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.
These tiny ants, distinguished by antennal segmentation reduced from 12 to 11, as well as by the possession of antennal scrobes and heavy cephalic sculpturing in the major caste, range from Panama to the Brazilian Amazon. They are evidently nowhere common. Their anatomy, especially that of the minor caste, suggests that they were derived from within the flavens group as currently recognized, with tachigaliae forming one line and the other four species a second, independent line. The members of the tachigaliae group superficially resemble those of the transversostriata group, which have 12-segmented antennae, but the similarity may be due to convergent evolution. One species, Pheidole bahai, described from a minor, was not seen during this study.
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- Major: dorsal surface of head covered by parallel longitudinal carinulae; pronotum lacks carinulae or rugoreticulum (Guianas) . . . . . Pheidole tachigaliae
- Major: dorsal surface of head covered by parallel transverse carinulae; pronotum with carinulae, rugoreticulum, or both . . . . . 2
return to couplet #1
- Major: head ventral to eye rugoreticulate (Colombia) . . . . . Pheidole dorsata
- Major: head ventral to eye carinulate . . . . . 3
return to couplet #2
- Major: mesonotal dorsum rugoreticulate. Minor: dorsal surface of head entirely foveolate and opaque (Costa Rica to Brazil and Peru) . . . . . Pheidole mendicula
- Major: mesonotal dorsum foveolate only, not rugoreticulate. Minor: dorsal surface of head either foveolate and opaque or else smooth and shiny . . . . . 4
return to couplet #3
- Major: anterior half of pronotal dorsum bears several irregular carinulae only. Minor: dorsal surface of head entirely foveolate and opaque; distance from genal margin to eye much less than the length of the eye (Amazonian Brazil and Peru) . . . . . Pheidole pedana
- Major: anterior half of pronotal dorsum rugoreticulate. Minor: dorsal surface of head entirely smooth and shiny; distance from genal margin to the eye greater than Eye Length (Suriname) . . . . . Pheidole gibbata