Tetramorium humbloti

Specimens have been collected in a wide range of habitats, from rain to dry forest and in more open areas such as coastal scrub.

Identification
A member of the weitzeckeri species complex, which is part of the weitzeckeri species group.

Key to weitzeckeri-group species.

The following character set distinguishes Tetramorium humbloti from other species of the complex: propodeal spines long and acute (PSLI 29 - 39); mesosoma, especially pronotum, generally unsculptured, smooth and shiny; first gastral tergite without standing hairs.

This species occurs in Africa and the Malagasy region. The latter is unusual, as it is the only species of its species group to occur there. The combination of 11-segmented antennae, highly reduced sculpture and pilosity, and strongly anteroposteriorly compressed, squamiform petiole and postpetiole distinguish T. humbloti from all other Tetramorium in the Malagasy region. (Hita Garcia and Fisher 2012)

Distribution
Tetramorium humbloti is found on the African continent from South Africa to Tanzania. (Hita Garcia et al. 2010). In the Malagasy region it is present on the islands of the Comoros, Mauritius, Mayotte, Nosy Be, and Madagascar. There, most sampling localities are close to the coast in northern Madagascar, although two are situated at the southeastern coast.

Distribution based on Regional Taxon Lists
Afrotropical Region: Comoros, Kenya, Mozambique, Namibia, South Africa, Tanzania, Zambia, Zimbabwe. Malagasy Region: Madagascar, Mayotte.

Biology
In the Malagasy region Tetramorium humbloti seems to be fairly flexible in its habitat requirements. It was encountered in rainforests, tropical dry forests, littoral rainforests, coastal dunes, coastal scrubs, woodlands, disturbed forests, but also in coffee plantations and other anthropogenic habitats. This is surprising because in Africa T. humbloti appears to prefer open savannah, woodland, and other natural open habitats. (Hita Garcia and Fisher 2012)

Nomenclature

 *  humbloti. Tetramorium (Xiphomyrmex) humbloti Forel, 1891b: 154, pl. 4, fig. 12 (w.) COMORO IS. Emery, 1899f: 285 (q.). Combination in Xiphomyrmex: Emery, 1899f: 285; in Tetramorium: Bolton, 1979: 142. Senior synonym of pembensis, victoriensis: Bolton, 1980: 228. See also: Hita Garcia, Fischer & Peters, 2010b: 72; Hita Garcia & Fisher, 2012: 118.
 * pembensis. Tetramorium (Xiphomyrmex) humbloti var. pembensis Forel, 1907g: 83 (q.m.) TANZANIA. Forel, 1913a: 120 (w.). Combination in Xiphomyrmex: Wheeler, W.M. 1922a: 907. Junior synonym of humbloti: Bolton, 1980: 228; Hita Garcia & Fisher, 2012: 118.
 * victoriensis. Tetramorium (Xiphomyrmex) humblotii var. victoriensis Forel, 1913a: 120 (w.) ZIMBABWE. Arnold, 1917: 347 (q.m.). Junior synonym of humbloti: Bolton, 1980: 228; Hita Garcia & Fisher, 2012: 118.

Hita Garcia et al. (2010) - Generally, T. humbloti can be grouped together with Tetramorium bendai, Tetramorium sepultum, and Tetramorium tanaense because of obvious morphological similarities. However, the generally unsculptured mesosomal dorsum, especially on the pronotum, in T. humbloti differs strongly from the longitudinally rugose or rugulose sculpturation present in the other three species. Apart from this, the postpetiole is less strongly transverse (DPpI 183 - 207) than in T. bendai (DPpI 206 - 238). Additionally, the petiole in T. humbloti (DPeI 300 - 367) is more transverse than in T. bendai (DPeI 259 - 286) and T. sepultum (DPeI 259 - 269) while it is comparable to T. tanaense (DPeI 305 - 350). Furthermore, in T. humbloti standing hairs are generally absent from the mesosoma, only rarely up to 6 are observable, while in T. sepultum there are 14 to 16 present. In T. bendai there are usually none present and T. tanaense shows up to 8 standing hairs on the mesosoma. It has to be pointed out that the morphometric range of T. tanaense is well within the range of T. humbloti and both are morphologically very similar. The only separating character is the sculpturation on the mesosomal dorsum and it could be possible that both are conspecific in that T. tanaense is only a Kenyan variety of T. humbloti with much more developed sculpturation. Additional material from East Africa, especially from the coastal areas of Kenya and Tanzania, is necessary in order to better understand the distribution ranges and species boundaries of both species. The remaining species of the complex all possess numerous standing hairs on the first gastral tergite that easily distinguish them from T. humbloti and allied species.

