Polyrhachis glabrinotum

Polyrhachis glabrinota is a predominantly arboreal species that builds nests between leaves in the lower arboreal zone. However, several colonies were located nesting in bamboo internodes. In contrast, the nests of the closely allied, possibly polydomous, New Guinean Polyrhachis bubastes were collected from the crown of a recently felled rainforest tree. (Kohout 2010)

Identification
A member of the Polyrhachis sexspinosa species group.

Kohout (2010) - With its smaller size, rather smooth and polished pronotal dorsum and short, sparse pubescence, P. glabrinota is easily distinguished from all other Australian members of the group. However, it closely resembles Polyrhachis bubastes from New Guinea, with both species similar in size, general body form and shape of the petiole. They differ in the intensity of the pronotal sculpturation that, in P. glabrinota, is only weakly sculptured, rather smooth and polished, while it is very coarsely sculptured in P. bubastes. The body in P. glabrinota is also generally bicoloured with the parts of mesosoma and petiole more-or-less reddish-brown, while the body in P. bubastes is mostly uniformly black.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Castes
Males and immature stages (eggs, larvae in various stages of development and pupae) in QM spirit collection.

Nomenclature

 *  glabrinotum. Polyrhachis (Myrmhopla) glabrinotum Clark, 1930c: 13, fig. 1 (w.) AUSTRALIA. Kohout, 2010: 188 (q.). See also: Bolton, 1975c: 8.

Kohout (2010) - Recent examination of a considerable amount of sexspinosa-group material from eastern Indonesia and New Guinea has revealed a number of specimens closely comparable to P. glabrinota. Like that species, they have smooth pronotal dorsums and are bicoloured, but more distinctly than most of the recently collected Australian specimens. The reddish-brown colour of the specimens from Australia is somewhat darker and more-or-less restricted to the propodeum, petiole and appendages, while the specimens from the Aru Islands and New Guinean mainland are distinctly bicoloured with the head black and all of the mesosoma, petiole and appendages light to medium reddish-brown. These specimens also bear a rather prominent, median, longitudinal depression on the pronotal dorsum, which is only shallowly indicated in some of the Australian specimens. Specimens from Wammar, Aru Is (V. Karavaiev #2595, IZAS) were misidentified as Polyrhachis rugifrons Fr. Smith (Karavaiev, 1927: 25), while a series from Wanuma, Madang District (N. L. H. Kraus, BPBM) were furnished with an identification tag of unknown origin inscribed ‘cf. bubastes new’. In addition, two nest series of closely comparable specimens, complete with sexuals, were more recently collected at Lumi, Torricelli Mts (RJK accs 84.271, 283). Specimens of all these populations vary in several characters, including the direction and length of the propodeal spines and the relative height of the petiole, but overall the specimens are very similar. However, when directly compared with P. glabrinota, these specimens appear rather distinct and in spite of some similarity I am hesitant to consider them conspecific. Like Bolton (1975), I consider P. glabrinota to be an Australian endemic and believe that the Indonesian and New Guinean material belong to a closely allied, but separate biological species.

Worker
Kohout (2010) - (syntypes cited first) TL c. 10.18-11.00, 9.78-11.95; HL 2.50-2.64, 2.46-2.96; HW 1.62-1.69, 1.53-1.93; CI 63-66, 59-66; SL 3.12-3.32, 2.93-3.35; SI 190-197, 181-197; PW 1.44-1.48, 1.40-1.78; MTL 3.73-3.88, 3.58-4.18 (22 measured).

Anterior clypeal margin arcuate, entire. Clypeus with blunt median carina, straight or weakly convex in profile, posteriorly rounding into well impressed basal margin. Frontal triangle distinct. Frontal carinae sinuate with only moderately raised margins; central area with median longitudinal carina. Sides of head in front of eyes weakly convex; behind eyes sides distinctly tapering into relatively narrow occipital margin with lateral lobes weakly developed, not visible with head in full face view. Eyes protuberant, in full face view exceeding lateral cephalic outline. Ocelli lacking. Pronotal dorsum convex in profile; summit with more-or-less distinct, shallow, longitudinal depression; humeri armed with strong, acute, more-or-less horizontal, anterolaterally curved spines; promesonotal suture distinct. Mesonotum virtually flat in profile; mesopleural process a well-developed lobe. Propodeal spines relatively long, obliquely elevated from their bases, curved and moderately divergent. Dorsum of petiole with a pair of laterally and weakly posteriorly directed, acute spines, with their tips turned slightly downwards.

Clypeus and sides of head in front of eyes finely reticulate-punctate, rather smooth and polished; density and intensity of sculpturation increasing posteriorly with central area, vertex and sides of head towards occipital margin deeply and coarsely sculptured. Pronotal dorsum rather smooth and polished or with shallow weak rugosity. Mesonotum, sides of mesosoma and petiole rugose with propodeal dorsum relatively smooth. Gaster very finely shagreened.

Numerous, mostly white or pale yellow, relatively short hairs, not exceeding greatest diameter of eye in length, present over entire body and appendages, including antennal scapes and spines. Rather diluted, white or grey, appressed or suberect pubescence developed in various densities over all body surfaces, more dense and closely appressed on clypeus, sides of head and fore coxae; somewhat suberect and variously radiating pubescence on sides of mesosoma. Gaster with mostly white, appressed pubescence arranged in characteristic midline pattern.

Generally bicoloured; head black, mesosoma black or dark reddish-brown with propodeum and petiole distinctly lighter. Colour variable; black in most recently collected specimens but distinctly lighter reddish-brown in some syntypes. Mandibular masticatory borders, tips of apical antennal segments, and legs, including coxae, light to medium reddish-brown.

Queen
Kohout (2010) - TL c. 11.34-13.10; HL 2.65-2.96; HW 1.62-1.81; CI 59-64; SL 3.17-3.53; SI 183-199; PW 1.90-2.21; MTL 3.93-4.33 (9 measured).

Apart from sexual characters, very similar to worker. Mesoscutum virtually as wide as long with lateral margins converging into narrowly rounded anterior margin; median line slightly raised; dorsum flat in profile with parapsides only weakly raised posteriorly. Mesoscutellum flat, marginally elevated above dorsal plane of mesosoma, posteriorly rounding into metanotal groove. Spines similar to worker but shorter with propodeal pair horizontal. Sculpturation, pilosity, pubescence and colour identical to worker.

Type Material
Kohout (2010) - Syntype workers: QUEENSLAND, Cape York (W. B. Barnard),, , , , (examined).



References based on Global Ant Biodiversity Informatics

 * Kohout R. J. 2010. A review of the Australian Polyrhachis ants of the subgenera Myrmhopla Forel and Hirtomyrma subgen. nov. (Hymenoptera: Formicidae: Formicinae). Memoirs of the Queensland Museum - Nature 55:167-204.