Key to Monomorium of the southwestern Australian Botanical Province

This worker key is based on: Heterick, B. E. 2009a. A guide to the ants of South-western Australia. Records of the Western Australian Museum, Supplement 76: 1-206. Part 2.

Monomorium kilianii has also been recorded from the south-west but the record of this eastern Australian species is very dubious. This ant is not included in this key.

This key includes the species Trichomyrmex destructor.

1

Compound eyes absent (may occasionally be represented by minute fleck of pigment) . . . . . Monomorium hildebrandti gp. sp. JDM 438

Compound eyes present, moderate to large in size . . . . . 2

2

return to couplet #1

Antenna 10-segmented . . . . . 3

Antenna 11 or 12-segmented . . . . . 4

3

return to couplet #2

PF 2,3; number of mandibular teeth 5; propodeum armed with sharp denticles . . . . . Monomorium decuria

PF 1,2; number of mandibular teeth 4; propodeum unarmed . . . . . Monomorium sydneyense

(pt.)

4

return to couplet #2

Antenna 11-segmented . . . . . 5

Antenna 12-segmented . . . . . 15

5

return to couplet #4

Viewed in profile, eye distinctly oblique, often reaching to venter of head capsule, distance from mandible usually much less than length of eye (Figure 600) . . . . . 6

Figure 600.

Viewed in profile, eye situated along longitudinal axis of head capsule, distance from mandible at most only slightly less than length of eye (Figure 601) . . . . . 7

Figure 601.

6

return to couplet #5

PF 2,2; head square (Figure 602) . . . . . Monomorium eremophilum

Figure 602.

PF 1,2; head rectangular (Figure 603) . . . . . Monomorium nanum

Figure 603.

7

return to couplet #5

Propodeum distinctly cuboidal, laterally carinate, or with lamellae on propodeal lobes extending to or near propodeum; propodeal and mesopleural sculpture often shagreenate-punctate (Figure 604) . . . . . 8

Figure 604.

Propodeum more-or-less rounded, with small, inconspicuous propodeal lobes; propodeal and mesopleural sculpture never shagreenate-punctate, usually absent, if present, then confined to a few striae, particularly around the lower mesopleuron (Figure 605) . . . . . 14

8

return to couplet #7

Mandible with three distinct teeth; eye small (approximately ≈ width of antennal scape); propodeum smooth and shining with only vestigial striae; propodeum with declivitous face long and oblique, carinate at sides and sometimes with small lamellae at propodeal angle (Figure 606); anterior clypeal margin rounded; long erect and suberect setae absent from mesosoma . . . . . Monomorium arenarium

Figure 606.

Mandible usually with four teeth and denticles (basal tooth may be minute or an offset angle); if clypeal margin rounded then eye larger; propodeum shagreenate or otherwise sculptured (e.g. Figure 607) . . . . . 9

Figure 607.

9

return to couplet #8

Yellow species or yellowish with reddish-brown head and gaster; erect and suberect setae on head and mesosoma; propodeum cuboidal to slightly elongate; eye large (eye width ≥ 2 × greatest width of antennal scape) (Figure 607). . . . . . Monomorium silaceum

Never with above combination of characters; if yellow with a cuboidal propodeum and large eye, then erect and suberect setae absent from head and mesosoma . . . . . 10

10

return to couplet #9

Mesonotal and mesopleural sectors of promesonotum distinctly microreticulate; in dorsal view, faint, longitudinal striae also often evident on mesonotal sector; eyes usually large (eye diameter > greatest antennal width) (Fig, 608); ant shades of reddish-orange to brown, alone or in combination . . . . . 11

Figure 608.

Mesonotal sector of promesonotum, at least, smooth and shining with microreticulate sculpture and faint, longitudinal striae always absent; if ant with strong microreticulation on mesopleural sector and on propodeum, then eyes usually moderate to small in non-yellow specimens (eye diameter ≤ greatest antennal width) (Figure 609: M. sydneyense Forel); colour various . . . . . 12

Figure 609.

11

return to couplet #10

In profile, mesosoma an even arc, metanotal grove appearing as a slit between promesonotum (which is short) and propodeum; metanotal groove with few if any cross ribs; eye generally oval, smaller (eye width 1–1.5 × greatest width of antennal scape); erect setae generally absent on mesosoma (Figure 610) . . . . . Monomorium aithoderum

Figure 610.

In profile, promesonotum evenly rounded anteriad, more-or-less straight posteriad, metanotal groove broad but shallow, often with distinct lateral cross-ribs; promesonotum elongate; eye commonly reniform, larger (eye width 2× greatest width of antennal scape); erect setae often present on mesosoma in SWBP specimens (Figure 611) . . . . . Monomorium stictonotum

Figure 611.

