Plectroctena mandibularis

This species is a specialized predator of millipedes.

Distribution based on Regional Taxon Lists
Afrotropical Region: Angola, Botswana, Cameroun, Democratic Republic of Congo, Ethiopia, Kenya, Malawi, Mozambique, Namibia, Rwanda, South Africa, Uganda, United Republic of Tanzania, Zambia, Zimbabwe.

Biology
Colonies have less than 300 workers and one ergatoid queen (Villet 1990). Ergatoid queens have been observed to mate away from natal nests, after which they presumably founded a colony independently. Solitary queens with eggs and larvae were found under rocks (Villet 1999). In one such incipient nest, a dismembered milipede is evidence that foundresses hunt outside the nest. Ergatoid queens are typically associated with colony fission in ants, thus non-claustral independent colony foundation in P. mandibularis is unusual.

Workers lay trails with their stings while foraging, but these appear to be for personal orientation, because they never recruited nestmates to prey. However, workers laid trails when recruiting nestmates to new nest sites (Wilkins et al. 2006).

Foraging parties of 10-15 workers left nests and headed towards a particular area: they were led by one individual laying a trail on the ground. After a party broke up, the workers searched, captured and retrieved prey singly (Peeters & Crewe 1988).

Castes
The single ergatoid queen is not easily distinguished from nestmate workers, based on body size and slight anatomical differences.

Nomenclature

 *  mandibularis. Plectroctena mandibularis Smith, F. 1858b: 101, pl. 7, figs. 1-5 (m., ergatoid q., not w.) SOUTH AFRICA. Forel, 1913a: 108 (w.); Arnold, 1915: 86 (w.). Material of the nomen nudum caffra referred here: Roger, 1861a: 41. Senior synonym of major: Emery, 1899e: 469; Bolton, 1974c: 330; of integra and material of the unavailable name strialiventris referred here: Bolton, 1974c: 330; of conjugata: Villet, McKitterick & Robertson, 1999: 282..
 * major. Plectroctena caffra r. major Forel, 1894b: 74 (ergatoid q., not w.) MOZAMBIQUE. Arnold, 1915: 86 (w.). Subspecies of mandibularis: Emery, 1911d: 95; Santschi, 1914b: 54. Junior synonym of mandibularis: Emery, 1899e: 469; Bolton, 1974c: 330.
 * conjugata. Plectroctena minor st. conjugata Santschi, 1914e: 8 (w.q.) SOUTH AFRICA. Santschi, 1924a: 166 (m.); Wheeler, G.C. & Wheeler, J. 1989b: 52 (l.). Raised to species: Santschi, 1924a: 166. Junior synonym of mandibularis: Arnold, 1926: 209. Revived from synonymy: Bolton, 1974c: 326. Junior synonym of mandibularis: Villet, McKitterick & Robertson, 1999: 282.
 * integra. Plectroctena mandibularis var. integra Santschi, 1924a: 161 (w.m.) KENYA. Junior synonym of mandibularis: Bolton, 1974c: 330.

Plectroctena mandibularis

One syntype queen (ergatoid) and one syntype male in. Labelled “Port Natal. 58/13.” Acc. Reg.: “ 1858 no. 13. Port Natal. Purchased of Stevens. Collected by Gueinzius.”

In the original description Smith initially refers to the specimens as worker and male. He states, “worker not known” but goes on to say that the two were taken “in coitu.” The two specimens are certainly a male and an ergatoid queen. They were originally mounted on a single pin, the male above the ergatoid. The male has been remounted, separately.