Polyrhachis nepenthicola

The nest of Polyrhachis nepenthicola was collected from the pitcher of Nepenthes stenophylla growing alongside the road in secondary vegetation of the sub-montane, mixed dipterocarp forest. While ant association with various plants is widely known, their interaction with pitcher plants (Nepenthaceae) has been recorded on only a few occasions. Many species of ants visit pitcher plants regularly to feed on the extrafloral nectar; however, they also risk being digested in the pitfall traps. Only one species of ant, Colobopsis schmitzi, is so far known to find a shelter and nesting space within the swollen and hollow tendrils of Nephentes bicalcarata (Clarke and Kitching 1995, Thornham et al. 2012). At the same time, these ants are able not only to move across the slippery surface of the pitcher without being trapped, but also to swim in the pitcher fluid, where they hunt and retrieve food from the pitcher (Clarke and Kitching 1995). However, the nesting behaviour of Polyrhachis nepenthicola, described below, is the only recorded case of an ant actually building its nest within a pitcher of a Nepenthes plant.

Identification
Kohout (2013) - Polyrhachis nepenthicola stands closest to Polyrhachis triaena and also described from Sarawak (Wheeler 1919), with both species sharing a similar size (HL 1.65-1.93 in P. nepenthicola versus HL 1.68-1.78 in P. triaena). However, both species differ in a number of other characters, with P. nepenthicola featuring a distinctly wider head (CI 89-94), shorter antennal scapes (SI 120-128), almost quadrate propodeal dorsum and the conspicuously large propodeal spiracles. In contrast, the head in P. triaena is narrower (CI 82-85), antennal scapes longer (SI 157-159), propodeal dorsum almost 2x as long as wide and the propodeal spiracles relatively flat.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Malaysia.

Castes
Males in spirits collection.

Nomenclature

 *  nepenthicola. Polyrhachis (Myrmothrinax) nepenthicola Kohout, 2013: 49, figs. 1-8 (w.q.m.) MALAYSIA.

Worker
Dimensions (holotype cited first): TL c. 7.26, 6.85-8.47; HL 1.78, 1.65-1.93; HW 1.59, 1.53-1.81; CI 89, 87-94; SL 2.07, 1.93-2.18; SI 130, 120-135; PW 1.00, 0.94-1.15; MTL 2.50, 2.37-2.65 (1+12 measured).

Mandibles with 5 teeth. Anterior clypeal margin widely medially truncate with truncate portion shallowly emarginate and flanked by blunt angles. Clypeus with posteriorly raised median carina; straight in profile, posteriorly rounding into moderately impressed basal margin. Frontal triangle distinct. Frontal carinae sinuate with margins only weakly raised at midlength; central area relatively wide with distinct frontal furrow. Sides of head in front of eyes converging towards mandibular bases in weakly convex line; behind eyes sides widely rounding into convex occipital margin. Eyes convex, in full face view clearly breaking lateral cephalic outline. Ocelli lacking in holotype; median ocellus indicated by shallow pit in some paratypes. Pronotal humeri armed with bluntly terminated, laterally directed, spines, about as long as their basal width; lateral pronotal margins rather blunt, becoming indistinct before reaching promesonotal suture. Mesonotum with lateral margins rounded anteriorly, somewhat raised and subparallel posteriorly towards distinct metanotal groove. Propodeal dorsum only marginally longer than wide, with rather blunt, subparallel, lateral margins, terminating posteriorly in vertically elevated spines; propodeal declivity oblique, laterally expending towards very conspicuous, rather large, propodeal spiracles. Petiole armed with two short, tooth-like, lateral spines and long, acute, dorsoposteriorly elevated median spine, weakly bent upwards from its midlength. Anterior face of first gastral segment distinctly higher than full hight of petiole, widely rounding onto gastral dorsum.

Mandibles very finely longitudinally striate with numerous piliferous pits; sculpture distinctly finer towards masticatory borders. Clypeus very finely reticulate-punctate with rest of head shagreened. Mesosoma and petiole, including spines, distinctly reticulate-punctate, opaque. Gaster very finely shagreened, polished.

Mandibular masticatory borders with numerous, semierect, golden hairs. Clypeus with only few short golden setae along anterior margin and single, medium length hair laterally. A few long, erect hairs on frontal coxae; numerous long hairs lining margins of segments on gastral venter and around apex. Closely appressed golden pubescence rather diluted on head and gaster; it is almost completely absent from mesosoma and petiole.

Black or dark reddish-brown, with head, gaster and appendages a shade lighter; funicular and tarsal segments progressively lighter towards apexes. Mandibles along masticatory borders with narrow, light reddish-brown band.

Queen
TL c. 10.23; HL 2.25; HW 2.03; CI 90; SL 2.59; SI 127; PW 1.65; MTL 3.18 (1 measured). Very similar to worker with usual differences indicating caste, including three ocelli and complete thoracic structure. Pronotal humeri produced into blunt, tooth-like spines; their outer margins merging into rather blunt and short pronotal margins. Mesoscutum virtually as wide as long, with lateral margins converging anteriorly and forming moderately rounded anterior margin; median line only shallowly impressed; parapsides weakly raised along their entire length. Mesoscutum in profile with anterior margin rounded onto virtually flat dorsum. Mesoscutellum convex, distinctly raised above dorsal plane of mesosoma. Propodeal dorsum with lateral margins indistinct; propodeal spines shorter, somewhat anteroposteriorly flattened. Propodeal spiracles similar, but larger, than in worker. Petiole with lateral spines distinctly longer than in worker, almost 2x as long as wide at base; median petiolar spine shorter than in worker, with apex bluntly rounded. Head, mesosoma and petiole finely reticulate-punctate, with anterior margin of mesoscutum medially smooth and polished; gaster shagreened. Pubescence and colour virtually as in worker.

Type Material
Holotype worker: BORNEO, SARAWAK, Lawas, Paya Maga, 04°27’N, 115°33’E, 1810 m, 11.x.2010, T.U. Grafe (worker). Paratypes: data as for holotype, 20 workers, 1 queen, 8 males. Type distribution: Holotype, most paratype workers, paratype queen and paratype males in ; 2 paratypes each in, , , SMKS, UBDG.

Etymology
The specific name is derived from a combination of the generic name of the host pitcher plant, Nepenthes stenophyla, and the Latin suffix -cola, meaning inhabitant.

References based on Global Ant Biodiversity Informatics

 * Kohout R. J. 2013. Polyrhachis (Myrmothrinax) nepenthicola, a new species of the thrinax-group inhabiting pitcher plants (Hymenoptera: Formicidae: Formicinae). Australian Entomologist 40: 47-52.