12

return to couplet #10

Eye moderate (eye width 1–1.5 × greatest width of antennal scape), oval (most workers) to slightly elongate (some bright yellow workers); viewed in profile, promesonotum flattened and truncated; colour very variable; erect and suberect setae absent from head, mesosoma and nodes in all bright yellow workers,usually also absent in non-yellow workers (see Figures 604, 609) . . . . . Monomorium sydneyense

Figure 604.

Figure 609.

(pt.)

Eye large, (eye width ≥ 1.5 × greatest width of antennal scape), mostly elongate; viewed in profile, promesonotum often more elongate and rounded; colour always yellow (head may be slightly darker); erect or suberect setae usually present at least on petiole and postpetiole . . . . . 13

13

return to couplet #12

Eye very large (eye width ≥ 2 × greatest width of antennal scape), mesopleural sector of promesonotum and propodeum with strong microreticulate sculpture; erect and suberect setae (if present) restricted to nodes (Figure 612) . . . . . Monomorium micula

Figure 612.

Eye smaller (eye width ≈ 1.5 × greatest width of antennal scape); mesopleural sector of promesonotum and propodeum lacking strong sculpture, cuticle relatively smooth and shining; erect and suberect setae often present on head and mesosoma (workers in many northern populations with conspicuous, erect humeral setae, but other raised setae lacking on promesonotum) (Figure 613) . . . . . Monomorium disetigerum

Figure 613.

14

return to couplet #7

Yellowish-brown to dark brown in all SWBP populations (if yellowish-brown, then head and gaster darker); propodeum relatively short and usually smoothly rounded (Figure 614); eye compact and ovate . . . . . Monomorium fieldi

Figure 614.

Uniformly yellow or yellow with first tergite of gaster also yellow, remaining tergites yellow-brown; propodeum usually relatively elongate (Figure 615); eye in larger specimens tending to large and elongate . . . . . Monomorium laeve

Figure 615.

15

return to couplet #4

Number of mandibular teeth and denticles three . . . . . Monomorium rothsteini

Number of mandibular teeth and denticles four to seven . . . . . 16

16

return to couplet #15

Eye much longer than wide, either distinctly elongate (Figure 616) coming to a point anteriad, or reniform (Figure 617); worker small (HW usually < 0.60 mm); brown or dark brown species . . . . . 17

Figure 616.

Figure 617.

Eye circular, subcircular, weakly elongate (not coming to a point anteriad), elliptical or ovoid (e.g. Figure 618); worker usually larger (HW mostly > 0.60 mm) . . . . . 18

Figure 618.

17

return to couplet #16

Eye elongate, reaching almost to mandible (Figure 616); mesosoma, propodeum and petiole strongly microreticulate; pilosity on promesonotum and propodeum consisting of dense, short setae; colour uniform dark brown . . . . . Monomorium anthracinum

Figure 616.

Eye reniform (Figure 617); microreticulation on body surface less marked, and confined to lower mesopleuron and propodeum, otherwise smooth and shining; pilosity consisting of sparse, erect and suberect setae; colour brown or tawny orange with dark brown gaster . . . . . Monomorium megalops

Figure 617.

18

return to couplet #16

Petiolar node long and low, barrel-shaped (Figure 619) . . . . . 19

Figure 619.

Petiolar node not as above (usually cuboidal, conical, cuneate or tumular) . . . . . 20

19

return to couplet #18

Head capsule trapezoidal in full-face view, narrowest at vertex (Figure 620); frons longitudinally striate with combination of appressed setulae and erect and suberect setae; promesonotal sculpture in form of microreticulation, striolae and striae on mesopleuron, and striolae on posterodorsal surface; head orange, mesosoma, petiole and postpetiole dark brown to black, gaster bright yellow, legs brown . . . . . Monomorium flavonigrum

Figure 620.

Head capsule rectangular in full-face view (Figure 621); frons longitudinally striate and reticulate with combination of incurved decumbent and subdecumbent setulae and erect and suberect setae; promesonotal sculpture in form of microreticulation and rugosity over entire promesonotum; otherwise coloured (usually a combination of a tawny or red head and mesosoma with some brown infuscation, and dark brown or black gaster) . . . . . Monomorium longinode

Figure 621.

20

return to couplet #18

Anteromedial margin of clypeus a broadly U-shaped cleft between the median clypeal carinae, which are often produced as teeth, denticles or lobes (includes polymorphic species with disproportionately large, square heads in major caste; generally matt in appearance with rugose mesosoma) (Figure 622) . . . . . 21

Figure 622.

