostomal teeth moderately large. Postpetiole with small acute ventral process. Comoros Is., Mozambique . . . . . Pheidole komori
  • Minors: Postpetiole without ventral process (Fig. 3C). Majors: Head about as wide as long (CI 93–101). Face with longitudinal to posteriorly oblique rugae reaching toward posterolateral corners (Fig. 3D). Submedian hypostomal teeth small or inconspicuous. Postpetiole without ventral process . . . . . 3
FIGURE 3 Pheidole komori, profile of minor (A) and full-face view of major worker (B); Pheidole indica, profile of minor worker (C); Pheidole ragnax, full-face view of major worker (D).

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  • Minors: Head almost 50% longer than wide (CI 67–72) with raised occipital carina (Fig. 4A), metafemur very long, more than twice as long as head width (FI 209–226). Majors: Frontal carinae and antennal scrobe absent or inconspicuous (Fig. 4B), legs comparatively long (FI 99). Mayotte . . . . . Pheidole ragnax
  • Minors: Head relatively shorter (CI 72–88) and without raised occipital carina (Fig. 4C), metafemur shorter (FI 134–170). Majors: Frontal carinae and antennal scrobe present and conspicuous (Fig. 4D), legs shorter (FI 73–91) . . . . . 4
FIGURE 4 Pheidole ragnax, full-face views of minor (A) and major worker (B); Pheidole indica, full-face view of minor worker (C); Pheidole fervens, full-face view of major worker (D).

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  • Minors: Scape and metatibia pilosity mostly subdecumbent to suberect (Fig. 5A), metanotal groove in profile well-impressed (Fig. 5B), eyes moderately large (mean EI 22), and propodeal spines relatively short (mean PSLI: 12). Majors: Frontal carinae reaching at least 4/5 of the distance to posterior head margin, scrobe area and sides of head punctate to weakly punctate, in full-face view with coarse suberect hairs laterally (Fig. 5C). (Mauritius) widespread, introduced species . . . . . Pheidole fervens
  • Minors: Scape and metatibia pilosity decumbent to subdecumbent, plus longer suberect hairs along outer edge (Fig. 5D), metanotal groove not or barely impressed in profile (Fig. 5E), eyes slightly larger (mean EI 28), and spines relatively longer (mean PSLI: 16). Majors: Frontal carinae reaching 3/4 of the distance to posterior head margin, scrobe area and sides of head superficially punctate, in full-face view with decumbent to subdecumbent hairs laterally (Fig. 5F). (Comoros Is., Madagascar, Mauritius, Mayotte, Seychelles) widespread, introduced species . . . . . Pheidole indica
FIGURE 5 Pheidole fervens, dorsal view of scape (A) and profile (B) of minor, and full-face view of major worker (C); Pheidole indica, dorsal view of scape (D) and profile (E) of minor worker and full-face view of major worker (F).

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  • Minors & majors: Postpetiole in profile with large to moderately large, usually convex, ventral process (Fig. 6A), in some major workers widely subtriangular, but never acute (Fig. 6B), and postpetiole almost always higher than petiole (PpHI minors 100–146, PpHI majors 104–123). Minors: Face entirely smooth and shiny and scapes moderately short (SI 107–130), head shape oval, posterior head margin in full-face view rounded to medially straight (Fig. 6C), promesonotum in profile roundly convex: Majors: Submedian hypostomal teeth always small to inconspicuous and median process absent . . . . . 6
  • Minors & majors: Postpetiolar ventral process absent (Fig. 6D), or if present in major workers, then small and acute (Fig. 6E), never convex or broadly triangular in profile, and postpetiole usually lower than petiole, only very rarely higher in major workers (PpHI minors 73–97, PpHI majors 79–106). Minors: Face usually punctate, if face entirely smooth and shiny then head shape posteriorly more broadly transverse and scapes shorter (SI 91–98) (Fig. 6F), promesonotum in profile flatly convex and elongate. Majors: Submedian hypostomal teeth never small to inconspicuous, but relatively large, median process present or absent . . . . . 8
FIGURE 6 Pheidole megacephala, full-face view (A) and profile (B) of minor and full-face view of major worker (C); Pheidole braueri, full-face view of minor worker (D); Pheidole dodo, profile of minor worker (E); Pheidole vulcan, full-face view (F) and profile (G) of major worker.

