Polyrhachis sexspinosa

Polyrhachis sexspinosa is a relatively common and widespread species reported from most of the New Guinean mainland and islands of eastern Indonesia, including several doubtful records from the southern Philippines (Kohout, 1989). In Australia it ranges from Lockerbie Scrub south to Rocky River, northeast of Coen. Polyrhachis sexspinosa is somewhat singular within the sexspinosa-group in that it builds pocket-like nests of silk, vegetation debris and bark fragments against the trunks of rainforest trees (see images below).

Identification
Kohout (2010) - Polyrhachis sexspinosa resembles Polyrhachis reclinata, with their main distinguishing characters given in remarks section under the latter species.

Distribution based on Regional Taxon Lists
Australasian Region: Australia, New Caledonia. Indo-Australian Region: Indonesia, New Guinea, Philippines.

Castes
Males and immature stages (eggs, larvae in various stages of development and pupae) in QM spirit collection.

Nomenclature

 *  sexspinosa. Formica sexspinosa Latreille, 1802c: 126, pl. 4, fig. 21 (w.) INDONESIA ("Indes orientales"). Mayr, 1867a: 42 (q.); Karavaiev, 1927e: 26 (m.). Combination in Polyrhachis: Smith, F. 1858b: 59; in P. (Myrmhopla): Viehmeyer, 1916a: 167. Senior synonym of argentata: Lepeletier de Saint-Fargeau, 1835: 219; of irritabilis: Roger, 1863b: 6; of sericea: Bolton, 1975c: 12; of barnardi: Kohout & Taylor, 1990: 519. See also: Kohout, 2010: 196.
 * argentata. Formica argentata Fabricius, 1804: 413 (w.) NEW CALEDONIA. Combination in Polyrhachis: Smith, F. 1858b: 73. Junior synonym of sexspinosa: Lepeletier, 1835: 219; Roger, 1863b: 6.
 * irritabilis. Polyrhachis irritabilis Smith, F. 1859a: 141 (q.) INDONESIA (Aru I.). Junior synonym of sexspinosa: Roger, 1863b: 6.
 * sericea. Polyrhachis (Myrmhopla) sexspinosa var. sericea Karavaiev, 1927e: 26, fig. 13 (w.q.m.) INDONESIA (Aru I.). [Also described as new by Karavaiev, 1928: 316.] Junior synonym of sexspinosa: Bolton, 1975c: 12.
 * barnardi. Polyrhachis (Myrmhopla) barnardi Clark, 1928a: 39, pl. 1, figs. 37, 38 (w.) AUSTRALIA. Clark, 1930c: 14 (q.). Junior synonym of sexspinosa: Kohout & Taylor, 1990: 519. See also: Bolton, 1975c: 6.

Worker
Kohout (2010) - TL c. 12.60-14.76; HL 3.12-3.58; HW 1.84-2.17; CI 57-62; SL 3.78-4.48; SI 195-216; PW 1.81-2.03; MTL 4.79-5.74 (27 measured).

Anterior clypeal margin arcuate, often with very shallow median emargination. Clypeus with median carina, virtually straight in profile, posteriorly curving into moderately impressed basal margin. Frontal carinae sinuate with acute, highly raised margins. Sides of head in front of eyes almost straight, weakly diverging towards mandibular bases; behind eyes sides strongly tapered into narrow occipital margin with strongly developed occipital lobes. Eyes strongly convex, in full face view clearly exceeding lateral cephalic outline. Ocelli lacking, positions indicated by distinctly raised cephalic sculpture. Pronotal dorsum convex in profile, distinctly higher than mesonotum; humeri armed with strong, acute, more-or-less horizontal, anterolaterally directed spines; promesonotal suture distinct. Mesopleural process a distinct, dentiform lobe. Mesonotum and propodeum weakly convex in profile. Propodeal spines relatively long, virtually straight, in lateral view usually vertical to main axis of body or inclined forwards, tips sometimes curved posteriorly or inwards. Dorsum of petiole with a pair of lateral, dorsoposteriorly directed, acute spines.

Mandibles with numerous piliferous pits. Clypeus and sides of head finely reticulate-punctate with intensity and density of sculpturation distinctly increasing posteriorly, vertex and occiput rather coarsely sculptured. Mesosomal dorsum rugose with intensity decreasing posteriorly with propodeal dorsum finely reticulate-punctate. Gaster very finely shagreened.

Mostly silvery or grey, erect or variously curved hairs of variable lengths and densities over the entire body and appendages, including antennal scapes. Longest hairs on mesosomal dorsum, clearly longer than greatest diameter of eye. Head and mesosoma with somewhat untidy, relatively long, mostly silvery, suberect pubescence that never completely hides underlying sculpturation; most dense and more appressed on dorsum of head and mesosoma, somewhat radiating on sides. Gastral pubescence ranging from diluted on venter to dense on dorsum, where it is arranged in characteristic midline pattern.

Body black; mandibles, except bases, apical antennal segments and legs, including coxae, mostly light to medium reddish-brown.

Queen
Kohout (2010) - TL c. 13.46-16.28; HL 3.17-3.78; HW 1.86-2.37; CI 57-63; SL 3.73-4.59; SI 189-211; PW 2.02-2.82; MTL 4.74-5.64 (11 measured).

Queen very similar to worker; apart from usual characters identifying full sexuality, including three ocelli, complete thoracic structure and wings differing mainly in configuration of spines; pronotal spines shorter, projecting more anteriorly, tips directed forwards; propodeal spines distinctly shorter, oblique to main axis of body, weakly curved posteriorly; petiolar spines straight, distinctly shorter than in worker; sculpturation, pilosity and colour pattern identical to worker.

Type Material
Kohout (2010) - Neotype worker (by present designation). Type locality: PAPUA NEW GUINEA, West Sepik Prov., Pes Mission, 12 km SW of Aitape, 03°11’S, 142°15’E, <50 m, rf., 3.viii.1984 (RJK acc. 84.207), (examined).

Polyrhachis sexspinosa was originally described from a queen collected in the ‘East Indies’. The holotype queen of this species should be lodged in the, but an extensive search by the author failed locate it there or in any collections examined and it is considered lost. I support the earlier decision of Kohout & Taylor (1990: 518-520) who recognised the specimens of a nest series from Papua New Guinea (see above) as the voucher specimens of P. sexspinosa by designating one of these workers as the neotype for this name (ANIC, QM). A worker specimen was designated as the neotype of Polyrhachis sexspinosa (Latreille) from this colony of 50+ workers, a dealate queen and several males collected from a pocket nest on the trunk of a rainforest tree. The neotype has been deposited in ANIC.



Polyrhachis irritabilis

Holotype worker in. Labelled “Aroo” (= Aru I., New Guinea) and with a Donisthorpe type-label.