Polyrhachis dives

This is a wide ranging species. Nesting habits seem to be identical throughout the range. P. dives is found in open woodlands and swampy coastal plains, where it builds a characteristic carton structure on the lower branches of trees and shrubs, joining the foliage and twigs with silk to form the nest (Kohout 1988, and see image below).

Identification
A member of the Polyrhachis dives species group.

Kohout (2010) - Throughout its wide distribution, P. dives is a morphologically very stable species with only a few, rather insignificant differences between individuals, even those from widely separated localities. However, south-east Asian specimens generally have a more deeply emarginate anterior clypeal margin and eyes that only rarely exceed the lateral cephalic outline. Most also have the tips of the propodeal spines more distinctly curved outwards and longer petiolar spines that are somewhat curved downwards from their midlength. In contrast, the anterior clypeal margin in Australian and New Guinean specimens is only shallowly emarginate and the eyes clearly exceed the lateral cephalic outline. The propodeal spines are only weakly curved outwards and the petiolar spines somewhat shorter and less curved.

Distribution based on Regional Taxon Lists
Australasian Region: Australia. Indo-Australian Region: Borneo, Guam, Indonesia, Krakatau Islands, Malaysia, New Guinea, Philippines, Singapore. Oriental Region: Cambodia, India, Laos, Myanmar, Thailand, Vietnam. Palaearctic Region: China, Japan.

The distribution of P. dives in Australia is apparently confined to two widely separated areas, one in the Northern Territory (Koolpinyah), and the other in North Queensland (Yarrabah south to Mission Beach). P. dives is very common in suitable habitats in Papua New Guinea, but I have never seen material collected in the Torres Strait islands, on Cape York Peninsula, or south of the Gulf of Carpentaria. The species is only moderately variable, and, although the Australian populations are each apparently well isolated from others, Australian specimens are closely comparable to those from elsewhere (Kohout 1988).

Biology
In Australia P. dives is known from two isolated populations, one in the Northern Territory and the other in northern Queensland. It prefers mostly open savannah woodlands and swampy coastal plains, where it builds its silk and/or carton-based, relatively large, usually polydomous nests between the branches and leaves of small trees and shrubs (Fig. 10C).

Castes
Males and immature stages (eggs, larvae and pupae) deposited in QM spirit collection.

Nomenclature

 *  dives. Polyrhachis dives Smith, F. 1857a: 64 (w.) SINGAPORE. Mayr, 1867a: 49 (q.m.); Wheeler, G.C. & Wheeler, J. 1953e: 208 (l.); Hung, Imai & Kubota, 1972: 1025 (k.). Combination in P. (Myrmhopla): Wheeler, W.M. 1919e: 132. Senior synonym of democles: Forel, 1911e: 298; of euclides, mutiliae: Bolton, 1974b: 173; of exulans: Kohout, 1988c: 433; of vicina: Wang & Wu, 1991: 599; of lucens: Dorow, 1995: 52; of siwiensis: Kohout, 1998: 515. Current subspecies: nominal plus belli, rectispina. See also: Bingham, 1903: 396; Kohout, 2010: 180.
 * affinis. Polyrhachis affinis Smith, F. 1858b: 63 (w.) MYANMAR. [Junior secondary homonym of affinis Le Guillou, above.] Replacement name: vicina Roger, 1863b: 7.
 * democles. Polyrhachis democles Smith, F. 1861b: 40, pl. 1, fig. 9 (q.) INDONESIA (Sulawesi). Junior synonym of dives: Forel, 1911e: 298.
 * mutiliae. Polyrhachis mutiliae Smith, F. 1861b: 39, pl. 1, figs. 15, 20 (w.) INDONESIA (Sulawesi). Combination in P. (Myrmhopla): Emery, 1925b: 197. Junior synonym of dives: Bolton, 1974b: 173.
 * vicina. Polyrhachis vicina Roger, 1863b: 7. Replacement name for affinis Smith, F. 1858b: 63. [Junior secondary homonym of affinis Le Guillou, 1842: 314.] Combination in P. (Myrmhopla): Emery, 1925b: 197. Junior synonym of dives: Wang & Wu, 1991: 599.
 * euclides. Polyrhachis dives var. euclides Forel, 1913f: 202 (w.q.m.) TAIWAN. Junior synonym of dives: Bolton, 1974b: 173.
 * siwiensis. Polyrhachis (Myrmhopla) dives var. siwiensis Santschi, 1932b: 20 (q.) NEW GUINEA. Junior synonym of dives: Kohout, 1998: 515.
 * exulans. Polyrhachis (Myrmhopla) exulans Clark, 1941: 91, pl. 13, fig. 24 (w.) AUSTRALIA. Junior synonym of dives: Kohout, 1988c: 433.
 * lucens. Polyrhachis (Myrmhopla) lucens Donisthorpe, 1947d: 194 (q.) NEW GUINEA. Junior synonym of dives: Dorow, 1995: 52.