Anteromedial margin of clypeus either convex and protuberant, straight, slightly emarginate, or with shallow V-shaped groove (e.g. Figures 623, 624, 625); at most, median clypeal carinae (if present) produced as weak lobes or denticles (includes mainly dry and wet sclerophyll forest species, often smooth and shining in appearance) . . . . . 32

Figure 623.

Figure 624.

Figure 625.

21

return to couplet #20

Petiolar node cuboidal or nearly so, about as high as wide (Figure 626) . . . . . 22

Figure 626.

Petiolar node conical (Figure 627), cuneate (Figure 628) or tumular (Figure 629), usually tapered dorsally, but in profile always higher than wide . . . . . 25

Figure 627.

Figure 628.

Figure 629.

22

return to couplet #21

Propodeum armed with small denticles . . . . . Monomorium longiceps (in part, also see couplet couplet #28)

Propodeum unarmed . . . . . 23

23

return to couplet #22

Frons and mesosoma shining and polished in appearance with scattered foveae and striolae; distinct lateral striae present on propodeum; median clypeal carinae raised and distinct, produced as blunt lobes (Figure 630); petiolar node rugose . . . . . Monomorium xantheklemma

Figure 630.

Frons and mesosoma matt in appearance, with promesonotum, propodeum and petiole either rugose or granulose-reticulate; clypeal carinae developed as stout, incurved denticles or teeth (Figure 631) . . . . . 24

Figure 631.

24

return to couplet #23

Frons longitudinally striate; promesonotum microreticulate and rugose; red or reddish-orange; posterior promesonotum, propodeum, petiole and postpetiole strongly infuscated with black . . . . . Monomorium legulum

Frons finely granulose-microreticulate and striolate; promesonotum finely granulose-microreticulate; concolorous reddish-orange, without infuscation . . . . . Monomorium bihamatum

25

return to couplet #21

Frons densely foveate and microreticulate (Figure 632a); propodeal declivity strongly delimited anteriad by bevelled surface with well-defined anterior border (Figure 632b) . . . . . 26

Figure 632a.

Figure 632b.

Frons not foveate, propodeal declivity not as above . . . . . 27

26

return to couplet #25

Head and mesosoma without erect or semi-erect setae; colour uniformly orange . . . . . Monomorium elegantulum

Head and mesosoma with a few erect and semierect setae (Figure 633); brownish to black head and gaster, tan mesosoma (Eneabba only) . . . . . Monomorium falcatum gp. sp. JDM 1178

Figure 633.

27

return to couplet #25

Head, mesosoma and gaster covered with decumbent setulae only, erect and suberect setae lacking; small (TL ≈ 2 mm) . . . . . Monomorium pubescens

Erect and suberect setae always present on body; larger (TL > 2 mm). . . . . . 28

28

return to couplet #27

Head capsule rectangular; usually five teeth and denticles, rarely four; monomorphic; colour tawny orange or red, often with some infuscation around propodeum, petiole and postpetiole, gaster orange, appendages brown. . . . . . Monomorium longiceps (in part, also see couplet couplet #22)

Head capsule square and massive; always with four stout teeth; monomorphic, polymorphic or displaying monophasic allometry; colour variable . . . . . 29

29

return to couplet #28

Monomorphic; colour predominantly orange or red . . . . . 30

Polymorphic or displaying monophasic allometry, with considerable size range between largest and smallest workers; colour variable but black, brown, black-and-orange and black-and-red predominate . . . . . 31

30

return to couplet #29

Anteromedial margin of clypeus with two broad, longitudinally striate lobes (Figure 634a); frons longitudinally striate with erect and suberect setae, setae short (≤ width of eye); propodeum rounded, transversely striate (Figure 634b); crimson to orange . . . . . Monomorium striatifrons

Figure 634a.

Figure 634b.

Median clypeal carinae produced apically as pair of pronounced teeth; frons microreticulate and striolate with erect and suberect setae; propodeum smoothly rounded or angulate in profile or armed with small denticles or flanges, but without transverse striae; crimson to reddish orange with head, gaster and appendages darker (rare and localised in north of SWBP) . . . . . Monomorium majeri

31

return to couplet #29

Smallest minor workers dissimilar in morphology and pilosity to media and major workers; major workers rather hirsute and rugose, minor workers with shorter setae and more angulate, microreticulate propodeum; typically among major and media workers head, gaster and appendages black, dark brown or brown, mesosoma, propodeum and waist segments orange to crimson; minor workers similar in colour, or uniformly brown or dark brown; median clypeal carinae produced as single pair of lobes or denticles in major and minor workers, occasionally feebly bilobate in media workers. (Possibly a complex of two or more species is represented here.) . . . . . Monomorium rufonigrum

Morphology of minor, media and major workers similar, colouration never as above in major and media workers (usually either concolorous orange, brown or black, or brown with yellow gaster); median clypeal carinae always produced as bifurcated lobes or denticles . . . . . Monomorium bicorne

32

return to couplet #20

Viewed in profile, postpetiole a curved, horizontal cone, narrowest at its junction with petiole and widest at or near its junction with gaster (Figure 635) . . . . . Monomorium crinitum

Figure 635.

