Key to Malagasy Tetramorium species groups

This worker key is based on: Hita Garcia, F. and B. Fisher. 2015. Taxonomy of the hyper-diverse ant genus Tetramorium Mayr in the Malagasy region (Hymenoptera, Formicidae, Myrmicinae) – first record of the T. setigerum species group and additions to the Malagasy species groups with an updated illustrated identification key. ZooKeys. 512:121-153. doi:10.3897/zookeys.512.9860

The key is prefaced by this note: "The species group key presented here is based on the one published in Hita Garcia & Fisher (2011). Although the key in that publication still works for most species in Madagascar, it does not accommodate them all. The recent revisions of most species groups, with the establishment of some new groups (Hita Garcia & Fisher, 2012a, 2012b, 2014b), require an updated and improved key. The following key applies to the 19 groups we currently recognise, which contain around 125 species (the T. ranarum and T. simillimum groups will be revised in a future publication and the species count for these two groups is temporary)."

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 * Tetramorium species groups (species lists, group diagnoses, distributions, etc.)
 * Tetramorium

1

 * Species with distinctly branched hairs, usually a mixture of simple, bifid, and trifid hairs (Fig. 2A, B) . . . . . T. obesum group


 * Species without branched hairs, hairs present neither bifid nor trifid, either with simple pilosity (Fig. 2C), or with reduced pilosity but short appressed pubescence (Fig. 2D) . . . . . 2

2
return to couplet #1
 * Antennae 12-segmented (Fig. 3A); sting appendage triangular to dentiform, acute apically (Fig. 3B) . . . . . 3
 * Antennae 11-segmented (Fig. 3C); sting appendage spatulate, broadened apically (Fig. 3D) . . . . . 7

3
return to couplet #2
 * Anterior clypeal margin with distinct median impression (Fig. 4A) . . . . . T. bicarinatum group


 * Anterior clypeal margin always entire and convex, never with distinct median impression (Fig. 4B, C) . . . . . 4

4
return to couplet #3


 * Propodeum armed with long to extremely long spines (PSLI 30–49), at least 2 to 3 times longer than metapleural lobes (Fig. 5A) . . . . . T. tosii group


 * Propodeum either unarmed (Fig. 5B), armed with small triangular teeth or denticles, or armed with medium-sized spines (Fig. 5C), propodeal spines at most only as long or weakly longer than metapleural lobes, more often propodeal spines distinctly shorter than metapleural lobes . . . . . 5

5
return to couplet #4
 * Lateral portion of clypeus prominent, raised to a tooth or denticle in full-face view (Fig. 4B); propodeal spines medium-sized and spinose, approximately of same length as metapleural lobes (Fig. 5C) . . . . . T. sericeiventre group


 * Lateral portion of clypeus never modified as above (Fig. 4C); propodeum either unarmed (Fig. 5B) or armed with small triangular teeth or denticles that are shorter than metapleural lobes (Fig. 6E, F) . . . . . 6

6
return to couplet #5
 * Head in full-face view relatively thin (CI < 80) and antennal scapes very long (SI > 120) (Fig. 6A); in general appearance head, antennae, and legs elongate and slender (Fig. 6E) . . . . . T. setigerum group


 * Head in full-face view relatively thicker (CI > 85) and antennal scapes conspicuously much shorter (SI < 92) (Fig. 6B, C, D); in general appearance more compact species with thicker heads and shorter antennae and legs (Fig. 6F) . . . . . T. simillimum group

7
return to couplet #2
 * Petiolar node and postpetiole strongly squamiform, petiolar node with anterior and posterior faces parallel and well developed, straight dorsum; petiole and postpetiole always completely unsculptured, smooth, and shining; standing pilosity scarce or absent on dorsal mesosoma and waist segments, first gastral tergite without standing pilosity (Fig. 7A) . . . . . T. weitzeckeri group


 * Character combination never as above; petiole and postpetiole variably shaped, especially postpetiole never squamiform as above (Fig. 7B, C, D, E, 8C, D); if petiole squamiform and postpetiole weakly squamiform, then petiolar dorsum reduced and strongly tapering backwards posteriorly (Fig. 7F) . . . . . 8

8
return to couplet #7
 * Pronotum anterodorsally with distinct protuberance or bulge (Fig. 8A, B) . . . . . T. bonibony group (in part)


