Key to Malagasy Erromyrma, Monomorium, Syllophopsis and Trichomyrmex species

This worker key is based on:

After the publication of this key Monomorium species have been reorganized into the genera: Monomorium, Syllophopsis and Trichomyrmex. This key reflects this new nomenclature.

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 * Monomorium
 * Syllophopsis
 * Trichomyrmex

1

 * Antenna 11-segmented (M. monomorium species group) . . . . . 2


 * Antenna 12-segmented (various species groups) . . . . . 3

2
return to couplet #1
 * Metanotal groove weakly impressed; in profile, propodeum rather elongate and petiolar node always conical, its dorsum tapered (depigmented yellow to brown) . . . . . Monomorium exiguum


 * Metanotal groove strongly impressed; in profile, propodeum evenly rounded and petiolar node may be thick, broadly rounded (dark reddish-brown to black) . . . . . Monomorium nigricans

3
return to couplet #1
 * Palps long (PF 5,3); propodeum usually lacking standing setae, where present these short and fine; occipital carina strongly defined and conspicuous along rear margin of head when head viewed in profile; mandible armed with five distinct teeth (M. shuckardi species group) . . . . . 4


 * Palps shorter (PF 3,3 or less); propodeum usually with standing setae, but if these lacking, then mandible armed with four teeth, or with three distinct teeth and a small to minute denticle or angle; occipital carina vestigial or short, not conspicuous along rear margin of head when head viewed in profile . . . . . 7

4
return to couplet #3
 * Head and mesosoma finely striolate; in profile, propodeum without a distinct angle between its dorsal and declivitous faces . . . . . Royidris robertsoni


 * Head and mesosoma finely striolate-microreticulate, microreticulate-punctate with or without unsculptured areas, or head and dorsum of mesosoma smooth and shining; propodeum in profile with blunt to sharply defined propodeal angle . . . . . 5

5
return to couplet #4
 * Antennal scape very long, extending beyond vertex of head capsule (SI 113–132) larger (HW 0.62–0.72 mm), depigmented yellow ants . . . . . Royidris notorthotenes


 * Antennal scape shorter, barely or not attaining vertex (SI 90–108); if yellowish, then much smaller (HW 0.35–0.47 mm compared with 0.62–0.72 mm) . . . . . 6

6
return to couplet #5
 * In full-face view, frons of head capsule densely microreticulate-punctate; generally larger species (HW 0.46–0.72 mm, usually 0.55 mm<) . . . . . Royidris shuckardi


 * In full-face view, frons of head capsule finely striolate-microreticulate or smooth and shining; generally smaller species (HW 0.35–0.47 mm compared with 0.46–0.72 mm, usually 0.55 mm ≥) . . . . . Royidris clarinodis

7
return to couplet #3
 * Mandible distinctly longitudinally striate, maximum number of teeth four . . . . . 8


 * Mandible smooth and shining, except for piliferous pits, with three to five teeth . . . . . 12

8
return to couplet #7
 * In full-face view, frons of head capsule smooth, with exception of piliferous punctures, fine rugulae on vertex (M. destructor) and fine, circular striolae around antennal insertions (M. destructor species group) . . . . . 9


 * In full-face view, frons of head capsule sculptured, sculpture varying from superficial reticulation to shagreenate-punctate (M. salomonis species group) . . . . . 10

9
return to couplet #8
 * Head and mesosoma brown to dark brown . . . . . Trichomyrmex robustior


 * Head and mesosoma yellow to light brownish-yellow . . . . . Trichomyrmex destructor

10
return to couplet #8
 * Mesosoma possessing one or more pairs of erect and/or sub-erect setae . . . . . Monomorium pharaonis


 * Mesosoma without standing setae . . . . . 11

11
return to couplet #10
 * In full-face view, frons of head capsule shining, with surface sculpture confined to faint reticulation, the vertex more noticeably shagreenate; scape shorter (SI < 100) . . . . . Monomorium willowmorense


 * In full-face view, frons of head capsule opaque, reticulate to shagreenate-punctate; scape longer (SI 100 >) . . . . . Monomorium subopacum

12
return to couplet #7
 * Either frontal lobes separated by a strip of posterior sector of clypeus that is clearly wider than either of them, or, if frontal lobes closely approximated, metanotal groove strongly indented and propodeum smooth; propodeal dorsum rounding into declivitous face without distinct angle; propodeal denticles always absent; fine, transverse ridges always absent from underside of petiolar peduncle and node; anteroventral postpetiolar process commonly vestigial or absent, rarely an inconspicuous lip and prominent only in M. latinode . . . . . 13


 * Frontal lobes usually closely approximated, and separated by a strip of posterior sector of clypeus that is narrower than either of them, or, if frontal lobes well separated, and metanotal groove deeply impressed, then propodeal dorsum meeting declivitous face at a distinct angle; propodeum often armed with flanges or denticles; several to many fine, transverse ridges present on underside of petiolar peduncle and node; anteroventral postpetiolar process usually distinct as sharp angle, conspicuous lip or spur (M. hanneli and M. hildebrandti species groups.) . . . . . 26

