Key to Malagasy Tetramorium species groups

This key is based on: Hita Garcia and Fisher. 2011. The ant genus Tetramorium Mayr (Hymenoptera: Formicidae) in the Malagasy region – introduction, definition of species groups, and revision of the T. bicarinatum, T. obesum, T. sericeiventre and T. tosii species groups. Zootaxa. 3039: 1-72.

The key is for workers and includes this caveat: "The following key was developed on the basis of existing species groups (Bolton, 1979), with significant additions and modifications made in order to incorporate a substantial amount of new material. However, it should be noted that this key is only of preliminary nature, and that the ongoing revision of all species groups might lead to further changes."

1

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


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

2
return to couplet #1
 * Antennae 11-segmented . . . . . 3
 * Antennae 12-segmented . . . . . 12

3
return to couplet #2
 * Mesosoma anterodorsally with distinct protuberance or bulge (Fig. 3.A); sculpturation on posterior head and anterior mesosoma, especially pronotum, always strongly reticulate-rugose . . . . . New species group 1 group (in parts)


 * Mesosoma anterodorsally without any protuberance or bulge (Fig. 3.B); sculpturation on posterior head and anterior mesosoma variable, but only rarely reticulate-rugose, usually with reduced sculpturation or longitudinal rugae/rugulae . . . . . 4

4
return to couplet #3


 * Both waist segments generally without any trace of rugose, rugulose, or reticulate sculpturation, generally unsculptured (Figs. 4.A, 4.B) . . . . . 5


 * One or both waist segments with conspicuous rugose, rugulose, or reticulate sculpturation (Figs. 4.C, 4.D) . . . . . 10

5
return to couplet #4
 * Both, petiolar node and postpetiole strongly squamiform and anteroposteriorly compressed (Fig. 5.A) . . . . . T. weitzeckeri group


 * Petiolar node variably shaped but postpetiole never strongly squamiform (Fig. 5.B) . . . . . 6

6
return to couplet #5


 * Petiolar node rounded high nodiform, rarely antero-posteriorly compressed; anterior and posterior faces of the node roughly parallel and all sides rounding smoothly onto the dorsal face; propodeal spines usually short to very short, very rarely otherwise (Fig. 6.A) . . . . . 7


 * Petiolar node variably shaped, usually distinctly higher and wider than long, anterior and posterior faces never parallel, in lateral view generally roughly to strongly triangular and strongly antero-posteriorly compressed dorsally, dorsum usually tapering strongly downwards posteriorly, in dorsal view strongly transverse; propodeal spines generally long and spinose (Fig. 6.B) . . . . . 8

7
return to couplet #6


 * Large, elongate species with very long and spinose propodeal spines (Fig. 7.A); mesosomal sculpturation, especially on the dorsum, weak but still present . . . . . T. severini group


 * Generally smaller, more compact species with very short to medium-sized propodeal spines or teeth (Fig. 7.B); mesosoma always distinctly sculptured, usually longitudinally rugose . . . . . T. schaufussii group

8
return to couplet #6


 * First gastral tergite either without any standing hairs, only with short to relatively long, appressed to decumbent pubescence, or with medium-sized appressed to decumbent pubescence intermixed with relatively few erect hairs (Figs. 8.A, 8.B); sculpturation on head and mesosoma highly reduced . . . . . T. bessonii group


 * First gastral tergite always with standing hairs, usually a mixture of mostly long, erect hairs with substantially fewer shorter, appressed to decumbent hairs (Figs. 8.C, 8.D); sculpturation on head and mesosoma variable . . . . . 9

9
return to couplet #8


 * Anterior face of mesosoma usually well-developed and anterodorsal angle distinct (Fig. 9.A); dorsum of mesosoma, especially on pronotum, with strong reticulate-rugose sculpturation; colouration variable . . . . . New species group 1 (in parts)


 * Anterior face of mesosoma not well-developed and anterodorsal angle absent, generally with a very short anterior portion rounding smoothly onto the dorsum (Fig. 9.B); either species dark brown to black and with almost reduced sculpturation on mesosomal dorsum, or species yellow to brown with weak irregular sculpturation on mesosomal dorsum . . . . . T. marginatum  group

10
return to couplet #4


 * Frontal carinae never running to posterior head margin, generally ending between posterior eye margin and posterior head margin, though closer to posterior eye margin, often curving down ventrally and forming posterior margin of antennal scrobe; propodeal spines always short to medium-sized and elongate-triangular to triangular (Fig. 10.A) . . . . . T. ranarum group


 * Frontal carinae usually running back to posterior head margin or ending shortly before; propodeal spines always long and spinose (Fig. 10.B) . . . . . 11

11
return to couplet #10
 * Petiolar node distinctly higher than long and usually weakly to distinctly wider than long; node in profile antero-posteriorly compressed, squamiform to high nodiform; sculpturation on both waist segments often weakly developed but generally present (Fig. 11.A) . . . . . T. dysalum group


 * Petiolar node generally longer than high, only rarely roughly as long as high or weakly higher than long, node never antero-posteriorly compressed, generally rectangular nodiform and rarely clublike; both waist segments distinctly sculptured (Fig. 11.B, 11.C) . . . . . T. tortuosum group

12
return to couplet #2


 * Anterior clypeal margin with distinct median impression (Fig. 11.A) . . . . . T. bicarinatum group
 * Anterior clypeal margin always entire and convex, never with distinct median impression (Fig. 12.B, 12.C) . . . . . 13

13
return to couplet #12


 * Propodeum armed with long to extremely long spines, at least 2 to 3 times longer than propodeal lobes (Fig. 13.A) . . . . . T. tosii group
 * Propodeum either unarmed, armed with small triangular teeth or denticles, or armed with medium-sized spinose spines, propodeal spines at most only as long or weakly longer than propodeal lobes, more often propodeal spines distinctly shorter than propodeal lobes (Fig. 13.B, 13.C) . . . . . 14

14
return to couplet #13


 * Lateral portion of clypeus prominent, raised to a tooth or denticle in full-face view (Fig. 14.A); propodeal spines medium-sized and spinose, roughly of same length as propodeal lobes . . . . . T. sericeiventre group


 * Lateral portion of clypeus never modified as above (Fig. 14.B); propodeal spines usually strongly reduced to small triangular teeth or denticles that are shorter than propodeal lobes . . . . . T. simillimum group