Polyrhachis schistacea

P. schistacea is a common savannah and scrub forest species which ranges from Sudan to South Africa and from the east to the west coasts of the continent south of the Sahara, but it is absent from rain forest, where it is apparently replaced by Polyrhachis militaris. Nests are constructed in the earth either in open ground where a crater is formed around the entrance, or under stones. More rarely the species nests in or under decayed wood. Foraging is carried out on the surface of the ground, on grass stems and on low bushes. Arnold (1924:745) states that the entrance to the nest, when made directly into the ground is “surrounded by an irregular, cup-like wall about one to one and a half inches high, made of woven pieces of grass blades”. He also notes that the ant tends aphids and coccids, one of the few food records for the genus in the Ethiopian region. (Bolton 1973)

Identification
A member of the Polyrhachis militaris species-group. Bolton (1973) - Most of the many synonyms of this species represent variability in a range of characters such as hair colour, density of pilosity, intensity of sculpturation or differences in sculptural details, convexity of eyes, or on size and relative proportions of constituent parts of the alitrunk. The present study has shown these to be gradient factors, at times even with variation in the same nest series. Eye convexity also varies from nearly flat through to strongly convex.

Distribution based on Regional Taxon Lists
Afrotropical Region: Angola, Cameroun, Congo, Democratic Republic of Congo, Equatorial Guinea, Ethiopia, Gabon, Guinea, Ivory Coast, Kenya, Malawi, Mozambique, Nigeria, Sierra Leone, Somalia, South Africa, Sudan, Togo, Uganda, United Republic of Tanzania, Zimbabwe.

Biology
Alate females have been recorded as follows, Uganda : August, November. Kenya: February. Malawi: March. Rhodesia: January. (Bolton 1973)

Nomenclature

 * carinatus. Polyrhachis carinatus Smith, F. 1858b: 71, pl. 4, figs. 48, 49 (w.) SOUTH AFRICA. [Junior secondary homonym of carinata Fabricius, above.] Senior synonym of rugulosus: Emery, 1896d: 379; hence the latter is first available replacement name for this taxon: Bolton, 1995b: 345.
 *  schistacea. Hoplomyrmus schistaceus Gerstäcker, 1859: 262 (w.) MOZAMBIQUE. [Also described as new by Gerstäcker, 1862: 508.] Forel, 1907a: 38 (q.). Combination in Polyrhachis: Mayr, 1863: 446; in P. (Myrma): Santschi, 1914b: 140. Subspecies of militaris: André, 1887: 288. Revived status as species: Dalla Torre, 1893: 268; Forel, 1907a: 38; Wheeler, W.M. 1922a: 1000; Arnold, 1924: 742; Bolton, 1973b: 318. Senior synonym of atrociliata, divina, divinoides, fracta, gagatoides, rugulosus (and its junior synonyms cafrorum, carinatus) and material of the unavailable names beguelensis, mediopilosa, subplana referred here: Bolton, 1973b: 318.
 * rugulosus. Polyrhachis rugulosus Mayr, 1862: 685, pl. 19, fig. 7 (w.) SOUTH AFRICA. Arnold, 1924: 744 (q.). Junior synonym of, and hence first available replacement name for, carinatus Smith, F. 1858b: 71 [Junior secondary homonym of Formica carinata Fabricius, 1804: 413.]: Emery, 1896d: 379; Wheeler, W.M. 1922a: 1002. Combination in P. (Myrma): Santschi, 1914b: 141. Subspecies of militaris: Mayr, 1893: 197; of schistacea: Stitz, 1910: 151; Wheeler, W.M. 1922a: 1002; Arnold, 1924: 744. Senior synonym of cafrorum: Mayr, 1893: 197; Forel, 1894b: 72. Junior synonym of schistacea: Bolton, 1973b: 318.
 * cafrorum. Polyrhachis militaris r. cafrorum Forel, 1879a: 120 (w.q.m.) SOUTH AFRICA. Raised to species: Dalla Torre, 1893: 260. Junior synonym of rugulosus: Mayr, 1893: 197; Forel, 1894b: 72.
 * atrociliata. Polyrhachis (Myrma) schistacea st. atrociliata Santschi, 1913c: 314 (w.) DEMOCRATIC REPUBLIC OF CONGO. [Also described as new by Santschi, 1914b: 141.] Raised to species: Santschi, 1933b: 108. Junior synonym of schistacea: Bolton, 1973b: 318.
 * divina. Polyrhachis schistacea var. divina Forel, 1913b: 348 (in text) (w.) TANZANIA. Combination in P. (Myrma): Santschi, 1914b: 141. Junior synonym of schistacea: Bolton, 1973b: 318.
 * gagatoides. Polyrhachis (Myrma) schistacea var. gagatoides Santschi, 1913c: 314 (w.) CONGO. [Also described as new by Santschi, 1914b: 142.] Junior synonym of schistacea: Bolton, 1973b: 318.
 * fracta. Polyrhachis (Myrma) schistacea st. fracta Santschi, 1914b: 141 (w.) KENYA. Junior synonym of schistacea: Bolton, 1973b: 318.
 * divinoides. Polyrhachis schistacea var. divinoides Arnold, 1924: 744 (w.) DEMOCRATIC REPUBLIC OF CONGO. [First available use of Polyrhachis schistacea r. rugulosa var. divinoides Forel, 1913b: 348; unavailable name.] Junior synonym of schistacea: Bolton, 1973b: 318.

Worker
Bolton (1973) - TL 9.3-13.7, HL 2.15-2.78, HW 1.63-2.26, CI 76-80, SL 2.78-3.40, SI 141-170, PW 1.29-1.89, MTL 3.07-3.89. (30 measured.)

Anterior clypeal margin entire. In profile the clypeus is usually convex above and concave below, the anterior margin projecting as a weak shelf over the basal borders of the mandibles. Eyes virtually flat to strongly convex; the sides of the head in front of the eyes gently convex, occipital margin distinctly so. Alitrunk marginate throughout its length, the marginations sharp but not flange-like or lamellate, nor distinctly projecting upwards or outwards from the dorsum; interrupted at the sutures. Pronotal spines long and acute, usually with a narrow base. Propodeal teeth of variable length, usually small and upcurved. Pronotal suture distinct; metanotal groove impressed. Petiole with a pair of long dorsal spines and a pair of laterally placed teeth.

Erect hairs numerous, usually present on all surfaces, always present on the side of the head between the eye and the ventrolateral border and on the mesonotal and propodeal dorsa. Colour of hairs varies from white to black. Pubescence usually greyish and dense but never so dense as to mask the underlying sculpturation. In some the pubescence is very much reduced. Sculpture variable, may be of a fine reticulo-rugulation, a disoriented mass of small rugae, or a fine dense longitudinal rugulation on the dorsal surfaces of the head and alitrunk. Gastral sculpturation varying from finely reticulate to finely reticulate-punctate. If the gaster is finely reticulate the rims of the reticulae are raised and not merely superficial as in gagates. Colour uniform black, or with the legs black-brown. Usually dull, occasionally with the gaster polished.

Queen
Bolton (1973) - Answers to the above description with the usual differences associated with this caste.

Type Material
Bolton (1973) - Holotype worker, MOZAMBIQUE (probably in ).

References based on Global Ant Biodiversity Informatics

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