13
return to couplet #12
 * Mandible armed with five teeth; PF 3,3; propodeum elongate, its dorsum and sides finely and densely striolate (M. latinode species group) . . . . . Monomorium latinode


 * Mandible armed with three or four teeth (five teeth very rarely present in M. chnodes); PF 2,2 or 1,2; propodeum not as above, usually smooth on dorsum and sides (M. monomorium species group) . . . . . 14

14
return to couplet #13
 * In full-face view, clypeus strongly bidentate, each clypeal carina terminating in a sharp angle or denticle, the anteromedian clypeal margin between the clypeal projections often straight; eyes large, eye length between 1/4th and 1/5th length of side of head capsule (body of ant concolorous yellow or brown, gaster may be slightly darker shade than mesosoma) . . . . . 15


 * In full-face view, clypeus usually weakly emarginate to weakly convex, if clypeus tending to bidentate then anteromedian margin of clypeus usually indented between anteromedian clypeal projections, body of ant is distinctly bicolored or eye is smaller, eye length 1/5th < length of side of head capsule . . . . . 16

15
return to couplet #14
 * Propodeal spiracle very large, ≈ same width as antennal segments a3–9; petiolar node higher, tending to cuneate . . . . . Monomorium madecassum


 * Propodeal spiracle minute, pinhole-like, width << antennal segments a3–9; petiolar node lower, conical . . . . . Monomorium denticulum

16
return to couplet #14
 * Mandible always clearly armed with three teeth with no trace of a smaller, basal tooth or denticle . . . . . 17


 * Mandible characteristically armed with four teeth, albeit basal tooth may be reduced to a minute, offset denticle or angle (rarely absent in individuals of M. flavimembra, whose workers have a bright reddish- or yellowish-brown body and yellowish appendages), rarely with five teeth (some M. chnodes) . . . . . 18

17
return to couplet #16
 * In profile clypeus sloping towards mandibles at acute angle; in full-face view clypeus projecting forward so that its anterior margin adjoins or partially obscures basal margin of mandibles; metanotal groove deeply impressed but almost always without broad cross-ribs; variously colored from orange to dark reddish-black or bicolored, but where head is light colored, antennal scape is conspicuously darker than head capsule . . . . . Monomorium versicolor


 * In profile, clypeus almost at right angle to mandibles; in full-face view, anterior margin of clypeus largely straight, clypeus not projecting forward, leaving a gap between clypeus and mandibles; metanotal groove deeply impressed, broad cross-ribs always present; concolorous orange, with antennal scape of same color as head capsule . . . . . . Monomorium platynode

18
return to couplet #16
 * Head and gaster uniformly dark brown to black, contrasting with yellowish or bicolored yellow-and-brown mesosoma; petiolar node low, broadly conical to tumular, scarcely higher than postpetiole . . . . . Monomorium floricola


 * Either concolorous, or head and gaster not both uniformly dark in color with a lighter colored mesosoma; petiolar node variable but usually distinctly higher than postpetiole . . . . . 19

19
return to couplet #18
 * In profile, mesosoma straight and at higher level than propodeum; propodeal spiracle very large, ≈ diameter of antennal segments a3–a9; five teeth occasionally present, all non-apical mandibular teeth usually of same size; propodeum short, about as long as high; antennal scape relatively short (SI 67–76) (densely hairy, bright yellow ants) . . . . . Monomorium chnodes


 * In profile, mesosoma, if straight, on same level as propodeum; propodeal spiracle generally smaller, commonly pinhole-like; maximum of four teeth, basal tooth frequently distinctly smaller than other non-apical teeth and reduced to minute denticle or angle in several taxa; propodeum usually longer than high; antennal SI usually 80> . . . . . 20

20
return to couplet #19
 * In full-face view, antennal scapes very long, scapes normally reaching or even slightly exceeding vertex of head capsule (SI 100 >), in rare, very small individuals with scape index slightly less than 100, head darker than mesosoma; profile of combined mesosoma and propodeum straight (except for indentation of metanotal groove), propodeum elongate with indistinct angle between propodeal dorsum and its declivitous face; mesosoma often with 8> pairs of setae; mesopleuron usually with distinct sculpture, often reticulate-punctate (reddish-brown ants which normally have darker head and gaster) . . . . . Monomorium sakalavum


 * In full-face view, antennal scapes usually shorter, if exceeding vertex, and profile of combined mesosoma and propodeum straight, then mesopleuron smooth, or head of same color intensity as mesosoma and mesosoma with only three prominent pairs of standing setae, or propodeum rounded in a convex curve towards its declivitous face . . . . . 21