Polyrhachis brutella

Polyrhachis brutella inhabits open eucalypt forests, seemingly preferring rocky ground in which to build their nests. Two of the nests dug up at the type locality had their tunnels excavated along and under large boulders with the lowest chambers reaching a depth of about 50-70cm.

Identification
A member of the ammon species-group in the Polyrhachis subgenus Hagiomyrma. Polyrhachis brutella is similar to Polyrhachis brisbanensis but is generally larger (HL 2.28-2.56 in P. brutella versus HL 2.15-2.37 in P. brisbanensis), with most of the distinguishing characters given in the remarks section under the latter. Other characters specific to P. brutella include the lack of a light band at the bases of mandibular teeth, the blunt lateral angles of the anterior flange of the clypeus, the subparallel, undilated lateral margins of the pronotal dorsum, the distinctly sinuate petiolar spines with their tips bent outwards, the distinctly shorter pilosity and the very short, rather diluted body pubescence, notably on the pronotal and mesonotal dorsa. The gastral pubescence in both species is pale gold or silvery, with an almost identical median patch on first gastral tergite.

The distribution of P. brutella extends from Eungella National Park south to Rockhampton and as far west as Canarvon National Park, with an apparently isolated population at Turtle Rock in the Hervey Range near Townsville. Specimens from the latter population closely resemble those from Mt Archer, except in having marginally shorter antennal scapes (SI 156-164 in specimens from Turtle Rock versus 167-181 in other specimens) and a wider petiolar dorsum with divergent petiolar spines that have their base more widely separated.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Castes
Males and immature stages (eggs, larvae and pupae from holotype colony) present in the QM collection.

Nomenclature

 *  brutella. Polyrhachis (Hagiomyrma) brutella Kohout, 2013: 509, figs. 2C-D (w.q.) AUSTRALIA.

Worker
Dimensions (holotype cited first): TL c. 10.89, 10.28-11.54; HL 2.50, 2.28-2.62; HW 2.02, 1.84-2.12; CI 81, 78-82; SL 3.43, 3.12-3.53; SI 170, 155-181; PW 1.72, 1.53- 1.72; MW 1.25, 1.15-1.31; PMI 138, 125-142; MTL 4.03, 3.88-4.28 (26 measured).

Anterior clypeal margin with median flange, laterally flanked by blunt angles. Clypeus with distinct longitudinal carina, sinuate in profile, posteriorly narrowly rounding into weakly impressed basal margin. Frontal carinae sinuate with moderately raised margins. Sides of head in front of eyes converging towards mandibular bases in virtually straight line; behind eyes, sides abruptly rounding into only moderately convex occipital margin. Eyes convex, clearly breaking lateral cephalic outline in full face view. Ocelli lacking. Pronotal dorsum almost quadrate, only marginally wider than long, lateral margins more-or-less parallel, usually narrowly emarginated or notched at midlength; humeri rounded with raised margins, weakly concave dorsally. Mesonotal margins weakly raised, converging into weakly indicated, posteriorly bowed metanotal groove. Propodeal dorsum relatively short, rounding into steep, convex declivity; lateral margins terminating in long, slender spines, with tips bent outwards. Petiolar spines sinuate, subparallel or even weakly posteriorly converging, with tips bent weakly outwards and upwards.

Mandibles longitudinally striate with numerous piliferous pits. Head and mesosoma finely reticulate-punctate, with sculpturation irregularly longitudinal along frontal carinae and on vertex; more coarsely sculptured on sides of head. Gaster finely shagreened.

Mandibles with numerous curved, golden hairs at masticatory borders and along outer borders. Anterior clypeal margin with only a few, anteriorly directed setae medially and very short setae laterally. Several pairs of medium length, golden hairs on clypeus, along frontal carinae and on vertex. Numerous, relatively long hairs on dorsum of mesosoma and petiole, fore coxae and along ventral surfaces of femora. Gaster with numerous, posteriorly inclined, medium length, golden hairs. Closely appressed, mostly silvery pubescence in various densities over most body surfaces, with somewhat pale golden hue along median line of mesosoma; first gastral tergite with distinct, reddish-brown coloured, median patch of pubescence, diffused laterally into rich golden pubescence that blends into silvery on sides and venter of gaster.

Black, with only mandibles dark reddish-brown.

Queen
Dimensions: TL c. 10.84-12.25; HL 2.25; HW 1.72; CI 76; SL 2.92-3.03; SI 170-176; PW 2.59- 2.84; MTL 3.73-3.88 (2 measured).

Apart from sexual characters and larger size, similar to worker, except: longitudinal clypeal carina indistinct; sides of head in front of eyes subparallel, very weakly concave; eyes distinctly more convex, virtually protuberant. Pronotal humeri subangular; mesoscutum rather massive, as long as wide with anterior margin widely rounded; median line distinctly bifurcate; dorsum flat with parapsides only weakly raised posteriorly. Mesoscutellum with dorsum convex, distinctly raised above dorsal plane of mesosoma. Propodeum with spines weakly divergent, shorter than in worker; dorsum rounding evenly into virtually vertical declivity. Petiole armed with very short, posteriorly and weakly inwardly curved spines. Sculpturation, pilosity, pubescence and colour identical to that in worker, except virtual lack of pilosity and pubescence on dorsum of mesoscutum.

Etymology
Derived from the Latin word brutus, meaning rough, in reference to the harsh conditions under which the nest of the type series was excavated from stony ground.

Determination Clarifications
The Turtle Rock population of P. brutella was listed earlier as ‘Hagio 16’ by Kohout, 2000: 200).

References based on Global Ant Biodiversity Informatics

 * Kohout R.J. 2013. Revision of Polyrhachis (Hagiomyrma) Wheeler, 1911 (Insecta: Hymenoptera: Formicidae: Formicinae). Memoirs of the Queensland Museum  Nature 56: 487577