Polyrhachis nigripes

In Australia, P. nigripes has been recorded only once from Iron Range National Park on Cape York Peninsula where a nest of silk and vegetation debris was collected on the ground in monsoon rainforest along the Claudie River. The twig and leaves upon which the nest was built were completely dry and had apparently fallen very recently from its original position higher on the tree. It contained a dealate queen, 19 workers and brood (many eggs and larvae). (Kohout 2010)

Identification
A member of the Polyrhachis bicolor species group.

Kohout (2010) - Polyrhachis bicolor and P. nigripes are certainly very closely related. The main differences separating them are their colour patterns which appear to be constant in all material examined. Another key difference is the profile of the mesosoma which features a virtually flat mesonotum in P. bicolor, while in P. nigripes the pronotal and mesonotal dorsa form a weak, but evenly convex line. In addition, P. bicolor has distinctly more slender spines, notably those on the propodeum, which, although they are closer together, are clearly separated at their bases and are parallel for their full length. In contrast the spines in P. nigripes are distinctly stronger, with the inner bases of the propodeal spines somewhat continuous across the propodeal dorsum, forming a medially incomplete “U” shape in dorsal view. The propodeal spines are also slightly divergent and weakly curved along their length. New Guinean and Australian specimens of P. nigripes are very similar in appearance.

Distribution
Kohout (2010) - The distribution of P. nigripes in New Guinea appears to be concentrated mainly along the coast of the Gulf of Papua, with only a few doubtful records from Irian Jaya and the north of the island. In Australia, P. nigripes has been recorded only once from Iron Range National Park on Cape York Peninsula.

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

Castes
Males unknown. Immature stages (eggs and larvae) deposited in the QM spirit collection.

Nomenclature

 *  nigripes. Polyrhachis bicolor var. nigripes Emery, 1897d: 592 (w.) NEW GUINEA. Combination in P. (Myrmhopla): Emery, 1925b: 194. Raised to species: Kohout, 2010: 176.

Worker
Kohout (2010) - TL c. 5.74-6.25; HL 1.40-1.59; HW 1.15-1.31; CI 79-82; SL 1.87-2.06; SI 157-169; PW 0.87-1.03; MTL 2.18-2.46 (4 measured).

Mandibles with 5 teeth. Anterior clypeal margin with shallow, median flange, laterally flanked by rather acute teeth. Clypeus with poorly defined, posteriorly elevated median carina, weakly convex in profile with rather shallow basal margin. Frontal carinae sinuate with well raised margins; frontal furrow indistinct. Sides of head in front of eyes converging anteriorly towards mandibular bases in straight line; behind eyes sides rounding into convex occipital margin. Eyes strongly convex, relatively large, in full face view clearly breaking lateral occipital margin. Ocelli indistinct. Mesosoma laterally immarginate. Pronotal and mesonotal dorsa forming even, weakly convex line in profile; pronotal humeri armed with fine, slender, relatively long, acute, anterolaterally directed spines, tips slightly turned downwards. Promesonotal suture distinct; metanotal groove feebly marked by rather flat, bowed line. Propodeal dorsum rather short with a pair of obliquely elevated, fine, slender, subparallel, acute spines. Petiole nodiform, dorsum medially weakly elevated, armed with a pair of relatively long, slender, laterally and posteriorly curved, acute spines. Anterior face of first gastral segment widely rounding onto dorsum of segment.

Mandibles rather smooth or very finely, longitudinally striate with shallow piliferous pits. Head, mesosoma and gaster closely reticulate punctate with sculpture almost completely hidden by overlying pubescence. Spines weakly rugose, tips rather smooth and polished. Gaster finely shagreened.

Mandibular masticatory borders with a few curved, golden hairs. Anterior clypeal margin medially with several, medium length, anteriorly directed, golden setae. Head, including clypeus, mesosoma and gaster with numerous, mostly erect and variously curved, somewhat untidy, long silvery hairs, some longer than greatest diameter of eyes; hairs on gaster somewhat shorter and mostly posteriorly directed. Very distinct, relatively long, silvery pubescence almost completely hiding underlying sculpturation on head, mesosoma and petiole, except apical portions of spines. Gastral pubescence more appressed and diluted, not obscuring fine sculpturation.

Head, including anterior clypeal margin, antennal scapes, mesosoma, including fore coxae, spines, and petiole, including subpetiolar process, black; legs, including mid and hind coxae and basal antennal segments dark to very dark reddish-brown or black; mandibles, apical antennal segments and gaster orange or light reddish-brown. Dorsum of first gastral tergite with darker, irregular, somewhat diffused, reddish-brown patch medially.

Queen
Kohout (2010) - TL c. 8.52; HL 1.84; HW 1.50; CI 81; SL 2.34; SI 156; PW 1.75; MTL 3.81 (1 measured)

Essentially like worker and apart from sexual characters, including three ocelli and complete thoracic structure, differing as follows: pronotal spines distinctly reduced in length, about twice as long as their basal widths. Mesoscutum with anterior margin evenly rounded in dorsal view; median line bifurcate anteriorly and dorsally; parapsides weakly raised posteriorly. Mesoscutellum slightly elevated above dorsal plane of mesosoma; metanotal groove distinct. Propodeal spines short, obliquely elevated, their inner margins continued inwards but not meeting medially. Petiolar spines similar to those in worker but stronger and distinctly shorter; dorsum of petiole bluntly raised medially. Sculpturation, pilosity and colour virtually identical to worker.

Type Material
Kohout (2010) - Holotype worker. Type locality: NEW GUINEA: Paumomu River (= Angabanga R.) (L. Loria),.