Tetramorium signatum

This species nests in sandy to loamy soils, entrances sometimes with crater of soil around them. Alates were collected from nests in December. Two nests were found with Thysanura inquilines. This species has been collected by digging up nests and also from pitfall traps, yellow pan traps, tuna baits, sugar baits and cookie baits. (Mbanyana et al. 2018)

Identification
Mbanyana et al. (2018) - Tetramorium signatum is similar to Tetramorium rufescens and Tetramorium pogonion. Tetramorium pogonion is relatively smaller compared to the other two species with relatively larger eyes (OI > 30) and a different head shape. Tetramorium signatum and T. rufescens can be separated on basis of the sculpture pattern on the dorsum of mesosoma. In T. signatum, the dorsum of the mesosoma has distinct longitudinal or irregular rugulae, whereas in T. rufescens, the dorsum of the mesosoma has a dense reticulate punctation and sometimes with a few short faint longitudinal costulae.

Distribution
This species has been recorded from South Africa (Eastern Cape, Western Cape, and Northern Cape), Namibia and Angola.

Distribution based on Regional Taxon Lists
Afrotropical Region: Angola, Namibia, South Africa. Palaearctic Region: Israel.

Habitat
Known from the following ecoregions: Albany Thickets, Kalahari Xeric Savanna, Kaokoveld Desert, Knysna-Amatole Montane Forests, Montane Fynbos and Renosterveld, Nama Karoo (including Koedoesberge-Moordenaars Karoo), Namib Desert, Namibian Savanna Woodlands and Succulent Karoo.

Nomenclature

 *  signatum. Tetramorium solidum var. signatum Emery, 1895h: 35 (w.) SOUTH AFRICA. Raised to species and senior synonym of grootensis, lugubre, tuckeri: Bolton, 1980: 251.
 * lugubre. Tetramorium solidum subsp. lugubre Forel, 1910e: 425 (w.) ANGOLA. Junior synonym of signatum: Bolton, 1980: 251.
 * grootensis. Tetramorium solidum var. grootensis Forel, 1913a: 118 (q.m.) SOUTH AFRICA. Junior synonym of signatum: Bolton, 1980: 251.
 * tuckeri. Tetramorium solidum var. tuckeri Arnold, 1926: 259 (w.q.) SOUTH AFRICA. Subspecies of solidum: Prins, 1973: 5. Junior synonym of signatum: Bolton, 1980: 251.

Mbanyana et al. (2018) - The material examined matched mostly Bolton’s description, but a number of differences were noted. Interestingly, the colour variation in this species is explained by geographical distribution. It looks like there are two forms, the Karoo form and the Kalahari sand form. The specimens collected in the Karoo region mainly in South Africa are brown to black. The specimens collected from red sand dunes (Northern Cape, i.e., Dreghorn and Cullinan Farm, and parts of southern Namibia) are reddish. There is also variation in sculpture pattern. In black coloured specimens, the mesosoma has a strong irregular sculpture on the pronotum and short longitudinal striations on the mesonotum with a punctulate sculpture in between. The nodes have a punctulate sculpture overlain by irregular striations. The first gastral tergite is punctulate or shagreened at the base. Most of the reddish specimens have a strong, irregular sculpture on the pronotum and short longitudinal striations on the mesonotum with a punctulate sculpture in between. In a few specimens, the nodes are predominantly smooth with only reticulate sculpture. The spine length varies in all forms from medium, which are broad at the base, to very short. Based on that high degree of morphological variation, there is a possibility that there is more than one species within both T. signatum and T. rufescens.

Worker
TL 4.4-5.3, HL 1.20-1.36, HW 1.08-1.28, CI 89-95, SL 0.80-0.94, SI 72-75, PW 0.70-0.82, AL 1.16-1.32 (8 measured).

Mandibles longitudinally rugulose. Anterior clypeal margin with an extensive median emargination, the central portion of the margin markedly concave. Frontal carinae very short, the frontal lobes tailing off into a low ridge which runs approximately to the level of the anterior margins of the eyes before fading out or merging with the remaining cephalic sculpture. Antennal scrobes absent. Eyes large, maximum diameter 0.30-0.40, about 0.27-0.30 x HW. Propodeal spines in profile short, broad basally, usually longer than their basal width but their shape and size varying in individuals from the same nest. Metapleural lobes low and rounded. Petiole in profile strongly nodiform, in dorsal view broader than long and broader behind than in front. Postpetiole with a strongly developed ventral process on each side, the space between these two processes transversely concave so that they project freely below the node. Dorsum of head finely and quite densely costulate or longitudinally rugulose, the spaces between with only faint ground sculpture. The longitudinal sculpture tends to diverge posteriorly onto the occipital lobes but does not fade out, costulate or rugulose sculpture being present to the occipital margin. Dorsal alitrunk longitudinally finely rugulose, the spaces weakly punctulate but this ground-scupture usually stronger than that on the head. Petiole and postpetiole predominantly densely punctulate or shagreened but very often with a few feeble disorganized Tugulae present on the surface. First gastral tergite punctulate or shagreened basally, sometimes with traces of very faint costulae present. Dorsal surfaces of alitrunk, petiole, postpetiole and first gastral tergite without hairs. Elongate hairs present on gastral segments behind the first and on the first sternite. Head with hairs on clypeus and with 2-3 pairs on dorsum behind the level of the clypeus. Ventrally the head with a psammophore. Colour dark brown to blackish brown.