Worker
Hita Garcia et al. (2010) - HL 0.733 - 0.833 (0.768); HW 0.711 - 0.822 (0.743); SL 0.522 - 0.622 (0.570); EL 0.156 - 0.211 (0.178); PW 0.528 - 0.633 (0.566); WL 0.867 - 1.000 (0.912); PSL 0.239 - 0.322 (0.260); PTL 0.083 - 0.128 (0.103); PTH 0.322 - 0.389 (0.348); PTW 0.289 - 0.378 (0.324); PPL 0.167 - 0.211 (0.189); PPH 0.350 - 0.467 (0.375); PPW 0.333 - 0.422 (0.371); CI 92 - 99 (97); SI 73 - 83(77); OI 21 - 27 (24); PSLI 29 - 39 (34); PeNI 51 - 62 (57); LPeI 25 - 32 (28); DPeI 300 - 367 (328); PpNI 59 - 68 (64); LPpI 44 - 57 (50); DPpI 183 - 207 (196); PPI 110 - 118 (113) (23 measured).

Head slightly longer than wide (CI 92 - 99). Anterior clypeal margin generally with shallow but distinct median impression. Frontal carinae strongly developed, ending distinctly before posterior margin of head. Antennal scrobe narrow, shallow, ventral margin not differentiated, not reaching posterior margin of head. Antennal scape of moderate length, not reaching posterior margin of head (SI 73 - 83). Eyes of variable size, from relatively small to large (OI 21 - 27), with 10 to 12 ommatidia in longest row. Metanotal groove weakly impressed. Propodeal spines very long, stout, and acute (PSLI 29 - 39). Propodeal lobes small, triangular, and acute. Node of petiole strongly squamiform, in dorsal view highly transverse, between 3 to 4 times wider than long (DPeI 300 - 367), in lateral view more than 3 times higher than long (LPeI 25 - 32). Postpetiole distinctly squamiform, in dorsal view around 2 times wider than long (DPpI 183 - 207); in lateral view not much thicker than petiolar node and around 1.7 to 2.2 times higher than long (LPpI 44 - 57). Mandibles distinctly longitudinally striate. Clypeus irregularly rugose, mostly longitudinally, sometimes rugo-reticulate; median ruga sometimes developed. Head with mostly longitudinal rugulation, dorsum of head with 9 to 12 widely spaced rugae between frontal carinae, often with cross-meshes and never reaching posterior margin of head. Spaces between dorsal rugae and scrobal area generally with strong reticulate-punctate ground sculpture, but sometimes weakly developed. Lateral area of mesosoma rugo-reticulate or rugose, except for smooth and shiny pronotum; dorsum of mesosoma, especially on pronotum, typically completely unsculptured, smooth and shiny, sometimes with weak superficial sculpturation on mesonotum, propodeal declivity completely unsculptured and shiny. Petiole, postpetiole and gaster completely unsculptured, smooth and shiny. Head generally with numerous fine, long, erect hairs; mesosoma, petiole, and postpetiole usually completely without hairs, rarely mesosoma with up to 3 pairs, and petiole and postpetiole with 1 to 2 pairs. First gastral tergite always without standing hairs. Antennal scapes and tibiae with appressed, fine pubescence. Coloration variable, from light reddish brown to dark brown, usually uniformly so but often gaster darker.

Type Material
Hita Garcia et al. (2010) : Syntype workers, COMOROS, Grand Comoro Is., Ngasiya, leg. L. Humblot (: CASENT0101295, CASENT0101296) [examined].

Tetramorium (Xiphomyrmex) humbloti var. pembensis Forel, 1907:82. Syntype females and males, TANZANIA, Pemba I, leg. Voeltzkow (MHNG) [examined]; Forel, 1912:120. Syntype workers, TANZANIA, Arusha Chini, 1903 (MHNG) [examined].

Tetramorium (Xiphomyrmex) humblotii var. victoriensis Forel, 1913:120. Syntype workers, ZIMBABWE, Victoria Falls, Zambezi River, 17.II.1912, leg. G. Arnold (MHNG) [examined].