Polyrhachis viscosa

Identification
Rigato (2016) - A viscosa-group species with a uniquely (among all African Polyrhachis) apically enlarged scape and proximally flattened first funicular joint.

I often found specimens of P. omissa labelled as P. viscosa and mixed with it, but omissa always lacks the distinctive antennal features that separate viscosa from all other African Polyrhachis. Polyrhachis viscosa has a strongly widened apex of the scape and a strongly depressed first funicular joint (see Fig. 22 in Bolton, 1973). This feature is unique to viscosa and seemingly constant. Although I found several gynes assignable to P. omissa collected in Yemen, Collingwood and Agosti (1996) in their survey of Arabian ants mentioned P. viscosa and Polyrhachis lacteipennis only. Polyrhachis lacteipennis superficially recalls viscosa and omissa, but belongs to the non-African subgenus Myrmhopla and has a slender and immarginate mesosoma and other very distinctive features.

The main features separating omissa from viscosa workers can be summarized as follows:

Distribution based on Regional Taxon Lists
Afrotropical Region: Burkina Faso, Democratic Republic of Congo, Eritrea, Ethiopia, Ghana, Kenya, Malawi, Nigeria, Somalia, South Africa, Sudan, Uganda, United Republic of Tanzania, Zimbabwe.

Nomenclature

 *  viscosa. Polyrhachis viscosus Smith, F. 1858b: 71, pl. 4, fig. 41 (w.) SOUTH AFRICA. Combination in P. (Myrma): Santschi, 1914b: 143. Senior synonym of antinorii: Dalla Torre, 1893: 271; of imatongica, spretula: Bolton, 1973b: 330. See also: Arnold, 1924: 749.
 * antinorii. Polyrhachis antinorii Emery, 1877b: 365, fig. (w.) ETHIOPIA. Junior synonym of viscosa: Dalla Torre, 1893: 271.
 * spretula. Polyrhachis (Myrma) viscosa var. spretula Santschi, 1923e: 294 (w.q.) DEMOCRATIC REPUBLIC OF CONGO. Junior synonym of viscosa: Bolton, 1973b: 330.
 * imatongica. Polyrhachis (Myrma) cubaensis subsp. imatongica Weber, 1943c: 388, pl. 16, fig. 22 (w.) SUDAN. Junior synonym of viscosa: Bolton, 1973b: 330.

Worker
Rigato (2016) - (n=16): HL 1.58–1.87, HW 1.30–1.59, CI 79–86, SL 1.70–2.15, SI 125–142, FW 0.40–0.50, FI 30–35, PW 1.11–1.47, WL 1.97–2.50, HTL 1.66–2.20.

Type Material
Rigato (2016) - Holotype worker, SOUTH AFRICA: Natal, Durban [not seen].