Polyrhachis olybria

Polyrhachis olybria is a relatively common species known from Thailand, peninsular Malaysia and Singapore, south to Borneo, Sumatra and Java and as far east as the Philippines.

Identification
Workers of P. olybria are relatively similar to those of Polyrhachis bellicosa and Polyrhachis erosispina with their relationship and distinguishing characters discussed in remarks section of P. bellicosa and also in detail by Kohout (1998: 508). Polyrhachis olybria differs from both other species by its reddish-brown first gastral tergite and the acute, dorsoposteriorly projecting, propodeal spines. Also, the outline of clypeus in profile of P. olybria is evenly convex, while the summit of convexity in the other two species is distinctly higher and closer to the base of clypeus. The sides of head behind the eyes in P. olybria are only weakly convex before converging towards the occipital margin in virtually straight line, while in other two species, the sides of the head behind the eyes are distinctly convex throughout their length. With respect to queens, the dorsa of the mesoscutum and mesoscutellum in P. olybria are covered with numerous short to medium length hairs, which are distinctly less abundant in P. erosispina and completely absent in P. bellicosa.

Specimens from Sumatra are rather similar to those from peninsular Malaysia in being generally darker in colour and having their pronotal spines relatively straight and only weakly bent downwards. In contrast, specimens from Sabah are distinctly lighter in colour and have the tips of their pronotal spines usually curved downwards and weakly backwards. Despite this variation, specimens from across the entire distribution are closely similar in most other aspects and I believe all are conspecific. (Kohout, 2014)


 * Key to the subgenus Polyrhachis workers

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, Brunei Darussalam, Indonesia, Malaysia, Philippines, Singapore. Oriental Region: Thailand.

Nomenclature

 *  olybria. Polyrhachis olybrius Forel, 1912n: 73 (q.) INDONESIA (Sumatra). Combination in P. (Myrmhopla): Emery, 1925b: 197; in P. (Polyhachis): Kohout, 1998: 508.

Worker
Description by Kohout (2014).

Dimensions (topotype cited first): TL c. 8.87, 8.11 – 9.88; HL 2.06, 1.96 – 2.46; HW 1.78, 1.75 – 2.06; CI 86, 84 – 89; SL 2.71, 2.34 – 3.09; SI 152, 144-155; PW 0.97, 0.94 – 1.15; PeH 2.29, 2.12 – 2.56; PeI 111, 107 – 121; MTL 3.58, 3.43 – 3.78 (1+22 measured).

Mandibles with 5 teeth, distinctly reducing in length towards mandibular base. Anterior clypeal border arcuate. Clypeus with blunt, posteriorly raised, median carina; clypeus convex in profile with only weakly impressed basal margin. Frontal triangle distinct. Frontal carinae sinuate with distinctly raised margins; central area relatively flat with frontal furrow. Sides of head in front of eyes converging into mandibular bases in weakly convex line; behind eyes, sides weakly convex before converging into relatively narrow occipital margin in virtually straight line. Eyes only moderately convex, in full face view usually not or only marginally exceeding lateral cephalic outline in some specimens. Median ocellus present in some specimens but usually obscure or lacking; lateral ocelli lacking with relative positions indicated by minutely raised cephalic sculpturation. Pronotal humeri armed with moderately long, acute, anterolaterally and somewhat ventrally directed spines; outer borders of spines continuous basally with rather blunt, weakly rounded lateral margins that terminate before reaching well impressed promesonotal suture. Mesonotal dorsum with lateral margins strongly raised into almost pyramidal, rather compressed, posterodorsally projecting spines, with tips subparallel or weakly curved outwards. Metanotal groove poorly indicated. Propodeal dorsum without any traces of lateral margins, posterior angles produced as short, acute, dorsoposteriorly directed spines, that are contiguous at bases and form a ‘V’ when viewed from behind; propodeal dorsum about 1.5× longer than weakly concave declivity. Petiole columnar, bearing a pair of slender, subparallel, dorsally 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 golden hairs. Anterior clypeal margin with several medium length, golden setae medially and a fringe of only marginally shorter setae laterally. A few pairs of medium length, golden hairs on clypeus, along frontal carinae and on vertex and occipital corners. A few, medium length, golden hairs on fore coxae; gaster with numerous, moderately long hairs on venter and around apex. Hairs completely absent from antennal scapes and all dorsal body surfaces. Closely appressed, golden pubescence distributed over most body surfaces, except spines; pubescence somewhat longer and semierect at bases of spines and on propodeal dorsum.

Colour. Head, including mandibles and antennae, tips of spines and tarsi black; tibiae very dark reddish-brown; pronotal and mesonotal lateral margins narrowly bordered with black or dark brown. Mesosoma, most of petiole and coxae light to medium reddish-brown with femora darker towards distal ends. Gaster with first tergite yellowish or reddish-brown; subsequent tergites progressively darker, somewhat infuscated reddish-brown; posterior margins narrowly lined with black.

Queen
Description by Kohout (2014).

Dimensions (syntypes cited first): TL c. 10.33 – 10.58, 10.08 – 11.24; HL 2.27 – 2.34, 2.18 – 2.34; HW 1.75 – 1.81, 1.72 – 1.81; CI 77, 77 – 80; SL 3.03 – 3.22, 2.93 – 3.22; SI 173 – 178, 166 – 180; PW 2.09, 1.96 – 2.12; PeH 1.22 – 1.34, 1.18 – 1.34; PeI 52 – 59, 50-61, MTL 3.67 – 4.03, 3.63 – 4.03 (2+9 measured).

Queen larger than worker with usual characters identifying full sexuality, including three ocelli, complete thoracic structure and wings. It was described at length by Forel (1912: 73) and discussed by Kohout (1998: 508) with details not repeated here. Similarly to the worker, the queen of P. olybria closely resembles those of Polyrhachis bellicosa and Polyrhachis erosispina.