Polyrhachis

4 ouvrieres, 2 [[queen]] et 2 [[male]] du releve F 43, Nion, foret sombre, terreau d' Elaeis. Proche de la precedente, mais probablement nouvelle. A reetudier, les collections et documents consultes laissant une incertitude sur les especes de ce groupe.

Formica , pt., Fabr. Syst. Eut. 394 (1775).

Maxillary palpi 6-jointed, elongate; labial palpi 4-jointed; mandibles stout, their inner edge denticulate. Ocelli obsolete in the workers. Thorax more or less armed with spines or hooks; scale of the peduncle incrassate, usually spinose, having two, three, or four spines. Wings with one marginal and two submarginal cells, the discoidal cells obsolete. Abdomen subglobose.

We are indebted to Mr. T. C. Jerdon for the first account of the habits of this genus of Ants; speaking of the F. nidificans , he says: " This Ant makes a small nest about half an inch, or rather more, in diameter, of some papyraceous material, which it fixes on a leaf. I have opened two, each of which contained one female and eight or ten workers. It is very rare, and I have only seen it in Malabar." Since the publication of these remarks, a nest of one of the species has been received from Malacca; it was discovered by Mr. Wallace, and exactly agrees with Mr. Jerdon's description. Pl. IV. figs. 10, 11.

Species of India, the Eastern Archipelago, China, and Philippine Islands. Sp. 1-14.

- [[ worker ]], L. 5,2 a 6 mill. Plus grande et surtout plus robuste que la forme typique. Dents du pronotum plus, fortes, Epines du metanotum courtes (longues comme, la moitie de l'intervalle de leurs bases), extremement larges (aussi larges vers leur base que la moitie de leur longueur), un peu aplaties, mais assez pointues a l'extremite. Epines de l'ecaille courtes, nn peu pins courtes que l'intervalle de leurs bases (beaucoup plus longues chez la hookeri ). Pilosite brune encore plus epaisse, plus setiforme, plus longue et plus obtuse que chez la forme typique et un peu plus abondante,

Une pubescence d'un rouge dore fonce, tres courte et diluee, donne un leger reflet rougeatre au thorax et a la tete. Pubescence de l'abdomen comme chez la hookeri i. sp. Tete et thorax noirs, sans reflet metallique (d'un vert bleuatre metallique splendide chez la forme typique). Bords du thorax et epines luisants; le reste mat ou subopaque. Sculpture, forme, pilosite et couleur du reste identiques a la P. hookeri typique dont elle se rapproche plus, que la, race suivante.

Mackay, Queensland, recoltee par M. Gilbert Turner.

Large or medium-sized ants closely allied to Camponotus .

Worker monomorphic. Head orbicular, oval or rounded subrectangular, very convex above, with very prominent, long and sinuate frontal carinae. Palpi long, the maxillary pair 6-jointed, with the basal about half as long as the second joint, the labial pair 4-jointed. Clypeus well developed, usually convex or more or less carinate. Antennae long, 12-jointed, the scapes inserted some distance behind the posterior border of the clypeus, as in Camponotus ; funicular joints considerably longer than broad. Thorax more or less arcuate above, often more or less carinate on the sides, and more or less dentate of spinose, but exhibiting great differences in conformation in different species. Usually either the pronotum or the epinotum or both are armed with teeth or spines, rarely the mesonotum. The petiole has a large scale, the superior border of which is nearly always armed with pairs of spines or teeth, more rarely also with a median, unpaired spine or tooth. Gaster large, broadly elliptical or subglobular, very convex above, the first segment forming more than half of its surface and often more or less truncated or concave in front. Legs long and well developed, the tibiae often constricted at the base. Gizzard much as in Camponotus .

Female decidedly larger than the worker, with massive thorax. Spines and teeth on the thorax and petiole smaller. Wings long, the anterior pair with a radial and a single cubital cell; discoidal cell lacking and cubital vein usually reaching the outer margin of the wing. Gaster massive, its first segment often proportionally shorter than in the worker.

Male closely resembling the male of Camponotus , small and slender; the thorax and petiole quite unarmed, the latter with a low, thick scale. Frontal carinae more approximated, front more convex, pronotum overarched by the mesonotum. External genital valves small and slender. Cerci distinct.

Pupae enclosed in cocoons.

