Polyrhachis bicolor

Polyrhachis bicolor is a relatively common species at suitable localities around Darwin, where it builds nests of silk and vegetation debris among the leaves of trees and shrubs notably along the margins of monsoon rainforests. In spite of being a rather common species in mangroves and lowland forests along the Gulf of Papua, it has not yet been recorded from Cape York Peninsula or elsewhere in north Queensland. (Kohout 2010)

Identification
A member of the Polyrhachis bicolor species group.

Kohout (2008) - Across its large range, P. bicolor, as currently interpreted, consists of a large number of overlapping populations that differ to varying extents from the holotype from Burma (= Myanmar). About eleven infraspecific forms are presently associated with P. bicolor, many clearly representing valid species. In addition, at least twice as many closely related new species are presently in collections awaiting description.

Kohout (2010) - After examination of a large amount of material from across the entire range I consider the Australian population to represent the nominal form.

The two bicolor-group species known from Sulawesi are distinguished as follows:


 * Distinctly bicoloured; head, mesosoma and petiole black with mandibles, antennae, legs, including coxae and gaster orange or light reddish-brow . . . . . Polyrhachis bicolor


 * Unicoloured; body black with only mandibles rusty-red and tibiae dark reddish-brown (in copal) . . . . . Polyrhachis subfossa

Distribution
Kohout (2008) - A widespread and relatively common species, extending from South East Asia south to Indonesia, New Guinea and Northern Australia.

Distribution based on Regional Taxon Lists
Australasian Region: Australia. Indo-Australian Region: Borneo, Brunei Darussalam, Indonesia, Krakatau Islands, Malaysia, New Guinea, Philippines, Singapore. Oriental Region: Bangladesh, Cambodia, India, Laos, Myanmar, Thailand, Vietnam. Palaearctic Region: China.

Castes
Males and immature stages (eggs, larvae and pupae) deposited in the QM spirit collection.

Nomenclature

 *  bicolor. Polyrhachis bicolor Smith, F. 1858b: 65 (q.) MYANMAR. Mayr, 1862: 681 (w.). Combination in P. (Myrmhopla): Viehmeyer, 1916a: 167. Senior synonym of concolor: Kohout, 1998: 515. See also: Kohout, 2010: 173. Current subspecies: nominal plus atrocastanea, aurata, aurinasis, brachyacantha, comata, erecta, exflavicornis, fumata, weyeri.
 * concolor. Polyrhachis bicolor var. concolor Forel, 1910d: 129 (w.q.m.) PHILIPPINES. Combination in P. (Myrmhopla): Emery, 1925b: 194. Junior synonym of bicolor: Kohout, 1998: 515.

Worker
Kohout (2010) - TL c. 6.00-7.06; HL 1.43-1.68; HW 1.12-1.31; CI 77-79; SL 1.96-2.34; SI 172-182; PW 0.87-1.03; MTL 2.34-2.68 (10 measured)

Mandibles with 5 teeth, progressively reducing in length towards base. Anterior clypeal margin with shallow median flange, laterally flanked by acute angles. Clypeus with poorly defined, posteriorly weakly elevated, median carina; clypeus virtually straight 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 virtually straight line; behind eyes sides rounding into convex occipital margin. Eyes strongly convex, in full face view clearly breaking lateral cephalic outline. Ocelli indistinct. Mesosoma laterally immarginate. Pronotal dorsum weakly convex in profile; humeri armed with slender, relatively long, acute, anterolaterally directed spines with tips slightly turned upwards. Promesonotal suture distinct; mesonotum straight in profile with metanotal groove marked by slight step in outline. Propodeal dorsum rather short with a pair of slender, obliquely elevated, subparallel, acute spines. Petiole nodiform with medially weakly elevated dorsum and pair of relatively long and slender, laterally and posteriorly curved, acute spines. Anterior face of first gastral tergite rounding in evenly convex line onto dorsum of segment.

Mandibles smooth and polished with shallow piliferous pits. Head, mesosoma and gaster closely reticulate-punctate with sculpture almost completely hidden by overlying pubescence. Spines weakly rugose at bases, smooth and polished towards tips. Gaster finelly shagreened.

Mandibular masticatory borders with 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 mostly posteriorly directed. Very distinct, relatively long, silvery pubescence almost completely hiding underlying sculpturation on head, mesosoma and petiole, except spines. Gastral pubescence more appressed and somewhat diluted, not obscuring fine sculpturation.

Head, mesosoma and petiole black; mandibles, median portion of anterior clypeal margin, antennae, legs, coxae, tips of spines, subpetiolar process and gaster, orange or light reddish-brown.

Queen
Kohout (2010) - TL c. 8.97; HL 1.87; HW 1.40; CI 75; SL 2.62; SI 187; PW 1.78; MTL 3.06 (1 measured).

Very similar to worker and apart from sexual characters, including three ocelli, fully developed mesosoma and wings, differing as follows: Pronotal spines reduced to more-or-less triangular, acute teeth, barely longer than basal widths. Mesoscutum with anterior margin widely and evenly rounded in dorsal view; median line bifurcate anteriorly; parapsides rather flat anteriorly, raised posteriorly. Mesoscutellum weakly convex, slightly elevated above dorsal plane of mesosoma; metanotal groove distinct. Propodeal spines very short, obliquely elevated, somewhat dorsoventrally flattened, tips rounded. Petiolar spines similar to those in worker but stronger at base and distinctly shorter; dorsum of petiole with rather distinct, blunt intercalary tooth.