Polyrhachis bellicosa

The nesting habits of P. bellicosa appear highly diverse with collection records listing terrestrial, lignicolous and arboreal nesting sites. Two nests located at Iron Range on Cape York Peninsula were both situated about 2-4 metres above the ground and attached to tree trunks using lianas and a strong network of tendrils from other climbers for support. The nests consisted of various vegetation debris bound together by a yellowish-brown silk (Kohout 1988a, 1999; Robson & Kohout 2005, 2007; Kohout, 2012).

Polyrhachis bellicosa appears to be a New Guinean species which extended its range into Indonesia, Malaysia, southern Philippines and northern Australia. It is a relatively common species throughout the New Guinean mainland where it occurs sympatrically with Polyrhachis erosispina; however, it becomes relatively rare towards the northern limits of its distribution, where it is mostly replaced by Polyrhachis olybria (specimens of which are often misidentified as P. bellicosa, see Kohout 1998: 508-509). (Kohout, 2012, 2014)

Identification
Kohout (2014) - Polyrhachis bellicosa is one of three species (the other two are Polyrhachis erosispina and Polyrhachis olybria) which are frequently misidentified. However, P. olybria is easily separable by a number of characters of which the most conspicuous is the lightly coloured first gastral segment which ranging from light yellowish-brown to medium reddish-brown. Additionally, the posterior angles of propodeal dorsum in P. olybria are produced into short, acute, dorsoposteriorly directed spines, which are contiguous at their bases, forming a ‘V’ when the propodeum is viewed from behind. Ocelli usually lacking in workers of P. olybria, with only their relative position usually marked by shallow depressions in cephalic sculpturation. In contrast, in P. bellicosa and P. erosispina the gaster is uniformly black, or very dark reddish-brown, the posterior angles of propodeal dorsum terminate in medially directed, short, transverse ridges and ocelli are always present, though the lateral pair is sometimes obscure. While the differences separating P. olybria from both the other species are clearly defined, those separating P. bellicosa and P. erosispina can be very tenuous, due to apparent character displacement (see above). Some of the more reliable diagnostic characters of P. bellicosa include the more convex eyes which, in full face view, clearly exceed the lateral cephalic outline, the very fine microsculpture of the body, especially on pronotal dorsum which is very smooth and almost polished, and short or medium length hairs are rather sporadic and virtually absent from all dorsal body surfaces. In contrast, in P. erosispina the eyes are only moderately convex and do not or only marginally exceed the lateral cephalic outline in full face view, the microsculpture of the body is coarser, notably on pronotal dorsum, which is sub-opaque, lacking a polished appearance and there are usually abundant short to long hairs over all body surfaces. Most specimens of P. bellicosa and P. erosispina differ in size and despite some overlap in their head lengths (HL 1.79 – 2.12 in P. bellicosa versus 2.02 – 2.39 in P. erosispina) specimens of the former are usually smaller than the latter.

Distribution based on Regional Taxon Lists
Australasian Region: Australia. Indo-Australian Region: Borneo, Indonesia, Malaysia, New Guinea, Philippines. Oriental Region: Thailand.

Polyrhachis bellicosa is the only member of the nominal subgenus that occurs in Australia. Its distribution extends from south-east Asia to Indonesia, New Guinea and south to Cape York Peninsula in Queensland (Kohout, 2012).

Biology
Kohout (1988) - Nests of P. bellicosa are somewhat similar to those of Polyrhachis erosispina. They are, however, always situated relatively high in the vegetation, often some 3 to 5m above the ground. A few have been observed between clumped leaves of bamboo, but the great majority are constructed between lianas and other climbers pressing against tree trunks. The walls of these nests are normally supported by a strong network of tendrils from surrounding climbing vines, and incorporate other vegetation debris bounded with yellowish-brown silk. Some of the nests observed were quite huge. One in particular measured close to 50cm across and must have contained thousands, if not tens of thousands, of ants. The surrounding vegetation and forest floor was virtually covered by a network of trails with numerous foraging workers.

Nests always contain one queen.