A large genus comprising several hundred species, many of which are among the most beautiful of ants, confined to the tropics of the Old World, though, like Oecophylla , absent from Madagascar (Map 44). The species of Polyrhachis , however, have a wider range, since a small number of forms occur as far north as Syria in Asia and as far south as the eastern Cape Colony and Tasmania. The majority of the species are aggregated in the Indomalayan, Papuan, and Australian Regions. Forel and I have divided the genus into subgenera, eleven of which, based on peculiarities in the structure of the thorax and petiole, have been recognized up to the present time, namely, Polyrhachis , sensu stricto, Campomyrma Wheeler, Hagiomyrma Wheeler, Myrma Billberg, Hedomyrma Forel, Myrmhopla Forel, Chariomyrma Forel, Myrmatopa Forel, Cyrtomyrma Forel, Myrmothrinax Forel, and Dolichorhachis Mann. In the Ethiopian Region only two of these, Cyrtomyrma and Myrma , are known to occur, the former represented by a very few aberrant species, the latter by a number of forms which show much greater diversity of structure than do the species of the same subgenus in the Indomalayan and Papuan Regions. This fact, together with that of the wide distribution of Myrma , would seem to indicate that it is the most archaic of all the subgenera of Polyrhachis .

The species of Polyrhachis form only moderately large colonies and none of them is sufficiently common to be of economic importance. Many of them are, in fact, rare and sporadic. They are very timid or pacific insects and are most frequently found singly walking up or down tree-trunks or on the foliage of trees or bushes. Their nesting habits are very diverse. According to my observations in Australia, the species of Campomyrma nest in the ground, under stones, or more rarely in crater nests. The same is true of the species of Hagiomyrma and Chariomyrma , though I have always found P. (Hagiomyrma) semiaurata Mayr in large logs and certain species of Chariomyrma in earthen termitaria. So far as known, none of the species of these three subgenera employs silk in the construction of the nest. The species of Hedomyrma , as Mann and I have observed, live in high trees, but we have been unable to find the nests. Several of the larger species of Myrma nest in the ground or in logs and some of them line their nests with silk spun by the larvae. Many of the smaller species of this subgenus make carton and silken nests on or between the living leaves of trees, and this is the general habit also of many species of the subgenera Myrmhopla , Myrmothrinax , Myrmatopa , and Cyrtomyrma . A few species of Myrma and Myrmhopla live in hollow stems or in old galls. Jacobson and Mann have described the beautiful carton and silk nests built by various Myrmatopa species on the under sides of leaves in Java and the Solomon Islands. P. (Myrmhopla) armata of the Indomalayan Region sometimes builds its nest in houses. P. (M.) dives and some of the allied species construct small globular nests of nearly pure silk, somewhat like those of tent-caterpillars, on low bushes. The nest of one of the few species of the subgenus Polyrhachis , sensu stricto, the East Indian P. bihamata , was found by Bingham. "It was of silky, yellowish brown material, placed close to the ground in the center of a clump of bamboos, and measured about a foot in diameter." Some species of Polyrhachis , when irritated, emit a strong, pleasant smell. According to Bingham, the odor of P. (Myrmhopla) venus Forel is like that of the tuberose.

Diagnosis of the subgenus

Worker. Small ants (HL 1.00 - 1.70) with general characteristics of the genus. Anterior clypeal margin arcuate, majority of species with small notch or shallow emargination medially. Frontal carinae sinuate with laminate lobes; frontal triangle usually indistinct or visible only in certain illuminations and views. Eyes ranging from flattened to strongly protuberant. Preoccipital margin with a distinct ridge posteriorly and laterally in all but one species ( decora ), where it is suppressed by overlying cephalic sculpture. Mesosoma with dorsum showing all stages from fully marginate to completely immarginate. Pronotal humeri armed with spines, teeth or simply angular. Promesonotal suture present. Mesonotal and propodeal dorsa virtually fused. Metanotal groove completely lacking or only very weakly indicated by a hairline break in dorsal sculpture and / or by shallow incisions of lateral margins in species with marginate mesosoma. Propodeum terminating posteriorly in a pair of short teeth, tubercles or simply rounded, except in one species ( wilsoni ), where it is armed with long, mostly outwardly directed spines. Petiole scale-like; dorsal margin acute, usually entire, but occasionally with intercalary teeth or short spines, medially emarginate or unevenly jagged, laterally armed with short spines or teeth. In several species ( decora and its allies) petiole deeply transversely sculptured with dorsal margin more-or-less blunt. Base of first gastral segment usually concave medially, accomodating posterior face of petiole; dorsal margin of concavity acute or blunt and often raised above dorsum of segment; first gastral segment sometimes truncate or simply convex. Sculpture of head and body mostly consisting of regularly spaced striae that are either longitudinal or convoluted producing a characteristic “ geometrical ” appearance; gastral sculpture more modest, usually consisting of longitudinal striae; most distinct on sides of first gastral segment.

