Polyrhachis schenckii

Kohout (2013): Polyrhachis schenckii is rather common in suitable localities in open eucalypt forest and savannah woodland. It is a ground nesting species with nest entrances usually hidden under a stone, piece of wood or a tuft of grass.

Identification
A member of the schenckii species-group in the Polyrhachis subgenus Hagiomyrma. Kohout (2013): Polyrhachis schenckii is easily recognised by its small size, light-red or reddish brown colour and the strongly posteriorly converging lateral margins of the promesonotal dorsum. It is one of the most widely distributed Hagiomyrma species, ranging from Papua New Guinea south across the Torres Strait to northern Australia. Polyrhachis schenckii forms a number of variable populations. The pronotal humeri are very narrowly rounded or bluntly angular in Australian specimens, while they are distinctly angular in most specimens from Papua New Guinea. The antennal scapes of specimens from the Northern Territory are somewhat longer than those of other populations (SI 151-159 in specimens from the Northern Territory versus 138-149 in Queensland and PNG specimens). Also, the posterior face of the petiolar node is rather evenly convex in specimens from New Guinea and Cape York Peninsula, while in specimens from north Queensland and the Northern Territory the posterior face is uneven, with the base somewhat broader and swollen in lateral view. However, when specimens across the whole distribution are compared, no other significant differences are evident and I consider them to represent a single, albeit variable, species.

Distribution
Kohout (1988) - Papua New Guinea across the Torres Strait islands to Australia, where it occurs on Cape York Peninsula, and in the Northern Territory.

Distribution based on Regional Taxon Lists
Australasian Region: Australia. Indo-Australian Region: New Guinea.

Castes
Males and immature stages in ANIC spirit collection.

Nomenclature

 *  schenckii. Polyrhachis schenkii Forel, 1886f: 198 (w.) NEW GUINEA.
 * [Justified emendation of spelling to schenckii: Dalla Torre, 1893: 268.]
 * Wheeler, G.C. & Wheeler, J. 1968: 221 (l.); Kohout, 2013e: 565 (q.).
 * Combination in P. (Hedomyrma): Santschi, 1920a: 569;
 * Combination in P. (Hagiomyrma): Emery, 1925b: 185.
 * Status as species: Dalla Torre, 1893: 268; Emery, 1911c: 250; Emery, 1925b: 185; Chapman & Capco, 1951: 267; Taylor & Brown, 1985: 140; Bolton, 1995b: 356; Dorow, 1995: 26; Kohout, 2000: 198 Kohout, 2013e: 563 (redescription).

Worker
Kohout (2013) - (syntype cited first): TL c. 5.2, 4.99-6.50; HL 1.45, 1.31-1.56; HW 1.15, 0.97-1.20; CI 79, 74-79; SL 1.55, 1.43-1.78; SI 135, 135-159; PW 1.00, 0.81-1.06; MW 0.40- 0.47; PMI 210-250; MTL 1.65, 1.53-2.00 (1+36 measured).

Anterior clypeal margin with emarginate, irregularly denticulate, median flange, flanked by acute angles. Clypeus with distinct median carina; sinuate in profile. Frontal triangle poorly indicated. Frontal carinae sinuate with weakly raised margins; central area rather flat with weakly impressed frontal furrow. Sides of head in front of eyes converging towards mandibular bases in almost straight line; behind eyes, sides rounding into convex occipital margin. Eyes relatively large, convex, in full face view clearly exceeding lateral cephalic outline. Ocelli lacking. Pronotal humeri narrowly rounded or bluntly angular (distinctly angular in some PNG specimens). Lateral margins of promesonotal dorsum with very narrowly raised margins, strongly converging posteriorly. Metanotal groove weakly impressed. Propodeal dorsum with lateral margins terminating in horizontal, divergent, acute spines. Petiole with posterior face sloping in even, moderately convex line; dorsum armed with horizontal, widely divergent, acute spines. Anterior face of first gastral segment higher than full height of petiole, evenly rounding onto dorsum.

Mandibles very finely, longitudinally striate with piliferous pits. Head, mesosoma and petiole distinctly reticulate-punctate; spines smooth and polished. Gaster shagreened.

Mandibular masticatory and outer borders with numerous, yellowish or golden, curved hairs. Anterior clypeal margin with a few longer setae medially and short setae fringing margin laterally. Numerous, mostly short, erect hairs on all body surfaces, including antennal scapes and outline of head in full face view; rather longer, somewhat posteriorly directed hairs on gaster. Rather diluted, closely appressed, golden pubescence over most body surfaces; pubescence usually more abundant, somewhat longer and mostly pale golden or silvery on dorsum of gaster, but almost lacking in some specimens.

Yellowish- to rusty-red, with distinctly darker patches variously on vertex of head, dorsum of mesosoma and petiole. Mandibles with teeth dark reddish-brown; spines light reddish-brown. Anterior clypeal margin, frontal carinae and lateral margins of mesosoma narrowly lined with dark brown or black. Appendages, including coxae, light to medium reddish-brown; tarsi a shade darker. Gaster mostly dark, reddish-brown.

