Polyrhachis erosispina

Specimens have been collected in "wet forest" and rainforest.

Identification
A member of the bihamata group of the subgenus Polyrhachis. Kohout (2014) - Polyrhachis erosispina is very similar to Polyrhachis bellicosa; 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.


 * Key to the subgenus Polyrhachis workers

Distribution
The known distribution of P. erosispina encompasses only the New Guinean mainland and several eastern Indonesian islands, including Sulawesi. To date it is unknown from the Bismarck Archipelago and Cape York Peninsula in Queensland. (Kohout, 2014)

Distribution based on Regional Taxon Lists
Indo-Australian Region: Indonesia, New Guinea.

Biology
Kohout (1988) - A nest was located on the edge of the primary forest, some 1.5m above the ground. It measured approximately 20cm in diameter, and was constructed between twisting multi-stems of a woody liana and the adjacent tree trunk. Its walls incorporated the foliage and shoots of an abundant tendril climber. This nest followed the basic structural design observed in Polyrhachis erosispina throughout Papua New Guinea, and was typical in its situation in the lower arboreal zone. In areas with abundant bamboo growth erosispina, together with many other Polyrhachis species (of subgenera other than Polyrhachis), normally nests in bamboo internodes, much as was the case with the Polyrhachis taylori type colony.

Nests always contain one queen.

Castes
Male in ANIC and QMBA spirit collections; immature stages unknown.

Nomenclature

 *  erosispina. Polyrhachis bellicosa var. erosispina Emery, 1900d: 713 (footnote) (w.) NEW GUINEA. Karavaiev, 1927e: 12 (q.). Junior synonym of bellicosa: Hung, 1970: 5. Revived from synonymy and raised to species: Kohout, 1988b: 419.

Worker
Kohout (2014) - (lectotype cited first): TL c. 9.07, 8.01 – 9.37; HL 2.18, 2.02 – 2.39; HW 1.93, 1.69 – 2.09; CI 89, 82 – 91; SL 2.81, 2.52 – 3.02; SI 146, 135 – 150; PW 1.15, 0.93 – 1.16; PeH 2.09, 1.81 – 2.17; PeI 96, 84 – 97; MTL 3.69, 3.43 – 4.08 (1+53 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 relatively flat with frontal furrow almost reaching median ocellus. Sides of head in front of eyes converging into mandibular bases in convex line; behind eyes, sides widely rounding into relatively narrow occipital margin. Eyes only moderately convex; in full face view usually not or only marginally exceeding lateral cephalic outline. Median ocellus present; lateral ocelli often 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 margins that terminate before reaching strongly impressed promesonotal suture. Mesonotal dorsum with lateral margins strongly raised into lanceolate, somewhat dorsomedially compressed, dorsoposteriorly projecting spines with tips often variously ‘gnawed’ and curved outwards or downwards. Metanotal groove weakly impressed. Propodeal dorsum immarginate with posterior angles produced into short, medially unconnected, transverse ridges; propodeal declivity shallowly concave, distinctly shorter than propodeal dorsum. Petiole columnar, bearing a pair of subparallel, hook-shaped spines. Anterior face of first gastral segment widely rounding onto dorsum.

Mandibles finely, longitudinally striate with numerous piliferous pits. Head, mesosoma and petiole reticulate-punctate, opaque; tips of spines smooth and highly polished. Gaster finely shagreened.

Mandibular masticatory borders with a few, curved, golden hairs. Anterior clypeal margin with several medium length, golden setae medially and fringe of shorter setae laterally. A few paired, relatively short, golden hairs on clypeus, along frontal carinae and on vertex; brush of short erect hairs behind eyes towards occipital margin, clearly exceeding cephalic outline in full face view. Numerous medium length, golden hairs on fore coxae, anterior face of petiole and brush of extremely short, golden hairs on subpetiolar process; occasionally short hairs present on bases and along pronotal and mesonotal spines. Gaster with numerous, short hairs on anterior face of first gastral tergite; abundant moderately long hairs on venter and around apex of gaster. Hairs completely absent from antennal scapes. Closely appressed, golden pubescence distributed over most body surfaces, except tips of spines.

Colour. Head, including mandibles and antennae, apical half 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 most of femora light reddish-brown.

Queen
Kohout (2014) - TL c. 10.98 – 12.14; HL 2.52 – 2.72; HW 2.07 – 2.32; CI 80 – 85; SL 3.38 – 3.78; SI 156 – 176; PW 1.56 – 1.79; MTL 4.23 – 4.69; PeH 1.16 – 1.41; PeI 43 – 51 (20 measured).

Queen distinctly larger than worker with usual characters identifying full sexuality, including three ocelli, complete thoracic structure and wings. It was described at length by Karavaiev (1927: 12) and Kohout (1988: 419) and details are not repeated here. The queen of P. erosispina is somewhat similar to that of P. bellicosa, but they are easily separated by their size (HL 2.52 – 2.72 in erosispina versus HL 2.12 – 2.22 in bellicosa) and the shape of their head and petiole.

Type Material
Lectotype and paralectotypes (designated by Kohout, 1988: 419). Type locality: NEW GUINEA: Ramoi (Beccari); INDONESIA: SULAWESI (as Celebes), Kandari (O. Beccari), (examined).