Type Material


Polyrhachis democles

Holotype dealate queen in. Labelled “Tond.” (= Tondano, Sulawesi) and with a Donisthorpe type-label.

Polyrhachis mutiliae

Two worker syntypes in. Labelled “Tond.” (= Tondano, Sulawesi), one of them with a Donisthorpe type-label.

Worker
Kohout (2010) - TL c. 5.39-7.71; HL 1.40-1.93; HW 1.18-1.65; CI 84-91; SL 1.56-1.96; SI 119-132; PW 0.87-1.15; MTL 1.87-2.56 (34 measured).

Mandibles with 5 teeth. Anterior clypeal margin with emarginate, shallow, median flange, laterally flanked by acute teeth. Clypeus virtually straight in profile, posteriorly rounding into weakly impressed basal margin. Frontal triangle distict. Frontal carinae sinuate with moderately raised margins. Sides of head in front of eyes weakly convex towards mandibular bases; behind eyes sides widely rounding into rather flat occipital margin. Eyes only moderately convex, in full face view not or only marginally exceeding lateral cephalic outline. Ocelli lacking, relative positions marked by shallow pits in cephalic structure. Mesosoma immarginate. Pronotum rather weakly convex in profile; humeri armed with straight, horizontal, anterolaterally directed, acute spines. Promesonotal suture distinct; mesonotum convex in profile. Metanotal groove poorly indicated; propodeal dorsum armed with slender, obliquely elevated, divergent spines, tips curved upwards and outwards. Petiole with dorsolaterally projecting acute spines that conform to shape of anterior gaster; dorsum medially with pair of distinct intercalary teeth. Anterior face of first gastral tergite higher than full height of petiole, widely rounding onto dorsum of segment.

Mandibles densely and closely longitudinally striate with piliferous pits. Head, mesosoma and petiole distinctly, more-or-less regularly, reticulate-punctate. Sides of mesosoma somewhat more deeply sculptured with numerous pits on meso- and metapleurae. Spines sculptured at bases, smooth and polished towards tips. Gaster finely shagreened.

Mandibles at masticatory borders with numerous, curved, golden hairs and short, appressed hairs towards bases. Anterior clypeal margin with several anteriorly projecting setae medially and a few shorter setae fringing margin laterally. Clypeus with a few, paired, medium length, erect hairs. Apical segments on dorsum and venter of gaster with a number of erect, relatively long, mostly posteriorly directed, golden hairs. Closely appressed, medium length, pale golden pubescence in various densities over most of head and body. Pubescence more silvery on sides of head, mesosoma and petiole. Gastral pubescence somewhat longer, rich golden and more abundant dorsally where it almost completely hides underlying sculpturation; pubescence paler and less dense on gastral venter.

Black, with only condylae and tip of apical antennal segments, light yellowish-brown; mandibular teeth dark reddish-brown.

Queen
Kohout (2010) - TL c. 8.72-9.32; HL 2.03-2.18; HW 1.78-1.90; CI 85-91; SL 1.93-2.09; SI 108-112; PW 1.81-1.90; MTL 2.62-2.74 (14 measured).

Very similar to worker, apart from sexual characters, shorter spines and the following: anterior clypeal margin with median flange more deeply emarginate; clypeus with basal margin virtually flat in lateral view. Eyes more convex, always exceeding lateral cephalic outline. Pronotal spines reduced to minute teeth. Mesoscutum in lateral view relatively high, widely rounding onto flat dorsum with anterior margin evenly rounded in dorsal view; median line bifurcate anteriorly and posteriorly; parapsides flat. Mesoscutellum flat, not elevated above dorsal plane of mesosoma. Metanotal groove distinctly impressed. Propodeal spines very short, directed posteriorly, weakly elevated dorsally. Petiolar spines short, projecting laterally, very weakly curved. Sculpturation, pilosity, pubescence and colour identical to those in worker.