Pheidole caldwelli

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Pheidole caldwelli
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Attini
Genus: Pheidole
Species group: knowlesi
Species: P. caldwelli
Binomial name
Pheidole caldwelli
Mann, 1921

MCZ-ENT00008697 Pheidole caldwelli hal.jpg

MCZ-ENT00008697 Pheidole caldwelli had.jpg

Specimen Label

Fisher et al. (2016) - Mann (1921) wrote that it was “very common in, and apparently restricted in distribution to, the mountains about Nadarivatu (Viti Levu), where numerous colonies were found beneath stones and logs”. R.W. Taylor collected a series of workers (stored at ANIC) from a rotten log in rainforest also in Nadarivatu district in 1962. In the recent ant survey this species was also collected from localities in the upland forests of southeastern Viti Levu and a lone worker was found on Moala Island. These collections were all made from sifted leaf-litter in primary rainforest and in elevations between 300 and 800m.


Fisher et al. (2016) - knowlesi group: Major worker: large (HW 1.55–1.62mm); head, mesosoma, postpetiole, most of petiole and anterior half of first gastral tergite entirely sculptured with punctures; frons with irregular, longitudinal rugulae and with median ocellus present, posterolateral lobes rugoreticulate; antennal scrobes relatively narrow; anterior clypeal margin straight with median notch present; hypostoma bearing stout submedian teeth, median tooth absent or inconspicuous. Minor worker: head, mesosoma, petiole, postpetiole entirely punctate, often punctures very coarsely and overlain with irregular rugulae. Scapes, dorsum of coxae, legs and anterior 1/3 to 1/4 of first gastral tergite punctate. Promesonotum in profile with short process present on posterior declivity; propodeal spines longer than distance between their relatively massive bases and tapering apically. Postpetiole large and much more voluminous than petiole node in profile. Queen: large (WL 1.66), with relatively short legs (FI 75); anterior clypeal margin transverse with median notch; scutum entirely covered with subparallel longitudinal rugulae, anterior half of first gastral tergite strongly longitudinally rugulose and punctate.

This species is rather distinct within the knowlesi group and easily distinguishable from the other five species by its larger size and the extent of punctate and rugose sculpture, which covers almost every surface of the body, including the anterior part of the gaster. The major and minor workers are also characterized by distinctly longer propodeal spines that are at least as long as, to distinctly longer than the distance between their bases and the presence of a process at the promesonotal posterior declivity. Major workers and queens also differ from the other species in the group in having large, stout submedian hypostomal teeth and an absent median tooth. The minors can also be recognized by the relatively large and voluminous postpetiole. Pheidole caldwelli has morphological affinities to both the knowlesi and roosevelti groups, but preliminary next-generation sequencing analysis (unpublished data) places it as part of the monophyletic knowlesi group, and thus we include it therein. Shared characters between P. caldwelli and species from the roosevelti group are longer spines, presence of a promesonotal process and its larger size. A unique character state for P. caldwelli that sets it apart from all other species of the two groups is the complete absence of the median hypostomal tooth in major workers and queens.

Keys including this Species


Distribution based on Regional Taxon Lists

Indo-Australian Region: Fiji (type locality).

Distribution based on AntMaps


Distribution based on AntWeb specimens

Check data from AntWeb




The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

  • caldwelli. Pheidole caldwelli Mann, 1921: 434, fig. 14 (s.w.q.) FIJI IS.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.



