Nothing is known about the biology of Polyrhachis roberti.
Kohout (2007) - This species is characterized by well developed pronotal and propodeal teeth and notably by its remarkable petiole, which is strongly transverse and furnished with a pair of acute dorsal teeth with a medial emargination between them and relatively long, lateral spines. It stands near Polyrhachis simulans with both sharing similar sculpture of the head and mesosoma, including the absence of any striae on their mandibles and clypeus. However, they differ in a number of characters, of which the most distinct are discussed under simulans.
Keys including this Species
Distribution based on Regional Taxon Lists
Distribution based on AntMaps
Distribution based on AntWeb specimens
Check data from AntWeb
The subgenus this species is a member of, Aulacomyrma, is poorly colected. Kohout (2007) summarized what is known about their biology in a revision of the species in the subgenus. This offers an explanation as to why most Aulacomyrma are known from few collections and specimens. There are only two records of nests being found. A small colony of Polyrhachis dohrni was collected by Kohout from a dry hollow twig on a living tree at the edge of lowland rainforest. The internal walls of the twig cavity were lined with a little silk. Ward collected a nest of Polyrhachis wardi from a dry twig of a rainforest tree. The colonies of both species were rather small, with only a few workers (5 and 11 respectively, including 2 and 3 alate queens and a single male). If such a nesting pattern is the norm for other species of the subgenus, that might explain the general scarcity of Aulacomyrma material even in the best collections. Many Aulacomyrma species are described and only known from a holotype.
Known only from the worker caste.
The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.
- roberti. Polyrhachis (Aulacomyrma) roberti Kohout, 2007a: 206, figs. 28, 31, 34 (w.) NEW GUINEA.
Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.
TL c. 5.74-6.15 (6.15); HL 1.59-1.62 (1.62); HW 1.40-1.43 (1.43); CI 88-89 (88); SL 1.62-1.65 (1.65); SI 114-116 (115); PW 1.18-1.25 (1.25); MTL 1.56-1.65 (1.65) (3 measured).
Median portion of anterior clypeal margin projecting anteriorly as narrow, medially emarginate lobe. Clypeus transversely convex, straight in profile with rather distinct basal margin and frontal triangle. Frontal carinae sinuate with laminate lobes. Central area with short but distinct longitudinal carina. Sides of head in front of eyes moderately convex, behind eyes rounding into convex preoccipital margin. Mesosoma marginate along entire length, margins broken at promesonotal suture and distinctly notched at metanotal groove. Pronotal dorsum moderately convex; humeri armed with broad-based, acute teeth. Promesonotal suture distinct; metanotal groove indicated dorsally by weakly incised line breaking sculpture. Propodeum armed posteriorly with pair of strong, broad-based, triangular, dorsally curved teeth, their posterior margins continued medially but failing to meet, leaving a small gap through which propodeal dorsum meets declivity. Petiole strongly transverse, dorsal margin medially emarginate with pair of distinct, acute, intercalary teeth flanking emargination; lateral spines long and straight with tips weakly curved upwards; dorsal margin between intercalary teeth and lateral spines jagged. Anterior face of first gastral segment very shallowly concave with dorso-medial margin blunt.
Mandibles with very fine shallow punctures. Clypeus very finely, microscopically shagreened, contrasting with rest of head that is finely, but distinctly and regularly striate; striae mostly longitudinal on sides of head, converging medially on vertex. Mesosoma longitudinally striate, striae converging posteriorly on mesonotum and oblique on sides. Both faces of petiole microscopically shagreened. First gastral segment shagreened, a few longitudinal striae on sides.
Dorsum of head with very few erect hairs on anterior clypeal margin, antennal scapes, frontal carinae and area between eyes and posterolateral corners. Mesosomal dorsum with a few erect or semierect, medium length hairs on pronotal humeri, mesonotal and propodeal dorsa and dorsal surfaces of propodeal teeth. Petiole with several short hairs arising from posterior face just below dorsal margin. Dorsum and apex of gaster with more numerous, distinctly longer, golden hairs. Silvery, rather diluted, appressed pubescence on pronotal humeri, dorsum and sides of propodeum, coxae and petiole, more dense and distinctly golden on dorsum of first gastral segment.
Black and glossy. Mandibles and eyes distinctly light reddish-brown. Appendages very dark brown, almost black, inner surfaces of front femora, front and middle tibiae and distal segments of tarsi medium to light reddish brown. Apex of gaster reddish brown.
HOLOTYPE: PAPUA NEW GUINEA, Tatupiti nr Tapini, 1200m, viii.1962, rf., R.W. Taylor acc. 2293 (worker). PARATYPES: data as for holotype (2 workers). Type deposition: holotype in Australian National Insect Collection; 1 paratype each in Museum of Comparative Zoology and Queensland Museum.
Named in honor of my former mentor, Dr Robert W. Taylor, who introduced me to and guided my first steps in my studies on Polyrhachis ants.
- Kohout, R.J. 2007a. Revision of the subgenus Aulacomyrma Emery of the genus Polyrhachis F. Smith, with descriptions of new species (pp. 186-253). In Snelling, R.R., Fisher, B.L. and Ward, P.S. (eds). Advances in ant systematics: homage to E.O. Wilson – 50 years of contributions. Memoirs of the American Entomological Institute. 80:690 pp. PDF