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).

This species is a relatively rare species towards the northern limits of its distribution (Philippines, Malaysia and Borneo), where the very similar and rather common Polyrhachis olybria is often misidentified as P. bellicosa (see Kohout 1998: 508-509). Polyrhachis bellicosa is much more common in New Guinea, where it occurs sympatrically with Polyrhachis erosispina (Kohout, 2012).

Identification
The relationship and differences between both species were discussed in detail by Kohout (1988: 418-422).

Distribution
This taxon was described from Indonesia (Aru Island). It is also found in Philippines, Malaysia, New Guinea and Australia.

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.
 * crudelis. Polyrhachis bellicosa var. crudelis Emery, 1887a: 238 (w.) INDONESIA (Morotai I.). Junior synonym of bellicosa: Hung, 1970: 5.

Polyrhachis bellicosus type material.

Holotype worker. Type locality: INDONESIA, Aru I. (A.R. Wallace), (examined by Kohout, 2012).

Polyrhachis bellicosa crudelis type material.

Syntype workers. Type locality: INDONESIA, Mortly I. (= Morotai) (Gribodo), (examined by Kohout, 2012).

Type Material


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 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 bellicosa and 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.

Worker
Kohout (1988):

DIMENSIONS OF HOLOTYPE TL 8.98; HL 2.06; HW 1.75; CI 85; (antennae missing); PW 1.03; MTL 3.65; PeH 1.78; PeI 86.

DIMENSIONS Workers: TL 7.30-8.52; HL 1.80-2.12; HW 1.56-1.96; CI 83-97; SL2.27-2.72; SI 132-154; PW 0.86-1.01; MTL 3.07-3.68; PeH 1.64-2.07; PeI 87-98 (50 workers measured). Females: TL 9.77-10.08; HL 2.12-2.22; HW 1.56-1.66; CI 74-76; SL2.95-3.02; SI 181-189; PW 1.41-1.51; MTL 3.93-4.03; PeH 1.11-1.21; PeI 51-57 (10 females measured).

Additional References

 * Kohout, R.J. 2012. A review of the Australian Polyrhachis ants of the subgenera Myrma Billberg, Myrmatopa Forel, Myrmothrinax Forel and Polyrhachis Fr. Smith (Hymenoptera: Formicidae: Formicinae). Memoirs of the Queensland Museum – Nature 56(1): 25-59.