Polyrhachis (subgenus)

This is the nominal subgenus of Polyrhachis.


 * Key to Polyrhachis gravis species-group workers

Species Groups
bihamata group - Dorsum of mesosoma distinctly laterally marginate along its entire length; propodeal dorsum terminating in a pair of elongated, posteriorly directed, dorsally flattened, blunt spines
 * Polyrhachis bellicosa
 * Polyrhachis erosispina
 * Polyrhachis maliau
 * Polyrhachis mindanaensis
 * Polyrhachis montana
 * Polyrhachis olybria
 * Polyrhachis taylori
 * Polyrhachis ypsilon

lamellidens group - Dorsum of mesosoma distinctly laterally marginate along its entire length; propodeal dorsum terminating in a pair of elongated, posteriorly directed, dorsally flattened, blunt spines
 * Polyrhachis craddocki
 * Polyrhachis lamellidens

Distribution and biology
The known distribution of the subgenus Polyrhachis extends throughout Southeast Asia, from Japan and China in the east to Myanmar and India in the west, extending south to the Philippines, Borneo, Indonesia and New Guinea where it reaches as far east as the Bismarck Archipelago and to northern Australia in the south. Members of the subgenus are mostly arboreal, building nests of silk and vegetation debris against tree trunks, or lignicolous. Nests of some species (e.g. P. bellicosa) are situated relatively high off the ground (often 3 – 5 m), between lianas and other climbers, with the walls of the nest usually supported by a strong network of tendrils from surrounding climbing vines. Some nests, however, are located close the ground, usually against a tree trunk and incorporating the foliage and shoots of climbers and multiple stems of woody lianas (e.g. P. erosispina, P. bihamata). However, in areas with abundant bamboo, some species evidently prefer to nest inside dead, dry bamboo stems (e.g. P. erosispina, P. taylori), with the nest usually occupying several internodes (Kohout, 1988, 1998). The only apparent exceptions to the arboreal nesting habits of the subgenus are P. lamellidens and P. olybria, both of which have been recorded nesting in the ground or in rotten logs (Yano, 1911; Robson & Kohout, 2005, 2007).

Nomenclature

 *  POLYRHACHIS [Formicinae: Camponotini]
 * Polyrhachis Smith, F. 1857a: 58. Type-species: Formica bihamata, by original designation.

Kohout (2014):

Worker
Medium-sized to relatively large ants (HL 1.78 – 2.90) with general characteristics of the genus. Head oval; eyes only moderately convex, in full face view not reaching (as in P. bihamata or P. craddocki), only touching (as in P. olybria or P. lamellidens) or clearly exceeding lateral cephalic outline (as in P. bellicosa or P. taylori); median ocellus distinct (as in P. bellicosa or P. bihamata) or obscure or absent (as in P. olybria or P. lamellidens); lateral ocelli present only in some specimens of several species (e.g. P. bellicosa and P. erosispina). Mesosoma distinctly laterally marginate (lamellidens-group) or immarginate (bihamata-group); pronotal spines virtually straight (as in P. bellicosa or P. taylori) or hook-shaped (as in P. bihamata or P. ypsilon); mesonotum with almost pyramidal or lanceoloate, posteriorly projecting spines in most species (bihamata-group) or with dorsally raised lateral margins terminating in short, acute spines (lamellidens-group) (Fig. 33). Propodeal dorsum terminating posteriorly in short, upturned spines (as in P. olybria) (Fig. 23), medially directed short ridges (as in P. bellicosa or P. erosispina), or posteriorly directed, dorsally flat, blunt spines (as in P. craddocki and P. lamellidens) (rather similar to those in P. hexacantha- or rastrata-group species of the subgenus Campomyrma Wheeler). Petiole columnar, bearing a pair of hook-shaped, somewhat flattened spines, more-or-less divergent from their bases (as in P. ypsilon or P. lamellidens), or subparallel (as in 'P. bihamata' or P. craddocki).

Queen
In addition to being distinctly larger in size and possessing the usual sexual characters, queens are very dissimilar to workers. Mesonotal spines are absent from the fully developed mesosoma with wings and the petiolar spines are greatly reduced and simply pointed, resembling those of queens of other subgenera (e.g. Myrmhopla Forel).

Male
Male of only a few species are known and as such, their treatment has not been attempted here. Donisthorpe (1942) described a male of P. bihamata and Hung (1970) described the males of P. bellicosa and P. lamellidens. However, as mentioned by Hung (1970), the single male considered by Donisthorpe to be that of P. bihamata was without associated workers and, consequently, its identity is questionable. Also, because Hung’s interpretation of P. bellicosa encompassed three currently recognised species (P. bellicosa, P. erosisipina and P. olybria), the specific identity of the male specimen he described cannot be confirmed.