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  • Minors: Standing hairs relatively fine and acute, abundant, and with several shorter hairs between longer pilosity (Fig. 7A). Majors: Postpetiolar ventral process slightly angulate to subtriangular in profile and small to moderately large, not convex, standing hairs relatively fine and acute (Fig. 7B). Comoros Is., Juan de Nova Is., Mayotte, Seychelles . . . . . Pheidole decepticon
  • Minors: Standing hairs relatively thicker, often blunt or bifurcate apically, and usually less abundant, with few or almost no shorter hairs between longer pilosity (Fig. 7C). Majors: Postpetiolar ventral process larger and convex, standing hairs thicker (Fig. 7D), often blunt or apically bifurcate . . . . . 7
FIGURE 7 Pheidole decepticon, profile of minor (A) and major worker (B); Pheidole megacephala, profile of minor (C) and major worker (D).

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  • Minors: Head about 0.9 times as wide as long (CI 86–92) and postpetiole about 0.8 times the length of petiole (PpLI 70–91) (Fig. 8A). Majors: Head usually heart shaped with posterior emargination moderately deep, sides of head strongly convex, posterior 1/3 to 1/4 of face, behind level where scapes end, smooth and shiny except for weak median rugae (Fig. 8B), posterolateral corners of head in profile ventrally smooth and shiny, at most with microsculpture present (Fig. 8C). (Comoros, Juan de Nova Is., Madagascar, Mauritius, Mayotte, Réunion, Seychelles) globally introduced species . . . . . Pheidole megacephala
  • Minors: Head slightly narrower (CI 82–87) and postpetiole shorter, about 0.7 times the length of petiole (PpLI 63–71) (Fig. 8D). Majors: Head less heart shaped, with posterior emargination relatively shallow (Fig. 8E), posterior 1/3 to 1/4 of head not completely smooth and shiny, some specimens superficially punctate, and some specimens with few to several, short, irregular, longitudinal rugulae, posterolateral corners of head in profile ventrally with punctate to weakly punctate sculpture (Fig. 8F). Comoros Is . . . . . Pheidole megatron
FIGURE 8 Pheidole megacephala, profile of minor (A), full-face view (B) and profile (C) of major worker; Pheidole megatron, profile of minor (D), full-face view (E) and profile (F) of major worker.

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  • Minors: Face smooth (Fig. 9A) to medially superficially punctate and laterally punctate to weakly punctate, with scape pilosity mostly suberect (Fig. 9B), and eyes relatively large (EI 22–24, mean 24). Majors: Frontal carinae strongly developed and laterally extended, obscuring part of antennal scrobe (Fig. 9C). Seychelles . . . . . Pheidole braueri
  • Minors: Either face mostly punctate to strongly punctate, sometimes overlain with faint rugulae (Fig. 9D), or face sculpture more reduced, then scape pilosity decumbent to subdecumbent (Fig. 9E) and eyes slightly smaller (P. dodo: EI 18–22, mean 21). Majors: Frontal carinae absent or short and inconspicuous, never laterally extended and obscuring part of antennal scrobe (Fig. 9F) . . . . . 9
FIGURE 9 Pheidole braueri, full-face view of syntype minor (A), non-type minor (B), and of major worker (C); Pheidole parva, full-face view of minor worker (D); Pheidole dodo, full-face view of minor worker (E); Pheidole vulcan, full-face view of major worker (F).