 * Pronotum anterodorsally without any protuberance or bulge (Fig. 8C, D) . . . . . 9

9
return to couplet #8
 * First gastral tergite with strongly appressed pubescence of varying length and without any standing hairs (Fig. 9A, B), or with short appressed to erect pilosity without any long, erect to suberect hairs (Fig. 9C) . . . . . 10


 * First gastral tergite usually with long, erect to suberect pilosity (Fig. 9D, E, F) . . . . . 17

10
return to couplet #9
 * Antennal scrobes well developed with sharply defined posterior and ventral margins (Fig. 10A, B) . . . . . T. ranarum group (in part)


 * Antennal scrobes usually weakly developed, never with well-defined posterior and ventral margins (Fig. 10C, D, E) . . . . . 11

11
return to couplet #10
 * In profile petiolar node rectangular nodiform with sharply angled anterodorsal and posterodorsal margins; both waist segments strongly sculptured (Fig. 11A, B) . . . . . 12


 * Petiolar node rectangular nodiform with conspicuously rounded anterodorsal and/or posterodorsal margins (Fig. 11C), high rounded nodiform (Fig. 11D), or squamiform and strongly anteroposteriorly compressed (Fig. 11E); waist segments usually completely unsculptured, smooth, and shining, rarely with very weak (Fig. 11D, E), superficial sculpture (Fig. 11C) . . . . . 13

12
return to couplet #11
 * Propodeum armed with short to moderately long spines (PSLI 18–25); dorsum of head and mesosoma without any standing pilosity (Fig. 12A, B) . . . . . T. ranarum group (in part)


 * Propodeum armed with very long spines (PSLI 50–53); dorsum of head and mesosoma with standing pilosity (Fig. 12C) . . . . . T. tortuosum group (in part)

13
return to couplet #11
 * Larger species (HW 0.82–1.03; WL 1.14–1.48); mesosoma comparatively long and slender (LMI 35–37) without distinct margination between lateral and dorsal mesosoma; propodeal spines always very long (PSLI 38–43); body colouration always dark brown to black (Fig. 13A) . . . . . T. severini group


 * Character combination never as above, especially mesosoma either with strong margination between sides and dorsum (Fig. 13B, C, E, F) or relatively shorter, high, and compact (Fig. 13D); usually much smaller species (HW 0.43–0.87; WL 0.54–1.22) with almost always brighter body colour, but if body size in range of above, then either mesosoma clearly higher and more compact (LMI 42–49) (Fig. 13D) or propodeal spines/teeth much shorter (PSLI 12–28) (Fig. 13B) . . . . . 14

14
return to couplet #13
 * Dorsum of mesosoma generally completely unsculptured (Fig. 14A), very rarely with few superficial, weak rugulae laterally, but median area of promesonotum always unsculptured and shiny (Fig. 14B, C); mandibles always conspicuously sculptured . . . . . 15


 * Mesosoma usually strongly sculptured (Fig. 14E, F), very rarely with weak rugulose sculpture including median area of promesonotum (Fig. 14D), but then mandibles completely unsculptured and very smooth and shiny . . . . . 16

15
return to couplet #14
 * Propodeal spines long and metapleural lobes short (Fig. 15A); petiolar node in dorsal view distinctly wider than long (Fig. 15B) . . . . . T. bessonii group (in part)


 * Propodeal spines/teeth comparatively short and metapleural lobes of almost similar size (Fig. 15C); petiolar node in dorsal view longer than wide (Fig. 15D) . . . . . T. tsingy group

16
return to couplet #14
 * Mandibles always unsculptured, smooth, shining (Fig. 16A, B); waist segments always without long, erect to suberect pilosity (Fig. 16E, F) . . . . . T. schaufussii group (in part)


 * Mandibles variably sculptured (Fig. 16D, D); waist segments usually with long, erect to suberect pilosity (Fig. 16G); if pilosity absent (Fig. 16H), then mandibles conspicuously sculptured (Fig. 16D) . . . . . T. naganum group (in part)

17
return to couplet #9
 * Antennal scrobes very well developed and distinctly impressed with sharply defined posterior and ventral margins; scrobes with very conspicuous median longitudinal scrobal carina, carina always ending between posterior eye margin and posterior margin of scrobe (Fig. 17A, C); petiolar node in dorsal view always noticeably broader than long (Fig. 17B), and in profile with more or less rounded antero*and posterodorsal margins (Fig. 17C); dorsal mesosoma with longitudinally rugose sculpture (Fig. 17B); all dorsal surfaces of body with abundant, usually dense, long, and suberect to erect hairs (Fig. 17C) . . . . . T. plesiarum group