Queen
Kohout (2013) - TL c. 6.85-7.16; HL 1.56-1.59; HW 1.18-1.22; CI 74-78; SL 1.56-1.59; SI 128-135; PW 1.40-1.47; MTL 1.81-1.84 (6 measured).

Apart from sexual characters, very similar to worker except: pronotal humeri narrowly rounded or bluntly angular in some specimens; mesoscutum as wide as long, lateral margins converging anteriorly into moderately rounded anterior margin; median line weakly indicated; parapsides flat; mesoscutum in profile widely rounded onto flat dorsum. Mesoscutellum flat, only marginally raised above dorsal plane of mesosoma. Propodeum armed with pair of horizontal, acute spines; dorsum rounding medially into virtually vertical declivity. Petiole with posterior face weakly convex; spines rather short, widely divergent. Sculpturation, pilosity, pubescence and colour identical to worker.

References based on Global Ant Biodiversity Informatics

 * Andersen A. N. 1993. Ants as indicators of restoration success at a uranium mine in tropical Australia. Restoration Ecology 1(3): 156-167.
 * Andersen A. N., B. D. Hoffmann, and S. Oberprieler. 2016. Diversity and biogeography of a species-rich ant fauna of the Australian seasonal tropics. Insect Science DOI 10.1111/1744-7917.12402
 * Andersen A. N., J. C. Z. Woinarski, and B. Hoffman. 2004. Biogeography of the ant fauna of the Tiwi Islands, in northern Australia's moonsoonal tropics. Australian Journal of Zoology 52: 97-110.
 * Andersen A. N., M. Houadria, M. Berman, and M. van der Geest. Rainforest ants of the Tiwi Islands: a remarkable centr of endemism in Australia's monsoonal tropics. Insectes Sociaux 59: 433-441.
 * Andersen A. N., R. R. Ribbons, M. Pettit, and C. L. Parr. 2014. Burning for biodiversity: highly resilient ant communities respond only to strongly contrasting fire regimes in Australias seasonal tropics. Journal of Applied Ecology 51: 14061413.
 * Andersen A. N., T. Hertog, and J. C. Z. Woinarski. 2006. Long-term fire exclusion and ant community structure in an Australian tropical savanna: congruence with vegetation succession. Journal of Biogeography 33: 823-832.
 * Andersen, Alan N., John C.Z. Woinarski and Ben D. Hoffman. 2004. Biogeography of the ant fauna of the Tiwi Islands, in northern Australia's monsoonal tropics. Australian Journal of Zoology 52: 97-110.
 * Emery C. 1911. Formicidae. Résultats de l'expédition scientifique néerlandaise à la Nouvelle-Guinée en 1907 et 1909 sous les auspices de Dr. H. A. Lorentz. Nova Guin. 9: 249-259
 * Forel A. 1886. Études myrmécologiques en 1886. Annales de la Société Entomologique de Belgique. 30: 131-215.
 * Janda M., G. D. Alpert, M. L. Borowiec, E. P. Economo, P. Klimes, E. Sarnat, and S. O. Shattuck. 2011. Cheklist of ants described and recorded from New Guinea and associated islands. Available on http://www.newguineants.org/. Accessed on 24th Feb. 2011.
 * Kohout R. J. 2000. A review of the distribution of the Polyrhachis and Echinopla ants of the Queensland wet tropics (Hymenoptera: Formicidae: Formicinae). Memoirs of the Queensland Museum 46: 183-209
 * Kohout R.J. 2013. Revision of Polyrhachis (Hagiomyrma) Wheeler, 1911 (Insecta: Hymenoptera: Formicidae: Formicinae). Memoirs of the Queensland Museum  Nature 56: 487577
 * Reichel H., and A. N. Andersen. 1996. The rainforest ant fauna of Australia's Northern Territory. Australian Journal of Zoology 44: 81-95.
 * Robson Simon Ant Collection, 05-Sept-2014
 * Robson Simon Database Polyrhachis -05 Sept 2014
 * 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.
 * Taylor R. W., and D. R. Brown. 1985. Formicoidea. Zoological Catalogue of Australia 2: 1-149.
 * Viehmeyer H. 1912. Ameisen aus Deutsch Neuguinea gesammelt von Dr. O. Schlaginhaufen. Nebst einem Verzeichnisse der papuanischen Arten. Abhandlungen und Berichte des Königlichen Zoologischen und Anthropologische-Ethnographischen Museums zu Dresden 14: 1-26.
 * Woinarski J.C.Z., H. Reichel, and A.N. Andersen. 1998. The distribution of ants on the Wessel and English Company islands, in the seasonal tropics of Australia's Northern Territory. Australian Journal of Zoology 46: 557-578.