Nomenclature

 *  bellicosa. Polyrhachis bellicosus Smith, F. 1859a: 142 (w.) INDONESIA (Aru I.). Hung, 1970: 7 (m.); Kohout, 1988b: 418 (q.); Wheeler, G.C. & Wheeler, J. 1990b: 762 (l). Subspecies of bihamata: Mayr, 1862: 678. Revived status as species: Mayr, 1867a: 50. Senior synonym of crudelis: Hung, 1970: 5. See also: Kohout, 2012: 55; Kohout, 2014: 6.
 * crudelis. Polyrhachis bellicosa var. crudelis Emery, 1887a: 238 (w.) INDONESIA (Morotai I.). Junior synonym of bellicosa: Hung, 1970: 5. See also: Kohout, 2014: 10.

Type Material


Polyrhachis bellicosus - Holotype worker in. Labelled “Aru 32” (= Aru I., New Guinea) and with a Donisthorpe type-label.

Kohout (1988) - There are two forms of the petiolar column in workers of P. bellicosa. The holotype exhibits the least common of these, in which the anterior section at the immediate base of the spines is swollen. Petiolar segments of such structure are rare among other specimens. Only a small percentage of workers in any particular population show this remarkable configuration, and specimens intermediate to the more usual unswollen condition are uncommon. The swollen condition has been observed in populations of P. bellicosa from various parts of Papua New Guinea, but only where this species is sympatric with its closely related counterpart, Polyrhachis erosispina.

The preceding was first perceived during field studies, and has been subsequently confirmed for other areas using previously collected material. It is obviously repeated under the same circumstances of contact with P. erosispina in populations of P. bellicosa in eastern Indonesia and in the Philippines. A worker of P. bellicosa with a swollen petiole was, for example, discovered in material containing both species from Nabire, Irian Jaya. Presence of the phenomenon on Aru Island is confirmed by the holotype itself, and documentation of the presence of P. erosispina by Karawajew (1927). The Philippine record is from Mindanao, where a worker with swollen node was collected with 'normal' specimens at the same locality as another undescribed species of the subgenus — a species closely related both to P. bellicosa and P. erosispina.

On the other hand, I have never observed the swollen petiolar condition in Australian populations of P. bellicosa despite careful examination of many hundreds of specimens. I believe this to be significantly correlated with the absence of any other closely related species in Australia. Indeed, no other species of subgenus Polyrhachis, whether related to bellicosa or not, is known from that continent. It is unfortunate, from the taxonomic point of view, that this remarkable feature is relatively rare, for it is the most constant and reliable character identifying P. bellicosa, even when other characters fail to distinguish the species from sympatric erosispina specimens.

Kohout (2014) - Hung (1970) considered P. bellicosa var. crudelis a synonym of the nominal species, but after examining the single available syntype, I believe it could be a synonym of P. erosispina, rather than P. bellicosa. Although the syntype has distinctly convex eyes that clearly exceed the lateral cephalic outline in full face view, like those of P. bellicosa, in other characters it resembles specimens of P. erosispina. The lanceolate bases of mesonotal spines and distinctly coarser body sculpturation combined with abundant pilosity and pubescence of the specimen of crudelis closely resembles specimens of P. erosispina, but it does differ somewhat in having a more massive petiolar node. However, having only a single syntype available and no other specimens of P. bellicosa var. crudelis apparently known, I am reluctant to make any changes to its present status as a synonym of P. bellicosa. Considering that at the time of the description of crudelis, P. erosispina had not been described, it was logical that Emery has decided to place it as a variety of the closely similar P. bellicosa.

Worker
Description by Kohout (2014).

Dimensions (holotype cited first): TL c. 8.98, 7.30 – 8.98; HL 2.06, 1.79 – 2.12; HW 1.75, 1.56 – 1.96; CI 85, 83 – 97; SL (antennae missing), 2.27-2.72; SI -, 132 – 157; PW 1.03, 0.86 – 1.03; PeH 1.78, 1.64 – 2.07; PeI 86, 87 – 108; MTL 3.65, 3.07-3.68 (1+52 measured).

Dimensions (syntype of crudelis): TL c. 8.37; HL 2.03; HW 1.72; CI 85; SL 2.71; SI 157; PW 0.94; PeH 2.31; PeI 114; MTL 3.53 (1 measured).

