Key to the worker caste of extant Prenolepis species

1 In profile view, petiole narrow and elongate (PetWI <55) with a rounded dorsal apex of the scale (Figs 51, 52, 54–56); in fullface view, torulae not touching the posterior border of clypeus (Figs 39–41, 43, 44, 50)..............................2

- In profile view, petiole short and broad (PetWI> 55) and forward-inclined with a sharply-angled dorsal apex of the scale (Fig 53); in full-face view, torulae overlapping with the posterior border of clypeus (Figs 38, 42, 45–49)................... 7

2 Ocelli absent; compound eyes surpassing the lateral margins of head in full-face view; scapes with appressed setae.......3

- Three small ocelli present; compound eyes not surpassing the lateral margins of head in full-face view; scapes with erect setae....................................................................................................5

3 Small (TL <2.70mm), robust with short legs (HTI <150), antennae (SI <160), and mesosoma (BLI <175); body light to medium brown; in profile view, posterodorsal part of propodeum obtusely angled (Fig 20); petiolar scale low in profile with a weakly sinuate anteroventral outline (Fig 54)....................................................... P. jacobsoni

- Medium to large (TL> 2.70mm), gracile with elongate legs (HTI> 185), antennae (SI> 175), and mesosoma (BLI> 175); body uniformly dark brown to black; posterodorsal part of propodeum in profile view roundly produced, much higher than pronotum (Figs 21, 27); petiolar scale high in profile with a roughly subtriangular anterodorsal outline and almost straight ventral outline (Figs 55, 56)............................................................................... 4

4 Overall cuticle shiny and smooth to lightly reticulate; pubescence completely absent on the dorsal surface of pronotum, propodeum, or gaster................................................................................ P. jerdoni

- Overall cuticle dull and finely reticulate; thick patches of pubescence present on the dorsal surface of pronotum, propodeum, and gaster.................................................................................. P. subopaca

5 Body uniformly dark brown to black; head roughly subtriangular in shape; cuticle of head lightly reticulate; ectal surface of mandibles with light longitudinal striations; in profile view, the ventral surface of petiole almost straight (Fig 55).. P. fisheri

- Head and mesosoma light brown in overall color; ectal surface of mandibles smooth and shiny; in profile view, the ventral surface of petiole is curved upward toward the anterior articulation with the metanotum (Figs 51, 52).................... 6

6 Body light brown with little to no difference in color among head, mesosoma, and gaster; head roughly square in full-face view; cuticle of head lightly reticulate; in profile view, dorsal outline of petiolar scale roughly subtriangular in shape (Fig 51)............................................................................................. P. darlena

- Head and mesosoma light brown and gaster distinctly dark brown to black; head roughly subtriangular in full-face view; cuticle of head finely rugoreticulate; in profile view, petiole club-shaped with dorsal outline of petiolar scale rounded (Fig 52).............................................................................................. P. fustinoda

7 In full-face view, compound eyes strongly convex, surpassing the lateral margins of head; anterior border of clypeus without a pair of prominent anterolateral lobes............................................................... P. naoroji

- In full-face view, compound eyes weakly convex and not surpassing the lateral margins of head; anterior border of clypeus with a pair of prominent anterolateral lobes (Figs 38, 42, 45, 46, 48, 49)......................................... 8

8 Large (TL> 4.25mm); in profile view, propodeum with a rounded dorsal face (Fig 23); head and mesosoma yellow-brown, and gaster dark brown to black................................................................. P. melanogaster

- Small to medium (TL <4.25mm); in profile view, propodeum with a flat to softly rounded dorsal face, posterodorsally obtusely angled (Figs 15, 19, 22, 25, 26).................................................................. 9

9 Scapes with erect setae; body dark brown, with a faint blue cuticular iridescence.......................... P. angularis

- Scapes with appressed setae; body light to dark brown, without a faint blue cuticular iridescence..................... 10

10 Compound eyes round in shape, medium-sized (distinctly smaller than those of other Prenolepis species); interocular distance relatively long (REL3 <35)..................................................................... P. mediops

- Compound eyes oval in shape, relatively large; interocular distance relatively short (REL3> 40)..................... 11

11 Ectal surface of mandibles smooth and shiny, without longitudinal striations; in profile view, border of mesonotum bulges and rises above pronotum (Fig 26)................................................................. P. shanialena

- Ectal surface of mandibles with deep longitudinal striations.................................................. 12

12 In profile view, mesosoma more robust at the mesonotal constriction (Fig 25); distributed across southeastern Europe, the Balkan Peninsula, Turkey, and east to Georgia ............................................................ P. nitens

- In profile view, mesosoma slender at the mesonotal constriction (Fig 19); distributed across North America, from southern Canada to Mexico ............................................................................. P. imparis