Polyrhachis boltoni

A diurnally active species that nests arborealy. Heterick & Kitching (2022) collected this species in the canopy of a lowland dipterocarp forest in Brunei.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, Brunei Darussalam, Indonesia, Malaysia.

Biology
From Dorow and Kohout 1995:

With only two partial nests and a relatively small number of individual foragers collected, P. boltoni appears to be rather uncommon. The type-colony nested in the secondary forest area of Ulu Gombak Field Studies Centre. It was situated about 4 m high on a leaf on a tree. The nest was partly sheltered by a torn-off part of the leaf and was built using a coarsely woven silk net to which small pieces of dead leaves, wood fragments up to 4 x 0.1 mm, and other detritus were attached. One nest wall between the parts of the leaf was built from a translucent thin layer of pure silk. The nest comprised one chamber of 3 x 2.5 cm with a height of 1.5 em. The leaf surface in the nest was not lined with a silk layer as is the case in many other species of Polyrhachis. One side of the nest's leaf wall had a fensterfrass (leaf skeletonized by insects leaving one cuticle intact) of 6 x 6 mm. On the nest leaf there were attached several shiny black fungus hyphae (1.5-2 mm in diameter) which were also partly integrated into the nest. In the nest small larvae were attached in clumps on the leaf surface. The nest contained 50 workers, 29 alate females, 9 males and uncounted pupae in cocoons, larvae and eggs.

The second nest was found 1.80 m above the ground on a leaf of a small tree in primary forest near the Field Studies Centre at Pasoh. The nest was attached to the upper side of a dead leaf (17 x 9 cm), which was hanging in the tree attached only by some fungus hyphae of the type mentioned above. It can be assumed that this is not the normal position of the nest, but that it had been damaged recently and was now repaired. The nest measured 6 x 6 cm and consisted of a relatively coarsely woven silk net covered with detritus (pieces of leaves up to 4 x 3 mm, pieces of wood up to 2.5 x 1.5 mm). It contained 85 workers, 21 alate females, 8 males, and uncounted pupae in cocoons, and larvae.

P. boltoni appears to be diurnal. Workers were observed during the daytime on bushes and low herbaceous vegetation collecting detritus from leaves with insect fensterfrass and from rotting pieces of wood. During the night, when the nest was collected, there was no activity. The ants were sitting regularly distributed on the leaf within the partially built nest.

Some interesting conclusions and questions arise from these findings: the fact that no queen was found in the nests leads to the conclusion that P. boltoni is polydomous, as are many other species in Polyrhachis. The two nests mentioned above, with their high numbers of alates, were collected at the end of January and the beginning of February. A dealate queen was collected at the end of February. Further studies should investigate whether P. boltoni queens forage during colony foundation. Further studies are also necessary to determine whether there is a seasonality in colony foundation with nuptial flights after the rainy season in the first quarter of the year, as appears to be indicated by the above data. The findings of the same type of fungus hyphae in and near both nests could indicate that P. boltoni normally nests in the higher parts of trees, possibly in epiphytes or other places, where dead foliage is accumulated and fungi common.

Nomenclature

 *  boltoni. Polyrhachis (Hemioptica) boltoni Dorow & Kohout, 1995: 96, fig. 1 (w.q.) WEST MALAYSIA.

Worker
Dimensions (holotype cited first): TL c. 7.60, 6.35-7.60; HL 1.84, 1.57-1.84; HW 1.28, 1.14-1.28; CI 69, 67-71; SL 2.46, 2.00-2.50; SI 192, 175-203; PW 1.37, 1.12-1.37; MTL 2.71, 2.21-2.71 (17 measured).

Mandibles with 5 teeth, progressively reducing in length towards the base. Clypeus in profile sinuate with posterior margin moderately impressed; the anterior margin arcuate, entire. Frontal carinae prominent with moderately raised lobes, the area between them longitudinally concave; frontal furrow marked anteriorly, lacking posteriorly. Antennal scapes with a distinct bend at their bases. Eyes large, truncate posteriorly, with peculiar posterior blinkers. Face with a distinctly elongated appearance, with the eyes set well back on its sides. Ocelli lacking. Head with well-defined longitudinal lateral carinae commencing on each side at the base of mandible and extending towards the occipital border. These separate the gena from the ventral parts of the cranium. Pronotum with shallow transverse impression behind its collar-like anterior margin; humeri gently rounded. Pronatal dorsum convex, extending posteriorly towards the metanotal furrow as a shield which conceals the greater portion of the mesonotal dorsum. The exposed lateral margins of the mesonotum appear as short, carinate protuberances. Metanotal groove a deeply impressed transverse furrow which reaches on each side to the metathoracic spiracle. Propodeal dorsum twice as long as declivity, gently curved in profile; anterior margin arcuate, feebly medially emarginate, projecting anteriorly towards the pointed posterodorsal extremity of the pronotum, and partly bridging the furrow. Posteriorly the propodeal dorsum is separated from the declivity by a distinct, arch-shaped, transverse carina, which often has a minute median notch or slight interruption; declivity short, gently concave. Petiole with dorsal margin sinuate, lateral angles blunt, indistinct; in side view the petiolar node forms triangle with anterior face almost straight and posterior face slightly convex. Base of first gastral tergite very shallowly truncated.

