Polyrhachis brevinoda

A rainforest species that builds silk nests between leaves in the lower arboreal zone.

Identification
Similar to Polyrhachis semiinermis from the Philippines and Polyrhachis danum from Sabah, Borneo. All three species have widely rounded pronotal shoulders and virtually parallel-sided petioles with greatly reduced or rudimentary spines. Polyrhachis brevinoda differs in having the propodeal declivity descending in an oblique curve while in P. semiinermis and P. danum the declivity is virtually vertical. Although the petiolar spines in P. brevinoda are short, the dorsal spines are relatively well defined, while the dorsal spines are more-or-less obsolete in the other two species. Polyrhachis brevinoda is also distinctly smaller than P. danum (HL 1.31-1.53 versus 1.65-1.87 respectively) and has dark brown to black legs (always distinctly red in P. danum).

Distribution
Kohout (2006): Main distribution centered on the Wet Tropics region of north Queensland, extending to Cape York Peninsula and to the southern parts of Papua New Guinea. A single specimen has also been collected in the West Kimberly District of north-western Australia.

This taxon was described from Australia.

Abundance
Common within the wet tropics of north Queensland

Castes
Males and immature stages (eggs, larvae and pupae) from the type colonies are deposited in the spirit collection (Kohout 2006)

Worker
Dimensions (holotype cited first): TL c. 5.49, 4.89-6.05; HL 1.40, 1.31-1.53; HW 1.31, 1.18-1.43; CI 93, 87-94; SL 1.81, 1.65-1.93; SI 138, 131-148; PW 1.09, 0.97-1.15; MTL 2.15, 1.93-2.31 (31 measured).

Clypeus in profile rather flat; basal margin weakly impressed. Frontal triangle indistinct. Frontal carinae sinuate with only moderately raised margins; frontal furrow weakly indicated. Sides of head in front of eyes very weakly convex; behind eyes rounding into convex occipital margin. Eyes convex, in full face view breaking lateral cephalic outline. Ocelli lacking; relative positions indicated in some specimens by minute depressions in cephalic sculpturation. Pronotum in dorsal view with humeri widely rounded; greatest pronotal width at or near mid-length of segment. Mesosoma in profile with pronotum rather steeply rising towards weakly convex summit; promesonotal suture distinct; metanotal groove lacking, slight depression in mesosomal outline indicating its position; propodeal dorsum sloping into oblique declivity in open curve. Petiole in profile with anterior face almost straight, posterior face convex; in dorsal view petiole rather narrow, sides more-or-less parallel; petiolar spines very short, dorsal pair reduced to denticles and lateral pair usually merely angulate; subpetiolar process in lateral view acute anteriorly, angular with weakly concave margin posteriorly. Anterior face of first gastral segment lower than height of petiole, widely rounding onto dorsum of segment.

Mandibles very finely, longitudinally striate.Head, mesosoma and gaster very finely shagreened with sculptural intensity increasing laterally and becoming more reticulate over meso- and metapleurae and lateral portions of petiole. Scattered minute punctures in various densities present over all dorsal surfaces.

Several curved hairs along mandibular masticatory borders, numerous very short, appressed hairs arising from pits towards mandibular bases. Anterior clypeal margin usually with 2 long, anteriorly directed setae medially and several short setae along margin laterally. Semierect to erect, mostly paired hairs near anterior and basal clypeal margins and along frontal carinae, a pair of somewhat longer hairs on vertex. Single pair of long, but shorter than greatest diameter of eye, undulated hairs on summit of mesosoma. Medium length, semierect hairs lining posterior margins of gastral segments, their density increasing on venter of gaster. Very short, appressed hairs, arising from minute punctures and pits, distributed over most dorsal body surfaces.

Colour. Head, mesosoma, coxae, petiole and gaster mostly black. Antennae very dark reddish-brown with apical ends a shade lighter. Mandibular masticatory borders and legs medium reddish-brown with tarsi and proximal ends of tibiae darker.

Queen
Dimensions: TL c. 6.75; HL 1.61; HW 1.40; CI 87; SL 2.00; SI 143; PW 1.53; MTL 2.50 (1 measured). Apart from sexual characters, closely resembling worker except: pronotal humeri narrowly rounded; mesoscutum marginally wider than long with lateral margins distinctly converging anteriorly, forming narrowly rounded anterior margin; median line relatively short, bifurcate and slightly raised; parapsides weakly raised posteriorly; mesoscutum in profile with widely rounded anterior face and rather flat dorsum. Mesoscutellum very weakly convex, only marginally elevated above dorsal plane of mesosoma; metanotal groove distinct. Propodeal dorsum armed with distinct denticles; declivity short and steep. Sculpturation, pilosity and colour virtually identical to worker.

Type Material
Holotype (QMT99333), most paratypes from holotype nest, 7 paratypes and 1 paratype queen in ; 4 paratypes (2 from holotype nest) each in ANIC, BMNH and MCZC; 2 paratypes (from holotype nest) each in, , , , and.

Type Locality Information
HOLOTYPE: QUEENSLAND, Kirrama Ra, c. 9km W of Kennedy, 18°12’S, 145°42’E, c. 110m, 4.vi.1996, rainforest, ex nest between leaves, R.J. Kohout acc. 96.14 (worker). PARATYPES: data (and nest) as for holotype (59 workers); Mission Beach, c. 4km WbyS of, 17°53’S, 146°04’E, 29.ii.1996, lowland rf., ex nest between leaves, S.K.A. Robson #256 (13 workers, 1 dealate Queen).