 * Character combination never as above; usually antennal scrobes either almost absent (Fig. 17D, E) to weakly developed (Fig. 17F), or moderately developed and distinctly impressed, but without sharply defined posterior and ventral margins or a strong median longitudinal carina (Fig. 17G); if antennal scrobes well developed with sharp margin all around and median scrobal carina developed (Fig. 17H, I), then either dorsum of mesosoma reticulate-rugose (Fig. 17J) and/or petiolar node in profile rectangular nodiform with sharply angled anterio- and posterodorsal margins (Fig. 17K) . . . . . 18

18
return to couplet #17
 * Sculpture on head, mesosoma, and waist segments strongly reduced: head usually very weakly sculptured (especially posteriorly) (Fig. 18A, B, C, D), dorsum of mesosoma generally completely unsculptured (Fig. 18K), very rarely with very few weak, superficial rugulae laterally (Fig. 18L), and waist segments always completely unsculptured . . . . . 19


 * Sculpture never as strongly reduced as above, head always and to a great extent sculptured (Fig. 18E, F, G, H, I, J), dorsum of mesosoma always completely sculptured, (Fig. 18M, N), and waist segments variably sculptured . . . . . 20

19
return to couplet #18
 * Mesosoma only weakly marginate between lateral and dorsal mesosoma, instead sides of mesosoma generally rounding more or less smoothly onto the dorsum (Fig. 19A), mesosoma also relatively high and compact (LMI 43–48); mesosoma and first gastral tergite with relatively dense, short to moderately long, appressed to decumbent pubescence intermixed with relatively scarce, much longer erect pilosity (Fig. 19A) . . . . . T. bessonii group (in part)


 * Mesosoma usually with strong margination between lateral and dorsal mesosoma (Fig. 19B), but if mesosoma less marginate (Fig. 19C), then generally more elongate and slender (LMI 37–42); mesosoma and first gastral tergite with few to abundant long, standing hairs, often mixed with substantially fewer and (mostly) shorter appressed to subdecumbent pilosity, pubescence very scarce to absent (Fig. 19B, C) . . . . . T. marginatum group (in part)

20
return to couplet #18
 * Relatively large species (HW 0.85–0.97; WL 1.21–1.48); SI relatively high (SI 89–104); propodeal spines very long to extremely long (PSLI 35–68); petiolar node in profile clublike, elongate and longer than high, posterodorsal angle situated higher than anterodorsal (Fig. 20A, B); dorsum of mesosoma conspicuously reticulate-rugose (Fig. 20H); whole body covered by numerous very long, fine, standing hairs (Fig. 20A, B) . . . . . T. kelleri group


 * Character combination never as above, most species much smaller with lower SI and shorter propodeal spines, a differently shaped petiolar node, and with less abundant and shorter pilosity (Fig. 20C, D, E); if species in size range of above and with similarly long propodeal spines and dense, long pilosity, then SI usually lower (SI 65–93), petiolar node more or less rectangular nodiform, and dorsum of mesosoma longitudinally rugose (Fig. 20F, G, I) . . . . . 21

21
return to couplet #20
 * Mesosomal outline in profile relatively flat, comparatively low and elongated (LMI 35–39) (Fig. 21A, B, C); in profile petiolar node rounded nodiform to high rounded nodiform with well-rounded margins (Fig. 21A, B), rarely high cuneiform or squamiform (Fig. 21C); propodeum usually with short teeth/denticles and rarely with spines of moderate length (PSLI 7–25, usually below 20); mandibles and waist segments always unsculptured, smooth and shining (Fig. 21A, B, C) . . . . . T. schaufussii group (in part)


 * Character combination never as above; mesosoma usually more compact and higher (LMI usually conspicuously above 40, very rarely below) (Fig. 21D, E, F, G, H), if LMI < 40, then propodeal spines long to very long (PSLI 27–72, usually above 35) and waist segments weakly to conspicuously sculptured (Fig. 21I) . . . . . 22