Mandibles with 5 teeth, distinctly reducing in length towards mandibular base. Anterior clypeal margin arcuate. Clypeus with blunt, posteriorly raised, median carina; clypeus convex in profile with moderately impressed basal margin. Frontal triangle distinct. Frontal carinae sinuate with distinctly raised margins; central area with longitudinal carina instead of usual frontal furrow. Sides of head in front of eyes converging into mandibular bases in weakly convex line; behind eyes, sides widely rounding into relatively narrow occipital margin. Eyes convex, in full face view clearly exceeding lateral cephalic outline. Median ocellus present; lateral ocelli obscure or lacking in some specimens. Pronotal humeri armed with relatively long, acute, anterolaterally and weakly ventrally directed spines; outer borders of spines continuous basally with rather blunt, weakly rounded lateral pronotal margins that terminate before reaching strongly impressed promesonotal suture. Mesonotal dorsum with lateral margins strongly raised into pyramidal, rather compressed, dorsoposteriorly projecting spines, with tips mostly subparallel, but sometimes curved outwards or downwards. Metanotal groove indistinct dorsally, weakly impressed laterally. Propodeal dorsum immarginate with posterior angles produced into short, medially unconnected, transverse ridges; propodeal declivity distinctly shorter than propodeal dorsum. Petiole columnar, dorsally with a pair of hook-shaped spines. Anterior face of first gastral segment widely rounding onto dorsum.

Mandibles finely, longitudinally striate with numerous piliferous pits. Head, including clypeus, reticulate-punctate, semipolished. Pronotal dorsum very finely reticulate-punctate, polished; mesonotum, propodeum and petiole finely reticulate-punctate, tips of spines smooth and highly polished. Gaster finely shagreened, moderately polished.

Mandibular masticatory borders with a few golden hairs. Anterior clypeal margin with several medium length, golden setae medially and fringe of shorter setae laterally. A single pair of medium length, golden hairs medially at anterior margin of clypeus. A few, medium length, golden hairs on fore coxae and brush of short, golden hairs, on subpetiolar process. Gaster with numerous, moderately long hairs on venter and around apex. Hairs completely absent from antennal scapes and all dorsal body surfaces. Closely appressed, golden pubescence distributed over most body surfaces, except pronotal dorsum and spines.

Colour. Head, including mandibles and antennae, tips of spines, distal ends of femora, tibiae, tarsi and gaster black; pronotal and mesonotal lateral margins narrowly bordered with black or dark brown. Mesosoma, most of petiole, coxae and femora, except their distal ends, light reddish-brown.

Queen
Description by Kohout (2014).

Dimensions: TL c. 9.77-10.08; HL 2.12-2.22; HW 1.56-1.66; CI 74-76; SL 2.95-3.02; SI 181189; PW 1.41-1.51; MTL 3.93-4.03; PeH 1.111.21; PeI 51-57 (10 measured).

Distinctly larger than worker and with usual characters identifying full sexuality, including three ocelli, complete thoracic structure and wings. Mandibles with four teeth; apical tooth much longer than other teeth which are greatly reduced or often vestigal. Eyes distinctly larger; sides of head in front of eyes virtually parallel towards mandibular bases. Frontal triangle distinct; frontal carinae sinuate with distinctly raised margins; central area concave with finely impressed frontal furrow. Pronotal spines distinctly shorter, only about 2× as long as their basal width. Mesoscutum only marginally wider than long; lateral margins converging anteriorly into moderately rounded anterior margin; median line distinct; parapsides flat; mesoscutum in profile relatively high, anterior face widely rounding onto flat dorsum. Mesoscutellum moderately convex, only marginally elevated above dorsal plane of mesosoma. Propodeal dorsum not marginate, rather flat in outline, marginally longer than declivity; posterior angles forming upturned, medially directed, rounded ridges with propodeal dorsum between them descending into declivity in medially uninterrupted line. Petiole with pair of rather slender, relatively long, widely diverging spines with their extreme tips curved backwards and weakly downwards.

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

Mandibles at masticatory borders with several golden hairs. Anterior clypeal margin with several longer setae medially and fringe of shorter setae laterally. A single pair of medium length, golden hairs medially near anterior margin of clypeus. Several longer hairs on fore coxae and brush of short, golden hairs, lining subpetiolar process. Relatively long, golden hairs on venter and around apex of gaster. Very fine, closely appressed, silvery pubescence in various densities over most body surfaces; pubescence somewhat longer on sides of mesosoma and virtually absent from spines of petiole.

Colour. Black, with mandibles, pronotal collar, subpetiolar process and legs, except apical tarsal segments, light to medium reddish-brown. Antennae, including condylae, medium to dark reddish-brown, extreme tip of apical funicular segment light, reddish-brown.

Male described by Hung (1970); immature stages in ANIC and QMBA spirit collections.