Fisher et al. (2016) – Major (n = 5): HW1.55–1.62 (1.59), HL 1.62–1.66 (1.64), SL 0.79–0.82 (0.81), MDL 0.79–0.81 (0.80), EL 0.18–0.20 (0.19), WL 1.12–1.24 (1.19), PNW 0.69–0.71 (0.70), PTL 0.46–0.49 (0.47), PPL 0.28–0.29 (0.29), PTH 0.29–0.31 (0.30), PPH 0.31–0.35 (0.32), PTW 0.25–0.27 (0.26), PPW 0.46–0.53 (0.50), PSL 0.36–0.38 (0.37), MFL 1.0–1.03 (1.01), MTL 0.73–0.78 (0.75), CI 95–98 (97), SI 50–52 (51), MDI 50–51 (50), EI 12–13 (12), FI 62–66 (64), PpI 67–75 (71), LPpI 83–90 (88), DPpI 164–183 (175), PpWI 170–200 (190), PpHI 103–113 (108). Ground sculpture punctate on head, mesosoma, petiole, postpetiole and anterior half of first gastral tergite and sides of first gastral sternite. Mandibles, median area of clypeus, anterodorsal face of petiole and remainder of gaster smooth and shiny. Head shape in full-face view subrectangulate (CI 95–98) with weakly convex sides. Anterior margin of clypeus transverse, medially notched. In profile, head between frons and posterodorsal lobes with shallow impression. Frontal carinae well-defined anteriorly and medially, extending above antennal scrobe and ending at about 2/3 towards posterior head margin. Frons with ill-defined, irregular rugulae and bearing a single median ocellus in all examined specimens. Irregular, partly reticulate rugulae also present lateral of relatively narrow antennal scrobe, replaced by reticulum posterior of scrobe area and frons. Scape length equals ½ of head width (SI 50–52), when in repose, reaching end of frontal carinae, with sparse, short, and mostly decumbent pilosity and few longer erect hairs along outer edge. Hypostoma without visible median tooth, submedian teeth well-developed and stout. Promesonotum in profile convex with small, rounded posterior process present, metanotal groove not impressed, propodeum compact and short, significantly higher than long in profile, with very short dorsal face and oblique posterior declivity. Spines long, acute and thick at base. In dorsal view, pronotal humeri with very short, but sharply angulate and projecting. Punctuate sculpture on mesosoma mostly covered by weak, irregular rugoreticulum. Coxae often with patches of weak to superficial sculpture. Metatibia pilosity same as scape pilosity. Standing hairs short, suberect, not abundant, of yellow golden colour, shorter, decumbent pilosity present as well. Colour reddish to dark brown, antennae and legs yellowish light brown.

Minor (n = 5): HW 0.55–0.67 (0.63), HL 0.62–0.75 (0.70), SL 0.63–0.75 (0.71), MDL 0.42–0.46 (0.44), EL 0.12–0.15 (0.13), WL 0.80–0.93 (0.88), PNW 0.38–0.45 (0.43), PTL 0.28–0.34 (0.31), PPL 0.18–0.21 (0.20), PTH 0.16–0.18 (0.17), PPH 0.17–0.19 (0.18), PTW 0.13–0.17 (0.15), PPW 0.20–0.25 (0.24), PSL 0.15–0.25 (0.22), MFL 0.72–0.84 (0.79), MTL 0.56–0.63 (0.60), CI 89–92 (90), SI 110–115 (113), MDI 66–80 (71), EI 21–22 (21), FI 124–131 (127), PpI 53–57 (55), LPpI 105–117 (110), DPpI 111–123 (118), PpWI 148–172 (161), PpHI 109–113 (110). Ground sculpture punctate on head including scapes, mesosoma, petiole, postpetiole, dorsum of coxae, legs and anterior third of first gastral tergite. Punctures on head and mesosoma often coarse and overlain by weak, irregular reticulum. Mandibles and remainder of coxae and gaster smooth and shiny. Head shape oval with convex sides, posterior margin moderately wide with rounded corners and medially very shallowly concave. Eyes relatively small, with 6–7 ommatidia in the longest row. Scapes, when in repose, surpassing posterior head margin by about one eye length, scape pilosity very short and erect to suberect. Promesonotal outline in profile convex, broken by a short to distinct process present on posterior declivity, sometimes followed by a second, much smaller process before very shallowly impressed metanotal groove. Propodeum about as high as long, spines often very long, stout and apically acute, at least as long as distance between their bases—up to about twice as long. Metatibia pilosity similar to scape pilosity. Postpetiole large and much more voluminous than petiole, higher than petiole (PpHI 109–113), slightly longer than high (LPpI 105–117), and in dorsal view about 1.2 times wider than long (DPpI 111–123). Standing hairs on head and mesosoma almost absent, only few short erect hairs present on anterior head and posterior gaster. Other areas with shorter erect to suberect pilosity present. Head and body reddish to dark brown, mandibles, funiculus and legs slightly lighter coloured.


