Polyrhachis lydiae

Kohout (2013): Polyrhachis lydiae is a relatively common species, frequently encountered in open eucalypt forests and savannah woodlands. They build nests in the ground with their entrances usually hidden under stones or tufts of grass. Polyrhachis lydiae ranges along the eastern Australian seaboard from about Townsville in north Queensland to just north of Newcastle in New South Wales.

Identification
A member of the schenkii species-group in the Polyrhachis subgenus Hagiomyrma. Kohout (1988): Direct comparison of the Polyrhachis schenkii holotype with lydiae syntypes (Forel coll.) shows lydiae to be a distinct and valid species. The most obvious difference is the colour, which in lydiae ranges from light metallic green to greenish or bluish black, save for the anterior part of the pronotum, which is always more or less reddish brown. P. schenkii is uniformly light reddish brown. Also, the lateral margins of the pronotal and mesonotal dorsa are more strongly converging posteriorly in schenkii than in lydiae.

Kohout (2013): Polyrhachis lydiae is a very easily recognised species due to its characteristic colour pattern. The metallic green colour is unusual and, apart from P. lydiae, occurs in only one another Australian Polyrhachis species, Polyrhachis hookeri Lowne of the subgenus Chariomyrma. However, the combination of metallic green and reddish-brown in P. lydiae is unique.

Key to Polyrhachis Hagiomyrma group species

Distribution
Known from Charters Towers in north Queensland, south to Raymond Terrace in central New South Wales.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Castes
Males and immature stages present in the QM collection.

Nomenclature

 *  lydiae. Polyrhachis schencki r. lydiae Forel, 1902h: 523 (w.q.) AUSTRALIA. Combination in P. (Hagiomyrma): Emery, 1925b: 185. Raised to species: Kohout, 1988c: 434.

Worker
Kohout (2013) - (syntypes cited first): TL c. 5.80-6.50, 5.64-6.65; HL 1.55- 1.70, 1.47-1.75; HW 1.22-1.37, 1.14-1.42; CI 79- 81, 76-83; SL 1.50-1.65, 1.50-1.78; SI 117-123, 120-134; PW 1.14-1.22, 1.00-1.25; MW 0.69-0.70, 0.59-0.78; PMI 165-174, 160-174; MTL 1.60-1.85, 1.65-2.03 (6+30 measured).

Anterior clypeal margin with obtusely denticulate, median flange. Clypeus with posteriorly elevated, median carina; distinctly sinuate in profile and rounding into well impressed basal margin. Frontal triangle poorly indicated. Frontal carinae sinuate with moderately raised margins; central area rather flat with distinct frontal furrow. Sides of head in front of eyes converging towards mandibular bases in virtually straight line; behind eyes, sides rounding into weakly convex occipital margin. Eyes convex, in full face view clearly exceeding lateral cephalic outline. Ocelli lacking. Pronotal humeri rounded with margins weakly raised anteriorly; pronotal dorsum widest near midlength; lateral margins converging into distinctly impressed promesonotal suture. Mesonotum with lateral margins converging posteriorly; metanotal groove indistinct. Propodeal margins divergent, terminating in relatively short, horizontal, acute spines, with tips curved weakly outwards. Petiole with anterior face straight, posterior face descending towards base in weakly convex line; dorsum Anterior face of first gastral tergite straight at base, widely rounding onto dorsum.

Mandibles longitudinally striate at bases, rather smooth with piliferous pits towards masticatory borders. Head, mesosoma and petiole closely reticulate-punctate. Spines weakly rugose, tips smooth and polished. Gaster very finely shagreened, polished.

Mandibular masticatory and outer borders with a few curved, golden hairs. Anterior clypeal margin with a few anteriorly directed setae medially. Whole body, including appendages, with numerous, rather short, mostly erect, bristle-like, golden hairs, somewhat longer and posteriorly directed on gaster. Appressed, rather diluted, pale golden or silvery pubescence on head and mesosoma; more abundant, somewhat longer, medially radiating golden pubescence with distinct reddish hue on dorsum of gaster; pubescence much diluted on gastral venter.

Mandibles, clypeus, condylae, sides of head at mandibular bases, outer borders of frontal carinae, anterior and lateral pronotum, appendages, including coxae, and subpetiolar process mostly light or medium reddish-brown; clypeus and central area with somewhat purplish hue. Pronotal dorsum, except anteriorly, mesosoma and petiole distinctly metallic green. Gaster medium reddish-brown.

Queen
Kohout (2013) - (syntypes cited first): TL c. 6.90-7.00, 7.21-7.51; HL 1.70-1.75, 1.65-1.75; HW 1.35, 1.29-1.35; CI 77-79, 77-79; SL 1.55-1.60, 1.55- 1.62; SI 115-119, 115-125; PW 1.50-1.55, 1.50-1.59; MTL 1.80-1.85, 1.80-1.87 (2+6 measured).

Apart from sexual characters very similar to worker, except: mesoscutum virtually as wide as long, anterior margin evenly rounded in dorsal view; relatively low with flat dorsum in lateral view; median line distinct; parapsides flat. Mesoscutellum only marginally elevated above dorsal plane of mesosoma. Propodeal spines very short, subparallel. Petiolar spines short, divergent. Sculpturation identical to worker; pilosity shorter with appressed pubescence generally more abundant. Colour scheme virtually identical to that in worker, with additional reddish-brown patches on meso- and metapleura.