Viewed in profile, postpetiole strongly constricted both anteriad and posteriad, so that its greatest diameter is at its midpoint; postpetiolar shape round or square (Figure 636) . . . . . 33

Figure 636.

33

return to couplet #32

Subpetiolar process a broad flange ending in a spur anteriad; propodeal angles produced in the form of sharp spines (Figure 637); three larger teeth and four tiny denticles on inner mandibular edge . . . . . Monomorium sublamellatum

Figure 637.

Subpetiolar process at most a tapering, narrow flange ending in a small, anteroventral protuberance or spur; propodeal angles not produced as spines (e.g. Figure 638); maximum number of mandibular teeth and denticles five . . . . . 34

Figure 638.

34

return to couplet #33

PF 1,2; small (HML 1.25–1.75 mm); four mandibular teeth and denticles; frons of head capsule and petiolar node unsculptured, smooth and shining, propodeal angles rounded . . . . . Monomorium sordidum

PF 2,2 or 2,3; size often larger, if small with four mandibular teeth and denticles, head and petiolar node distinctly sculptured or propodeal angles acute to denticulate . . . . . 35

35

return to couplet #34

Dorsum of head and entire mesosoma finely reticulate-punctate (Figure 639); PF 2,2 (introduced orange or yellow species, only found in highly disturbed, predominantly urban environments in Australia) . . . . . Monomorium pharaonis

Figure 639.

Sculpture not as above, species generally smooth; PF predominantly 2,3 . . . . . 36

36

return to couplet #35

Frons with strong reticulate or foveate sculpture; propodeal declivity strongly delimited anteriad by oblique, bevelled surface with well-defined anterior border (Figure 640); viewed dorsally, mesosoma uniformly densely sculptured with longitudinal striae, reticulations and occasional foveae (Figure 641) . . . . . Monomorium lacunosum

Figure 640.

Figure 641.

Frons with reduced sculpture (not as above) or completely smooth and shining; propodeal declivity without distinct oblique, beveled surface with well-defined anterior border; sculpture of mesosoma not as above . . . . . 37

37

return to couplet #36

Basal tooth much broader than other pre-apical teeth (Figure 642); distinctly polymorphic, with large headed major workers having rather small eyes . . . . . Monomorium euryodon

Figure 642.

Basal tooth of same size or smaller than other pre-apical teeth; worker monomorphic or exhibiting monophasic allometry . . . . . 38

38

return to couplet #37

Frons and promesonotum with many evenly-spaced short (nearly all ≤ width of eye) erect and suberect setae (Figure 643) . . . . . Monomorium brachythrix

Figure 643.

Pilosity consisting mainly of longer erect and suberect setae (> width of eye), setation less dense . . . . . 39

39

return to couplet #38

PF 2,2; mandible with four teeth and denticles; often only three visible; propodeum unarmed (introduced species in urban or otherwise disturbed habitats) . . . . . Trichomyrmex destructor

PF 2,3; four teeth always visible, five often present; propodeum usually angulate, propodeal angles often with denticles, especially in larger workers (M. centrale, M. leae) . . . . . 40

40

return to couplet #39

Anteromedial margin of clypeus often projecting as narrow ellipse or rectangle, sometimes slightly emarginate, but never forming a shallow groove (Figure 644); clypeal denticles or lobes absent; petiolar node usually cuneate or tumular, only rarely subcuboidal or cuboidal . . . . . Monomorium leae

Figure 644.

Anteromedial margin of clypeus forming a shallow V-shaped groove between median clypeal carinae, which are developed as denticles (Figure 645); petiolar node cuboidal or subcuboidal . . . . . 41

Figure 645.

41

return to couplet #40

Eye moderate in size (eye width 0.5–1.5 x greatest width of antennal scape); head capsule nearly always darker than promesonotum in full-face view, but never lighter in colour; petiolar node higher than wide and tending to subcuboidal (Figure 646); number of mandibular teeth and denticles usually five (minute basal denticle may occasionally be lacking) . . . . . Monomorium centrale

Figure 646.

Eye large (eye width > 1.5 x greatest width of antennal scape); head capsule lighter coloured than promesonotum in full-face view; petiolar node low and cuboidal in shape (Figure 647); four mandibular teeth and denticles (very rare) . . . . . Monomorium durokoppinense

Figure 647.