Polyrhachis semiaurata

Polyrhachis semiaurata ranges from Blackdown Tableland in central Queensland, south to northern Victoria and as far west as Carnarvon National Park in central Queensland. In its nesting habits, P. semiaurata is both lignicolous and terrestrial, with some colonies found nesting in the partly burned trunks of felled trees.

Identification
A member of the ammon species-group in the Polyrhachis subgenus Hagiomyrma. With its rich golden pubescence on the head and mesosoma, combined with a black, polished and virtually pubescence free gaster, Polyrhachis semiaurata is one of the most easily recognisable species.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Castes
Males and immature stages present in the QM collection.

Nomenclature

 *  semiaurata. Polyrhachis semiaurata Mayr, 1876: 71 (w.) AUSTRALIA. Kohout, 2013: 522 (q.). Combination in P. (Hagiomyrma): Forel, 1915b: 108.

Worker
Kohout (2013) - (syntypes cited first): TL c. 9.47-9.63, 9.02-10.38; HL 2.34- 2.40, 2.21-2.43; HW 1.84-1.93, 1.72-1.96; CI 79- 80, 78-84; SL 2.81-2.87, 2.62-2.92; SI 149-153, 144-153; PW 1.61-1.65, 1.50-1.65; MW 1.13-1.18, 1.13-1.25; PMI 140-142, 131-142; MTL 3.63-3.68, 3.38-3.68 (2+16 measured).

Anterior clypeal margin with obtusely denticulate, median flange, laterally flanked by blunt angles. Clypeus with median carina, straight or very weakly sinuate in profile, rounding posteriorly into well impressed basal margin. Frontal carinae with moderately raised margins. Sides of head in front of eyes converging towards mandibular bases in almost straight line; behind eyes, sides rounding into convex occipital margin. Eyes convex, in full face view clearly exceding lateral cephalic outline. Ocelli lacking. Pronotal dorsum with humeri rounded; lateral margins emarginate or notched at about midlength, widely rounding into well impressed promesonotal suture. Mesononal dorsum with lateral margins weakly raised towards medially flat, metanotal groove. Propodeal dorsum armed with horizontal, divergent spines, distinctly curved outwards from midlength. Petiole in lateral view with anterior face rounded into elevated, sinuate spines, with tips curved upwards; dorsum concave medially, spines only weakly divergent in dorsal view. Anterior face of first gastral tergite widely rounding onto dorsum.

Mandibles finely, irregularly, striate-rugose with piliferous pits. Head, mesosoma and gaster reticulate-punctate; basal half of propodeal spines sculptured, smooth and polished towards tips; petiolar spines smooth and polished along full length. Gaster finely shagreened, smooth and rather polished.

Mandibular masticatory and outer borders with curved, golden hairs. Anterior clypeal margin with a few longer, golden setae medially and fringe of shorter setae laterally. Head, mesosoma, petiole and gaster with abundant, golden, erect and/or variously curved, hairs, distinctly longer than greatest diameter of eyes, except: clypeus with only a few paired, long hairs along anterior and basal borders; leading edge of antennal scapes with fringe of short, semierect, bristle-like hairs; head in full face view with a few shorter hairs between occipital corners and mandibular bases; hairs on gaster more posteriorly inclined. Abundant, rather long, rich golden, appressed pubescence on most body surfaces, except clypeus, appendages and gaster; pubescence denser and distinctly medially radiating on dorsum of mesosoma, completely hiding underlying sculpturation. Very diluted, pale golden or silvery pubescence on gaster, lacking in some specimens.

Black throughout, only mandibles reddish-brown.

Queen
Kohout (2013) - TL c. 9.17-9.42; HL 1.96- 2.06; HW 1.59-1.65; CI 80-81; SL 2.42-2.50; SI 151-153; PW 1.86-1.96; MTL 2.96-3.06 (3 measured).

Apart from sexual characters and generally smaller size (HL 1.96-2.06 in queen, versus 2.21- 2.43 in worker), very similar to worker, except: mesoscutum with dorsum flat, as wide as long; median line bifurcate; parapsides flat, only marginally raised posteriorly. Mesoscutellum very weakly convex, not elevated above dorsal plane of mesosoma. Propodeal spines very slender, divergent; petiolar spines similar to those in worker, but shorter. Pilosity generally much shorter and less dense on head and dorsum of mesosoma, head in full face view without fringing hairs between eyes and mandibular bases. Pubescence similar to worker, except for dorsum of mesoscutum where it is rather diluted, with only a patch of closely appressed hairs along midline. Sculpturation and colour virtually identical to worker.

References based on Global Ant Biodiversity Informatics

 * Forel A. 1915. Results of Dr. E. Mjöbergs Swedish Scientific Expeditions to Australia 1910-13. 2. Ameisen. Ark. Zool. 9(16): 1-119
 * Kohout R.J. 2013. Revision of Polyrhachis (Hagiomyrma) Wheeler, 1911 (Insecta: Hymenoptera: Formicidae: Formicinae). Memoirs of the Queensland Museum  Nature 56: 487577
 * Taylor R. W. 1987. A checklist of the ants of Australia, New Caledonia and New Zealand (Hymenoptera: Formicidae). CSIRO (Commonwealth Scientific and Industrial Research Organization) Division of Entomology Report 41: 1-92.