Ocymyrmex fortior

Bolton and Marsh (1989) - One of the most widespread species in southern Africa. Prins (1963) notes that in prevailingly grassy areas of the Kruger National Park, South Africa, this species (as O. weitzeckeri var. arnoldi) is quite common. He states that the ants are mainly granivorous but have also been observed capturing workers of Odontomachus troglodytes (as O. haematodes) and preying on termites. He also records that the species was found in nests of Hodotermes mossambicus, though whether as a predator or merely using the termite nest as a nest-site is not stated.

Identification
Among the species with a strongly constricted base to the gaster and a developed clypeal impression fortior is defined more by its lack of specialized characters than the possession of them. The closest related species appear to be Ocymyrmex phraxus and Ocymyrmex micans. The former has a differently shaped petiole than fortior, which is evenly rugulose dorsally on the node as opposed to the feebly or unsculptured surface seen in fortior; phraxus is also darker in colour, appearing black with a red head to the naked eye. O. micans has different cephalic structure from fortior and is also orange to orange-red in colour with a lighter yellowish gaster. (Bolton 1981)

Key to Ocymyrmex workers

Distribution based on Regional Taxon Lists
Afrotropical Region: Angola, Botswana, Namibia, South Africa, Zambia, Zimbabwe.

Biology
Marsh and Robertson have observed that workers of fortior close the nest entrance with small stones during periods of nest inactivity. Also, in Zimbabwe, fortior workers have been seen adding small stones to the crater-like nest entrance that were picked up from the around some distance away from the nest. This suggests that the crater is not just a by-product of the nest excavation but an important feature of the nest entrance. Its function is not fully understood, but its presence may facilitate the deliberate blocking of the entrance noted above. (see Bolton and Marsh, 1989)

Nomenclature

 *  fortior. Ocymyrmex weitzeckeri st. fortior Santschi, 1911g: 209 (w.) ANGOLA. Bolton, 1981b: 261 (q.m.). Raised to species and senior synonym of arnoldi (and its junior synonym abdominalis), transversus, usakosensis: Bolton, 1981b: 269. See also: Bolton & Marsh, 1989: 1296.
 * transversus. Ocymyrmex weitzeckeri st. transversus Santschi, 1911g: 209 (q., not w.) ANGOLA. Junior synonym of fortior: Bolton, 1981b: 269.
 * arnoldi. Ocymyrmex arnoldi Forel, 1913a: 138 (w.m.) ZIMBABWE. Wheeler, G.C. & Wheeler, J. 1973b: 76 (l.). Subspecies of weitzeckeri: Forel, 1913j: 213; Arnold, 1916: 197. Senior synonym of abdominalis: Arnold, 1916: 197. Junior synonym of fortior: Bolton, 1981b: 269.
 * abdominalis. Ocymyrmex weitzeckeri st. abdominalis Santschi, 1914e: 16 (w.) SOUTH AFRICA. Junior synonym of arnoldi: Arnold, 1916: 197.
 * usakosensis. Ocymyrmex weitzeckeri var. usakosensis Stitz, 1923: 146 (w.) NAMIBIA. Junior synonym of fortior: Bolton, 1981b: 269.

Worker
TL 6.7-8.2, HL 1.68-2.00, HW 1.58-1.98, CI 94-99, SL 140-1.70, SI 85-91, PW 1.04-1.22, AL 2.04-2.44 (20 measured).

Anterior clypeal margin with a semicircular median impression which is flanked on each side by a small tooth or denticle. Maximum diameter of eye 0.36-0.40, about 0.20-0.23 x HW. Promesonotal dorsum evenly shallowly convex in profile, the convex portion not strongly raised above the level of the propodeum so that the slope of the posterior half of the mesonotum is very shallow indeed. Propodeal dorsum flat or slightly sloping, rounding evenly into the declivity, the slope of which is quite steep but by no means vertical. Metapleural lobes low and bluntly rounded, sometimes mostly concealed by the bulge of the metapleural glands but usually easily visible. Peduncle of petiole commonly without a ventral process but quite frequently a low rounded bulge is present, which in a few may be shorter and more prominent, forming a broad, low and rounded angle. Petiole node small and low in profile, evenly rounded, the transition from dorsal surface of peduncle to anterior face of node involving a marked change of slope. Petiole node in dorsal view slender, small, varying from longer than broad to slightly broader than long, but the maximum width of the node usually less than the length from the petiolar spiracle to the apex of the collar where petiole and postpetiole articulate. Postpetiole in dorsal view longer than broad, sometimes only slightly so, but usually the difference easily visible. Base of first gastral tergite strongly constricted and forming a narrow neck behind the postpetiole Dorsum of head finely, densely and usually very regularly sharply longitudinally costulate, the costulae usually parallel or nearly so over most or all of the area. In many samples all costulae run straight back on the head, but commonly the outermost components tend to curve outwards behind the eyes. Very rarely there is a tendency for the costulae to converge on the midline posteriorly, in which case a few transverse members may be developed on the occipital surface. Ground-sculpture of fine punctulation is present everywhere. Dorsal alitrunk densely costulate or rugose, the usual pattern being with arched transverse sculpture on the anterior part of the pronotum followed by an area of longitudinal sculpture which runs back just beyond the mesothoracic spiracles, followed by coarser transverse sculpture on the remainder of the alitrunk dorsum. Exceptions to this are usually due to the extension of the longitudinal component on the pronotum at the expense of the transverse. At its most extreme the longitudinal component reaches forward almost to the cervical shield, and the other costulae are arched so steeply around it that they appear longitudinal everywhere except on the extreme anterior part. Very rarely the longitudinal costulae may extend back to the mesonotal-propodeal junction. In a few cases the costulae between the mesothoracic spiracles are oblique, and now and then an individual is found in which the entire dorsal alitrunk is transversely sculptured. Ventral surface of petiole with transverse rugulae of variable intensity, usually fairly distinct but grading through to very faint. These rugulae may extend for some distance up the sides of the node before fading out, but rarely reach the dorsum. Dorsum of peduncle and anterior and posterior faces of node usually with weak transverse rugulae, very faint and scratch-like in places; the dorsum of the node itself only rarely with vestiges of rugular sculpture, generally unsculptured or with a superficial patterning. Postpetiole only with a superficial patterning or more or less smooth. All dorsal surfaces of head and alitrunk with hairs of varying length, the hairs of the first gastral tergite much shorter and sparser than on the alitrunk. Head and alitrunk varying from dull brick-red to lighter red, the two always the same colour; gaster darker, blackish brown to black.

Type Material
Bolton (1981):

Syntype workers, Angola: Benguela, Cucala (J. Cruchet) (NM, Basle) [examined].

Ocymyrmex weitzeckeri, st. transversus Holotype female [not worker], Angola: Benguela, Cucala (J. Cruchet) (NM, Basle) [examined].

Ocymyrmex arnoldi Syntype workers, males, Zimbabwe: Bulawayo (G. Arnold) [examined].

Ocymyrmex weitzeckeri [sic] st. abdominalis Syntype workers, South Africa: Natal, Zululand, Entendweni, 20.viii.1905 (I. Tragardh) (NM, Basle) [examined].

Ocymyrmex weitzaeckeri [sic] var. usakosensis Syntype workers, South West Africa: Usakos, iv-vi.1911 (w. Michaelsen) (syntypes presumed lost, not in ).