Mandibles closely shagreened, with numerous piliferous pits, notably towards their external margins. Anterior clypeal margin medially with distinct pits from which a tight cluster of relatively long setae arise. Body dorsally highly polished, at most only very finely microscopically shagreened and shallowly punctate.

Mandibles with numerous short, semierect hairs. Medial portion of anterior clypeal margin with a few relatively long, anteriorly directed setae. Lateral branches of mesosoma and coxae covered with a pile of white, appressed pubescence. Gaster ventrally and around apex with scattered long hairs. The dorsum of the body is virtually hairless, except for some microscopic semierect hairs raising from shallow piliferous pits.

Black throughout; front and middle tibiae sometimes reddish brown.

Queen
Dimensions: TL c. 7.86-8.16; HL 1.84-1.89; HW 1.23-1.28; CI 67-68; SL 2.46-2.56; SI 195-206; PW 1.50-1.62; MTL 2.65-2.87 (12 measured).

Besides the characters identifying full sexuality, including three ocelli, complete thoracic structure and wings, the female resembles the worker very closely. Mesoscutum slightly transverse, 1.25 x wider than long, lateral margins distinctly contracting anteriorly, forming a rather narrowly rounded anterior margin; median line short, parapsides slightly elevated posteriorly; in profile the mesoscutum is relatively low with gently curved dorsum. Mesoscutellum convex, transverse; only slightly elevated above the dorsal plane of mesosoma. Metanotal groove narrow, distinctly impressed. Propodeal dorsum gently sinuate in profile, slightly longer than declivity; posterior margin forming a well defined, arch-shaped transverse carina. The remaining features, including sculpturation, virtual lack of dorsal pubescence and highly polished appearance are the same as in the worker.

Male
Males present in the SMF collection. The larvae were described by Wheeler & Wheeler (1990) as Polyrhachis (Hemioptica) scissa (Roger) and are stored together with pupae in the Wheeler collection (Dorow #933 6 larvae on slides, 9 larvae and 7 pupae in alcohol; Dorow #890 9 larvae on slides).

Type Material
Holotype: Malaysia, Selangor: Ulu Gombak Research Centre, 5.ii.1987 (W.H.O. Dorow #933 (worker). Nidoparatypes: data as for holotype (49 workers, 29 alate females, 9 males and immature stages (eggs, larvae and pupae in cocoons). Paratypes: Malaysia, Negri Sembilan: Pasoh Forest Research Centre, 28.i.1987 (W.H.O. Dorow #890) (85 workers, 21 alate females, 8 males and immature stages (eggs, larvae and pupae in cocoons). Holotype, most nidoparatypes and paratypes deposited in SMF; 8 nidoparatypes (6 workers, 1 alate female, 1 male) and 6 paratypes (4 workers, 1 alate female, 1 male) in QMBA; 2 nidoparatype workers, 2 paratypes (1 worker, 1 female) in each ANIC, BMNH and RMNH; 2 paratype workers in each BPBM, FRIM, MCZC, OXUM and USNM.

References based on Global Ant Biodiversity Informatics

 * Dakir. 2009. The species composition and diversity of ants (Hymenoptera: Formicidae) in mangrove vegetation, in Kolaka, South East Sulawesi and Muara Angke, Jakarta. Thesis of the Graduate School of Agronomic Institute of Bogor. 77 pages.
 * Dorow W. H. O.; and R.J. Kohout. 1995. A review of the subgenus Hemioptica Roger of the genus Polyrhachis Fr. Smith with description of a new species (Hymenoptera: Formicidae: Formicinae). Zool. Meded. (Leiden) 69: 93-104
 * Hashimoto Y., Y. Morimoto, E. S. Widodo, and M. Mohamed. 2006. Vertical distribution pattern of ants in a Bornean tropical rainforest (Hymenoptera: Formicidae). Sociobiology 47(3): 697- 710.
 * Kohout R.J., and M. Mohamed. 2008. A preliminary list of the Polyrhachis ants of the Maliau Basin Conservation area in Sabah, Borneo (Hymenoptera: Formicidae: Formicinae). Asian Myrmecology 2: 63-70.
 * Majer J. D., R. L. Kitching, B. E. Heterick, K. Hurley, and K. E. C. Brennan. 2001. North-south patterns within arboreal ant assembalages from rain forests in Eastern Australia. Biotropica 33(4): 643-661.
 * Pfeiffer M.; Mezger, D.; Hosoishi, S.; Bakhtiar, E. Y.; Kohout, R. J. 2011. The Formicidae of Borneo (Insecta: Hymenoptera): a preliminary species list. Asian Myrmecology 4:9-58
 * Robson Simon Ant Collection, 05-Sept-2014
 * Robson Simon Database Polyrhachis -05 Sept 2014