Fisher et al. (2016) - (n = 1): HW 1.33, HL 1.20, SL 0.75, MDL 0.71, EL 0.30, WL 1.66, PNW 1.1, PTL 0.6, PPL 0.35, PTH 0.44, PPH 0.47, PTW 0.39, PPW 0.68, PSL 0.39, MFL 1.0, MTL 0.74, CI 111, SI 56, MDI 53, EI 23, FI 75, PSLI 29, LPpI 74, DPpI 194, PpWI 174, PpHI 107. Head wider than long (CI 111), anterior margin of clypeus with median notch. Scapes relatively short (SI 56), with very short subdecumbent to suberect pilosity and with few longer, erect hairs along outer edge. Head punctate, frontal carinae long and reaching about 4/5 towards posterior head margin. Frons with long, uninterrupted longitudinal rugae, sides and area posterior of ocelli and narrow, but well-developed, scrobes rugoreticulate. Eyes relatively small (EI 23). Median hypostomal tooth reduced or inconspicuous, submedian teeth large and stout. Mesosoma coarsely rugulose-punctate without smooth patches. Scutum with many subparallel carinae covering the whole length and width of the sclerite. Propodeum laterally with longitudinal and oblique rugulae, spines relatively long (PSL 0.39), wide at bases and apex blunt. Petiole strongly convex ventrally, punctate and rugulose, only median area of anterodorsal face smooth. Postpetiole in profile about as high as petiole with convex ventral process, about 1.75 times as wide as petiole (PpWI 174) with laterally extended, angulate corners, its dorsum with transverse rugulae. Standing hairs moderately long and abundant, mostly suberect and yellowish light brown. Colour reddish brown, mandibles and smooth part of gaster darker, antennae and legs slightly lighter colored.

Type Material

Fisher et al. (2016) - FIJI, Viti Levu, Nadarivatu (W. M. Mann). Syntypes: 24 minor workers, 4 major workers (Museum of Comparative Zoology type no. 8697, examined); 11 minor workers, 10 major workers, 3 queens (National Museum of Natural History, examined).


References based on Global Ant Biodiversity Informatics

  • Dlussky G.M. 1994. Zoogeography of southwestern Oceania. Zhivotnoe naselenie ostrovov Iugo-Zapadnoi Okeanii ekologo-geograficheskie issledovanii 48-93.
  • Fischer G., E. M. Sarnat, and E. P. Economo. 2016. Revision and microtomography of the Pheidole knowlesi Group, an endemic ant radiation in Fiji (Hymenoptera, Formicidae, Myrmicinae). PLoS ONE 11(7): e0158544. doi:10.1371/journal.pone.0158544
  • Mann W. M. 1921. The ants of the Fiji Islands. Bull. Mus. Comp. Zool. 64: 401-499.
  • Sarnat Eli M. 2009. The Ants [Hymenoptera: Formicdiae] of Fiji: Systematics, Biogeography and Conservation of an Island Arc Fauna. 80-252
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  • Ward, Darren F. and James K. Wetterer. 2006. Checklist of the Ants of Fiji. Fiji Arthropods III 85: 23-47.
  • Wheeler W.M. 1935. Check list of the ants of Oceania. Occasional Papers of the Bernice Pauahi Bishop Museum 11(11):1-56.
  • Wheeler, William Morton.1935.Checklist of the Ants of Oceania.Occasional Papers 11(11): 3-56
  • Wilson E.O., and G.L. Hunt. 1967. Ant fauna of Futuna and Wallis islands, stepping stones to Polynesia. Pacific Insects 9(4): 563-584.
  • Wilson, Edward O. and George L. Hunt. 1967. Ant Fauna of Futuna and Wallis Islands, Stepping Stones To Polynesia. Pacific Insects. 9(4):563-584.
  • Wilson, Edward O. and Hunt, George L. Jr. 1967. Ant Fauna of Futuna and Wallis Islands, Stepping Stones to Polynesia. Pacific Insects. 9(4):563-584