Mbanyana et al. (2018) - (N = 47) HL 0.885–1.249 (1.092); HW 0.875–1.219 (1.053); SL 0.708–0.934 (0.808); EL 0.266–0.344 (0.308); PH 0.393–0.590 (0.488); PW 0.570–0.816 (0.695); WL 0.944–1.328 (1.139); PSL 0.079–0.246 (0.179); PTH 0.285–0.438 (0.348); PTL 0.246–0.384 (0.319); PTW 0.275–0.471 (0.356); PPH 0.295–0.482 (0.377); PPL 0.226–0.334 (0.279); PPW 0.315–0.610 (0.437); OI 25–33 (29); CI 90–105 (96); SI 71–82 (77); DMI 55–81 (61); LMI 35–57 (43); PSLI 7–21 (16); PeNI 45–58 (51); LPeI 80–108 (92); DPeI 93–124 (112); PpNI 51–75 (63); LPpI 62–97 (74); DPpI 128–200 (157); PPI 106–132 (123).

Type Material
Mbanyana et al. (2018):

South Africa: syntype of Tetramorium solidum var. signatum Emery, 1895: 1 pinned worker, Western Cape, Matjiesfontein, E. Simon leg. (: CASENT0904841); syntypes of Tetramorium solidum var. grootensis Forel, 1913: 1 pinned queen, 1 pinned male, Eastern Cape, Willowmore, H. Brauns leg. (: CASENT0901188; : CASENT0909156).

Angola: syntype of Tetramorium solidum subsp. lugrubre Forel, 1910: 1 pinned worker, Mossamedes, de Picard leg. (MHNG: CASENT0909157).

Namibia: syntypes of Tetramorium solidum var. tuckeri Arnold, 1926: 1 pinned queen, 1 pinned worker, Brehdon, 20 Dec. 1915, R.W.E. Tucker leg. (BMNH: CASENT0901189; : SAM-ENT-0011762).

References based on Global Ant Biodiversity Informatics

 * Arnold G. 1917. A monograph of the Formicidae of South Africa. Part III. Myrmicinae. Annals of the South African Museum. 14: 271-402.
 * Arnold G. 1926. A monograph of the Formicidae of South Africa. Appendix. Annals of the South African Museum. 23: 191-295.
 * Bolton B. 1980. The ant tribe Tetramoriini (Hymenoptera: Formicidae). The genus Tetramorium Mayr in the Ethiopian zoogeographical region. Bulletin of the British Museum (Natural History). Entomology 40: 193-384.
 * Braschler B., S. L. Chown, and K. J.Gaston. 2012. The Fynbos and Succulent Karoo Biomes Do Not Have Exceptional Local Ant Richness. PLoS ONE 7(3): e31463.doi:10.1371/journal.pone.0031463
 * Emery C. 1895. Voyage de M. E. Simon dans l'Afrique australe (janvier-avril 1893). 3e mémoire. Formicides. Annales de la Société Entomologique de France 64: 15-56.
 * Forel A. 1910. Note sur quelques fourmis d'Afrique. Annales de la Société Entomologique de Belgique 54: 421-458.
 * Forel A. 1913. Fourmis de Rhodesia, etc. récoltées par M. G. Arnold, le Dr. H. Brauns et K. Fikendey. Annales de la Société Entomologique de Belgique 57: 108-147.
 * Hanrahan S. A., M. J. Steinbauer, and F. D. Duncan. 2014. Ant assemblages in a poorly sampled part of the arid Nama Karoo. African Entomology 22(2): 448453.
 * IZIKO South Africa Museum Collection
 * Izhaki I., B. Idelovich, R. Laster, and Y. Ofer. 2009. The impact of macro- vs micro environmental factors on the structure of ant communities inhabiting East-Mediterranean Aleppo pine forests. Israel Journal of Entomology 39: 129-146.
 * Mbanyana N. 2013. Taxonomy, phylogeny and biogeography of seed-harvesting ants in the Tetramorium solidum-group (Hymenoptera: Formicidae). Masters of Science in the Department of Botany and Zoology at Stellenbosch University 115 pages.
 * Mbanyana N., F. Hita Garcia, H. G. Robertson, and J. J. Le Roux. 2018. A taxonomic revision of seed harvester ants of the Tetramorium solidum group (Hymenoptera: Formicidae) in southern Africa. European Journal of Taxonomy 454: 1-59.
 * Wheeler W. M. 1922. Ants of the American Museum Congo expedition. A contribution to the myrmecology of Africa. VIII. A synonymic list of the ants of the Ethiopian region. Bulletin of the American Museum of Natural History 45: 711-1004