22
return to couplet #21
 * Mesosoma strongly marginate from sides to dorsum (Fig. 21G); dorsum of promesonotum weakly (irregularly) longitudinally rugulose with few, larger unsculptured patches medially, propodeal dorsum either fully unsculptured or only partly irregularly rugulose (Fig. 22A, B); both waist segments always completely unsculptured, smooth and shiny; body colour uniformly yellow (Fig. 21G) . . . . . T. marginatum group (in part)


 * Character combination never as above, especially dorsum of mesosoma usually with conspicuous sculpture along its entire length (Fig. 22C, D, E, F) . . . . . 23

23
return to couplet #22
 * Petiolar node in profile dorsally conspicuously anteroposteriorly compressed and strongly narrowing towards apex, giving node a triangular or sharply cuneiform appearance; both waist segments always completely unsculptured, smooth and shiny (Fig. 23A, B, C, D) . . . . . 24


 * Petiolar node variably shaped: rectangular nodiform (Fig. 23E), high nodiform (Fig. 23F), squamiform (Fig. 23G), or broadly/weakly cuneiform (Fig. 23H), in the latter case node not strongly narrowing dorsally and petiole and/or postpetiole distinctly sculptured (Fig. 23H) . . . . . 25

24
return to couplet #23
 * Dorsum of mesosoma longitudinally rugose/rugulose (Fig. 24A, B) . . . . . T. dysalum group (in part)


 * Dorsum of mesosoma conspicuously reticulate-rugose, especially anteriorly (Fig. 24C, D, E, F) . . . . . T. bonibony group (in part)

25
return to couplet #23
 * Dorsum of mesosoma conspicuously reticulate-rugose throughout its length (Fig. 25A, B, C); petiolar node either squamiform, unsculptured, smooth, and shining or nodiform and usually conspicuously sculptured (Fig. 26A, B, C) . . . . . 26


 * Dorsum of mesosoma longitudinally rugose/rugulose (Fig. 25D, E), sometimes irregularly arranged but still conspicuously longitudinal in nature (Fig. 25F), if the latter, then petiolar node never as above (Fig. 27A, B, C, D, E, F, G, H) . . . . . 27

26
return to couplet #25
 * Eyes relatively large (OI 25–26); petiolar node in profile distinctly squamiform and anteroposteriorly compressed (Fig. 26A); waist segments always completely unsculptured, smooth, and shining (Fig. 26A) . . . . . T. dysalum group (in part)


 * Eyes smaller than above, usually significantly so; petiolar node weakly cuneiform to rectangular nodiform and variably sculptured (Fig. 26B, C), but never squamiform and unsculptured as above (Fig. 26B, C) . . . . . T. ranarum group (in part)

27
return to couplet #25
 * Petiolar node usually rectangular nodiform with more or less sharply angled anterodorsal and posterodorsal margins (Fig. 27A, B, C), if petiolar node weakly cuneiform (Fig. 27D), then base of first gastral tergite sculptured, at least weakly so; both waist segments always distinctly sculptured, usually distinctly rugose, rarely rugulose (Fig. 27A, B, C, D) . . . . . T. tortuosum group (in part)


 * Petiolar node usually squamiform (Fig. 27E, F), high rounded nodiform (Fig. 27G) or weakly cuneiform (Fig. 27H), if petiolar node weakly cuneiform, then first gastral tergite completely unsculptured, smooth, and shining; petiole and postpetiole fully unsculptured, smooth, and shiny in most species (Fig. 27E, F, G), a few species with one or both waist segments conspicuously sculptured (Fig. 27H) . . . . . 28

28
return to couplet #27
 * Pilosity and pubescence on first gastral tergite usually consisting of abundant, long, erect to suberect hairs on top of scarce, much shorter, appressed to decumbent pubescence (Fig. 28A, 28B, 28C), very rarely with long decumbent to subdecumbent pilosity on top of scarce appressed pubescence (Fig. 28D) . . . . . T. dysalum group (in part)


 * Pilosity and pubescence on first gastral tergite variable: either with few moderately long, appressed to decumbent pubescence in combination with several much longer, fine, and erect hairs (Fig. 28E), or with a mix of short to moderately long, abundant, decumbent to suberect pilosity, pilosity appearing disorganized due to varying degrees of inclination and hair length (Fig. 28F, G), or with short, abundant, subdecumbent to suberect pilosity, and without any appressed to decumbent pubescence or long, fine erect hairs (Fig. 28H) . . . . . T. naganum group (in part)