Tetramorium flabellum species group

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Based on Bolton 1980

Species

The flabellum group is divided into four complexes

coloreum species complex

flabellum species complex

granulatum species complex

pylacum species complex

Identification

Diagnosis

Antennae 12-segmented. Sting appendage triangular or pennant-shaped, sometimes elongate and blunted apically. Mandibles longitudinally striate, usually coarsely so. Anterior clypeal margin entire, without a median notch or impression. Eyes small to moderate, usually in the range 0.18-0.24 x HW, rarely slightly more or less than this. Scapes variable in length, SI usually < 90 but sometimes 100 or more in flabellum-complex. Frontal carinae always extending back well beyond the level of the posterior margins of the eyes, commonly approaching the occipital margin but in some fading out roughly midway between the level of the posterior margins of the eyes and the occipital margin. Propodeal spines in profile long and strong, commonly curved or weakly sinuate along their length, always distinctly longer than the metapleural lobes, the latter triangular or dentiform. Petiole in profile nodiform, usually roughly rectangular in shape with the tergal portion slightly longer than high. (In coloreum-complex this shape modified as the dorsal and posterior faces meet in a broad curve.) Petiole node in dorsal view usually longer than broad, if only slightly so; rarely otherwise. Sculpture strong, predominantly of longitudinal rugosity or reticulate-rugulation except in granulatum-complex where dense reticulate-punctate sculpture predominates. Standing pilosity on dorsal surfaces of head and body distinct in all species except Tetramorium bellicosum (appressed), the hairs usually numerous, stout and blunted apically; rarely bizarre (Tetramorium flabellum) or short, very fine and very dense (Tetramorium granulatum). Dorsal (outer) surfaces of middle and hind tibiae with fine short decumbent to appressed pubescence.

species-complexes

The group divides up into four complexes of related species. The first three complexes discussed below are closely related, the fourth and final complex is rather more distant, not easily associated with any other group and included here for convenience as the vast majority of characters shown agree with the diagnosis of this species-group.

The flabellum-complex contains the five species Tetramorium ataxium, T. flabellum, Tetramorium geminatum, Tetramorium kestrum and Tetramorium sigillum and is characterized within the group by possession of relatively long antennal scapes (SI 90 - > 100), strongly developed sculpture and frontal carinae and a rectangular outline to the petiole node in profile. Besides these the clypeal sculpture tends to consist of a strong median carina subtended by 2-4 weaker rugulae which run diagonally on the clypeus from the posterolateral margins towards the median carina. Of the five species all but T. kestrum are restricted to the rain forest zones of West and Central Africa, but T. kestrum is widely distributed in the drier woodlands of the eastern and southern parts of the continent.

The pylacum-complex contains only Tetramorium saginatum and Tetramorium pylacum and is very closely related to the flabellum-complex, differing mainly in having shorter antennal scapes (SI 80-85) and relatively broader heads (CI 89-95) than in members of that complex where SI is 90 or more and CI ranges 84-89. Apart from this the clypeus has different sculpture, consisting of a strong median carina flanked by 2-4 weaker longitudinal carinae or longitudinal rugulae. In some respects the two members of this complex form a link between T. flabellum and its allies on the one hand and the coloreum-complex on the other, as they show clypeal sculpture characteristic of the latter but have the petiole shaped as in the former.

The three species of the coloreum-complex (Tetramorium coloreum, Tetramorium invictum, Tetramorium postpetiolatum) have longitudinal clypeal sculpture, relatively short scapes (SI 77-83) and broad heads (CI 90-95) as seen in the pylacum-complex, but have the petiole node differently constructed than in either of the foregoing complexes. In fact T. postpetiolatum is intermediate between T. pylacum and T. coloreum in this respect as its node is shaped between the low rectangular shape seen in T. pylacum and the higher, narrower node of T. coloreum (see Figs 80-82). In this last-named species and in T. invictum the dorsal and posterior faces of the node meet in a continuous curve or arc, without a posterodorsal angle. All the members of these complexes are only found in West and Central Africa.

Finally, the granulatum-complex, consisting only of the species Tetramorium bellicosum and Tetramorium granulatum which are only known from Nigeria. As stated above these two species may not belong in the flabellum-group but their basic characters lead me to include them here for the time being. Apart from the group-characters these species are characterized by their sculpture, which is dominated by a very dense, fine blanketing reticulate-puncturation on the head, alitrunk and pedicel segments. Rugular sculpture when present is very feeble and obviously secondary to the punctation. Frontal carinae are not as strongly developed as in the preceding complexes, tending to fade out on the occipital area of the head. The usual pilosity of stout, blunted standing hairs, developed throughout the rest of the group (except in T. flabellum) is not present here. Instead T. granulatum has abundant short fine pilosity everywhere and T. bellicosum has flattened, appressed hairs widely scattered on the body.

Notes

Almost all of the species included in this group are distributed within the forest zones of West and Central Africa. Only a single species (Tetramorium kestrum) occurs in the drier forests of the eastern parts of the continent.

Additional Resources

References

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