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  • Minors: Postpetiole usually about as long as high (LPpI 91–115, mean 102) and pronotum laterally mostly smooth and shiny (Fig. 10A). Majors: Posterior portion of face and of posterolateral lobes smooth and shiny, without rugae or punctures (Fig. 10B). Mauritius . . . . . Pheidole dodo
  • Minors: Either postpetiole longer than high (LPpI 114–163) (Fig. 10C) or pronotum laterally not mostly smooth and shiny (Fig. 10D). Majors: Face and posterolateral lobes never partly smooth and shiny, but rugoreticulate and punctate to superficially punctate (Fig. 10E) . . . . . 10
FIGURE 10 Pheidole dodo, profile of minor (A) and full-face view of major worker (B); Pheidole vulcan, profile of minor worker (C); Pheidole parva, profile of minor worker (D); Pheidole vulcan, full-face view of major worker (E).

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  • Minors: Postpetiole distinctly higher than long (LPpI 83–95) (Fig. 11A) and on average 1.4 times wider than long (DpPI 125–150) (Fig. 11B). Majors: Head distinctly longer than wide (CI 88–93) (Fig. 11C). (Mauritius, Seychelles, Saudi Arabia, United Arab Emirates) widespread, probably introduced species . . . . . Pheidole parva
  • Minors: Postpetiole at least as long as high or longer (LPpI 114–163) (Fig. 11D) and on average about as wide as long (DpPI 86–109) (Fig. 11E). Majors: Head about as long as wide (CI 95–102) (Fig. 11F) . . . . . 11
FIGURE 11 Pheidole parva, profile (A) and dorsal view (B) of minor and full-face view of major worker (C); Pheidole vulcan, profile (D) and dorsal view (E) of minor and full-face view of major worker (F).

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  • Minors (major unknown): Head posteriorly superficially punctate to smooth, mesosoma sculpture reduced, mostly very faintly punctate (Fig. 12B), sometimes overlain with superficial rugulae, scapes longer, on average 1.2 times longer than width of head (SI 117–122) and postpetiole significantly longer than wide (DPpI 86) (Fig. 12B). Mayotte . . . . . Pheidole loki
  • Minors: Head and majority of mesosoma both uniformly punctate to weakly punctate, promesonotum sometimes overlain with transverse rugulae (Fig. 12A), scapes on average 1.0 to 1.1 times longer than width of head (SI 96–122), and postpetiole on average as long as wide (DPpI 88–109) (Fig. 12A). Majors: Promesonotum dorsally with transverse rugulae, posterior process in profile weakly defined with inconspicuous to shallowly concave transverse groove, postpetiole in dorsal view with large lateral . . . . . 12
FIGURE 12 Pheidole vulcan, dorsal view of minor worker (A); Pheidole loki, dorsal view of minor worker (B).

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  • Minors: Mandibles and scapes relatively short (MDI 54–63, SI 96–106), postpetiole about 1.2 times longer than high (LPpI 114–120), standing hairs on mesosoma abundant (Fig. 13A). Majors: Promesonotal process high in profile view, with weakly impressed transverse groove, propodeal spines relatively long and spinose (PSLI 14–17), postpetiole higher than long (LPpI 83–95), and standing hairs on mesosoma abundant, relatively flexuous (Fig. 13B). Comoros Is . . . . . Pheidole vulcan
  • Minors: Mandibles and scapes slightly longer (MDI 60–73, SI 102–122), postpetiole about 1.4 times longer than high (LPpI 122–163), standing hairs on mesosoma comparatively scarce (Fig. 13C). Majors: Promesonotal process lower, with a more concavely impressed groove, propodeal spines shorter and subtriangular (PSLI 10–14), postpetiole usually longer than high (LPpI 90–126), and standing hairs less abundant and less flexuous (Fig. 13D). Comoros Is., Mayotte . . . . . Pheidole jonas
FIGURE 13 Pheidole vulcan, profile of minor (A) and major worker (B); Pheidole jonas, profile of minor (C) and major worker (D).