Nesomyrmex angulatus

Bolton (1982) - Arnold (1916: 259) noted that he only found angulatus on the trunks of trees but personal observation has shown that it also occurs in leaf litter samples and log mould. However, the species does seem to prefer to nest clear of the ground when possible, as colonies are often found in West Africa in cocoa pods which are still attached to the tree, and a sample from Malawi was collected in Swartzia pods.

Identification
It is easily identified by its yellow colour and lack of any trace of a metanotal groove or impression. Only one other species in the region lacks a metanotal groove, Nesomyrmex grisoni, but in this species the full adult colour is uniform blackish brown or black. (Bolton 1982)

Key to Nesomyrmex of southern Africa

Distribution
L. angulatus is the most widely distributed and commonest species of this genus in sub-Saharan Africa.

Distribution based on Regional Taxon Lists
Afrotropical Region: Botswana, Comoros, Djibouti, Eritrea, Ghana, Kenya, Malawi, Mozambique, Nigeria, Saudi Arabia, South Africa, Sudan, Tanzania, Zimbabwe. Malagasy Region: Mayotte, Seychelles. Palaearctic Region: Egypt, Ethiopia, Israel.

Biology
In South Africa this species has been found nesting in cavities of dead wood on trees in savanna habitats. (Mbanyana and Robertson 2008)

Nomenclature

 *  angulatus. Leptothorax angulatus Mayr, 1862: 739 (w.) EGYPT. Santschi, 1914b: 107 (q.). Combination in L. (Goniothorax): Emery, 1896g: 58 (footnote); in Nesomyrmex: Bolton, 2003: 272. Senior synonym of concolor, ilgii, latinodis: Bolton, 1982: 324. See also: Mbanyana & Robertson, 2008: 38. Current subspecies: nominal plus lybica.
 * ilgii. Leptothorax angulatus r. ilgii Forel, 1894b: 82 (w.) ETHIOPIA. Santschi, 1912c: 148 (q.). Combination in L. (Goniothorax): Wheeler, W.M. 1922a: 891. Junior synonym of angulatus: Bolton, 1982: 324.
 * latinodis. Leptothorax latinodis Mayr, 1895: 130 (w.) MOZAMBIQUE. Combination in L. (Goniothorax): Emery, 1896g: 58 (footnote). Junior synonym of angulatus: Bolton, 1982: 324.
 * concolor. Leptothorax angulatus var. concolor Santschi, 1914b: 107, fig. 15 (w.) KENYA. Emery, 1915g: 16 (q.m.). Junior synonym of angulatus: Bolton, 1982: 324.

Worker
Bolton (1982) - TL 3.1-3.8, HL 0.70-0.90, HW 0.56-0.74, CI 75-85, SL 0.50-0.66, SI 88-97, PW 0.40-0.56, AL 0.82-1.08 (65 measured).

Mandibles delicately but densely longitudinally striate, the striation usually distinct but sometimes superficial. Median clypeal lobe extensive, broad, covering the bases of the mandibles and having its anterior margin conspicuously arched-convex. Median clypeal carina fine, not strongly developed but usually discernible, only rarely the carina partially or wholly effaced. Antennal scrobes absent. Frontal carinae absent but in some the frontal lobe followed on one or both sides by a weak rugular line which runs back on the head. Maximum diameter of eyes 0.17-0.22, about 0.27-0.33 x HW and with 13 or more ommatidia in the longest row. With the head in full-face view the sides narrower in front of the eyes than behind, slightly convergent anteriorly. Sides of head behind eyes shallowly convex, slightly convergent posteriorly and meeting the occipital margin in a blunted angle. Occipital margin transverse to very shallowly concave, with a slightly projecting rim above the occipital foramen which is visible in full-face view. With the alitrunk in profile the dorsum forming a single shallowly convex to almost flat surface, without trace of a metanotal impression. Propodeum armed with a pair of triangular teeth or short broad spines of variable size. In general the teeth are about as long as their basal width and slightly upcurved, but individuals with spines longer than their basal width are fairly common. Specimens with the propodeal armament reduced to short broad teeth, where they are shorter than the basal width, are less common. Metapleural lobes low and rounded. In dorsal view the alitrunk with angulate to weakly dentate pronotal corners. Mesonotum narrower than pronotum and the sides of the propodeum diverging to the level of the spiracle and then converging to the bases of the propodeal teeth. Petiole in profile shaped as in Fig. 8, with a short anterior peduncle which has a triangular dentiform anteroventral process. Dorsal surface of peduncle with a denticulate process in front of the level of the spiracle on each side. Anterodorsal angle of node quite sharply defined, the posterodorsal angle much broader and bluntly rounded. Petiole node in dorsal view variable in shape and size. Usually the node about as broad as long, rarely slightly longer than broad but quite commonly obviously broader than long, in some cases approaching the postpetiole in width. Dorsum of head covered with a fine dense reticulate-punctulate ground-sculpture which in some samples is superficial and granular in appearance. Superimposed on this are very fine irregular rugulae which frequently form a narrow reticulum occipitally and sometimes also on the sides of the head. Dorsal surfaces of alitrunk, petiole and postpetiole with fine granular or punctulate ground-sculpture and with disorganized fine rugulae. The rugular sculpture is usually distinctive but in some individuals may be partially effaced. Base of first gastral tergite generally with a superficial reticular pattern but sometimes almost completely smooth. All dorsal surfaces of head and body with numerous short stout blunt hairs; such hairs absent from the appendages. Colour yellow, frequently with the antennal club darker.

Mbanyana and Robertson (2008) - HL 0.672–0.811, HW 0.565–0.692, HW1 0.610–0.736, CI 78–87, SL 0.487–0.613, SI 84–92, PW 0.423–0.541, ML 0.785–1.087, EL 0.169–0.197, EI 28–30 (5 of 81 measured).

Description matches that of Bolton (1982) except for few additional characters. Sculpture on the dorsum of head is not only reticulate-punctulate but also with longitudinal striations, which are well defined near the inner margin of the eyes.