Polyrhachis erosispina

Identification
Polyrhachis erosispina is very similar to Polyrhachis bellicosa and their distinguishing characters are discussed in the remarks section of the latter species. (Kohout, 2014)


 * Key to the subgenus Polyrhachis workers

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

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)

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.

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
Description by Kohout (2014).

Dimensions (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
Description by Kohout (2014).

Dimensions: 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.

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