Queen. Very much like worker with usual characters identifying full sexuality, including three ocelli and complete thoracic structure with wings. Armament of pronotal humeri somewhat reduced, lateral petiolar spines distinctly shorter. Sculpture of head and body similar to that of worker, pattern of striation following structural characteristics of fully developed mesosoma.

Male. A single associated male is known for only one species (wardi) and as such has been omitted from this work. Hung (1967) studied the male genitalia of Polyrhachis and noted that they proved to be quite similar throughout the genus.

Distribution and biology. The known distribution of the subgenus ranges from the islands of eastern Indonesia (Aru, Misool), across the New Guinean mainland and adjacent islands (Umboi) to the Bismarck Archipelago, including New Britain and New Ireland. Little is known about their biology and nesting habits, however, a small colony of P. dohrni was collected by the author from a dry hollow twig on a living tree at the edge of lowland rainforest. The internal walls of the twig cavity were lined with a little silk. The only other record of a nest is of P. wardi , collected by Dr Phil Ward, also from a dry twig of a rainforest tree. The colonies of both species were rather small, with only a few workers (5 and 11 respectively, including 2 and 3 alate queens and a single male). If such a nesting pattern is the norm for other species of the subgenus, that might explain the general scarcity of Aulacomyrma material even in the best collections. This might also account for the fact that all previously described species were based on unique specimens. In spite of the exemplary cooperation of the listed institutions, this situation has only marginally improved in this revision with almost half the new species described from single specimens.

Body more or less armed with spines. Antenna elongate, usually nearly as long as the body; labial palpi 4-jointed, the basal joint shortest, the three following, each in succession, longer than the preceding; the apical joint three times the length of the basal one. Maxillary palpi 6-jointed, elongate, the basal joint short, about half the length of the second joint, each of the following joints more than twice the length of the second joint. Thorax: subovate in the females; compressed and frequently flattened above in the workers; wings as in Formica ligniperda . Abdomen globose. (Details, Plate I.)

This genus of Ants, of which the Formica bihamata may be regarded as the type, forms a very distinct section of the Formicidae: the males I am not acquainted with. The habit of these insects is arboreal, as we learn from Mr. Jerdon, who, in his paper on Ants, in the Madras Journal, describes two species; of one, P. nidificans , he says, " This Ant makes a small nest about half an inch or rather more in diameter, of some papyraceous material, which it fixes on a leaf; I have opened two, each of which contained one female and eight or ten workers. It is veryrare; I have only seen it in Malabar." What can be the use of the formidable spines and hooks with which these creatures are armed, it is impossible to determine; on examination we find, as might be expected in species living on trees, and probably all have the same habit, that the legs are destitute of spines, and usually of pubescence also; the calcaria at the apex of the tibiae are very short, and the tips of the tarsal joints have very short spines and hairs.

The Polyrhachis textor , described in these papers, was captured with its nest, and was sent from Malacca by Mr. Wallace; the nest is nearly oval, not quite an inch in length, its shortest diameter being a little over half an inch; this nest is not of a papyraceous texture, but fibrous, formed, as it were, of a coarse network; the colonies must consequently be very small, as Mr. Jerdon says, consisting of only eight or ten individuals; but probably at the height of the season, when the males appear, the nests may be somewhat enlarged, as we know to be the case amongst the social Wasps.

Although these insects are usually rare, or at least seldom met with in collcetions, Mr. Wallace has captured no less than nineteen species in the East: from the New World I have only seen one or two, about four from Africa, and the same number from Australia.

Polyrhachis is a genus of formicine ants found in the Old World with over 600 species. The genus is yet to be comprehensively resolved and contains many varied species including nest-weavers (e.g. Polyrhachis dives), swimming workers (e.g. Polyrhachis sokolova), soil (e.g. Polyrhachis proxima) and tree-dwellers (e.g. Polyrhachis bicolor).