Chelaner rubriceps

Chelaner rubriceps is a very adaptable species, and can nest either in the ground or in vegetation. B. B. Lowery found a nest in a hollow twig in Ourimbah State Forest (label data). Brown (1958) comments that nests of rubriceps rubrum have been found under the loose bark of eucalyptus, and nests of rubriceps cinctum in volcanic rocks near Lake Purrumbete (Victoria). The latter were harvesting seeds. Label data also indicate that C. rubriceps may occasionally be a pest: a series from Melbourne was found damaging Telecom cable junctions (Heterick 2001).

Identification
Heterick (2001) - A member of the rubriceps group. Much of the morphological and colour variation in C. rubriceps occurs in populations from the central and northern coasts of New South Wales. South Australian and western Victorian C. rubriceps are relatively uniform in colour, and usually have a thinner petiolar node than ants from populations further east and north. A variant with a dark red or even piceous alitrunk and nodes, is more common further north; typical localities include Kingscliff, Brunswick Heads and the Myall Lakes. The Myall Lakes material is interesting in that intermediates between the light and dark C. rubriceps occur. Most Queensland material also belongs to this dark C. rubriceps variant.

Specimens with one or more yellow gastral bands have been collected from a variety of localities from the New South Wales border to as far south as Melbourne, Victoria. Ants with uniform brown or chocolate colouration have come from several centres in the Blue Mountains, west of Sydney.

Apart from colouration, there is little variation overall, though specimens within nest series often differ in size without exhibiting polymorphic traits. Significant differences between colour forms for characters such as cephalic and scape indices, or in patterns of sculpturing, have not been found. Males from Victoria, New South Wales, the Australian Capital Territory, and Norfolk Island possess a brush of setae on the third and fourth gastral sternites, and this may well prove to be a species-specific character. This feature is only lacking on a single series of three male ants from Canberra, and they exhibit other anomalies (e.g. the possession of a high petiolar node), although clearly they belong to the C. rubriceps species-complex. The species may well be adventive to Norfolk Island, having arrived there by rafting or on air currents, or (more probably) in materials transported by settlers. Brown (1958) lists C. rubriceps rubrum and C. rubriceps cinctum among ants that have been intercepted at New Zealand ports. Brown thought they probably came on imported poles.

I was unable to obtain the holotype of C. rubriceps extreminigrum. Forel distinguished this taxon from C. rubriceps on the basis of the low, thick nodes and shorter propodeal denticles. He found the taxon difficult to separate from Chelaner kiliani and Chelaner gilberti. The type worker came from Cedar Creek in Queensland. In Queensland there are several localities named “Cedar Ck”, but the only population centre is the Cedar Creek near Mount Glorious, in southeast Queensland. If this is the locality mentioned, there is no question of confusion with C. gilberti, which is found only in northeast Queensland. Moreover, the black head and red alitrunk separate this form from any of the C. kilianii or Chelaner tambourinensis populations examined, as does the presence of propodeal denticles. Nonetheless, because of the brief description, and lack of any material that can be assigned to this taxon, I consider it safer to leave the name as it stands.

Distribution
Heterick (2001) - Chelaner rubriceps is restricted to the humid east coast and to inshore and offshore islands, including Norfolk Island. On the mainland, the species can be found from the western side of Spencer's Gulf in South Australia, to Magnetic Island in North Queensland. However, few samples have been collected north of the New South Wales Queensland border, and the ant appears to be absent inland from the Great Dividing Range.

Distribution based on Regional Taxon Lists
Australasian Region: Australia, Norfolk Island.

Castes
Chelaner rubriceps shows queen polymorphism (Buschinger 2011, Tulloch 1930, Wheeler 1917). Field colonies collected and studied in NSW always yielded one egg-laying ergatoid queen. In laboratory culture such colonies produced only workers, ergatoid queens ("intermorphs") and males. After the original ergatoid queen had died, the colonies reared a few alate queens ("gynomorphs") from the remaining larvae. The species had been identified as Chelaner rubriceps by Brian Heterick (in litt.).

Nomenclature

 *  rubriceps. Monomorium rubriceps Mayr, 1876: 101 (w.m.) AUSTRALIA.
 * Emery, 1914b: 184 (q.).
 * Combination in M. (Notomyrmex): Emery, 1922e: 170.
 * Combination in Monomorium: Bolton, 1987: 284.
 * Combination in Chelaner: Ettershank, 1966: 97; Sparks et al., 2019: 233.
 * Senior synonym of cinctum, extreminigrum, rubrum, sanguinolentum: Heterick, 2001: 435.
 * rubra. Monomorium rubriceps var. rubra Forel, 1913g: 184 (w.q.m.) AUSTRALIA. [Also described as new by Forel, 1915b: 72 (footnote).] [Unresolved junior secondary homonym of rubrum Forel, above.] Subspecies of rubriceps: Taylor & Brown, D.R. 1985: 58. Junior synonym of rubriceps: Heterick, 2001: 435.
 * extreminigrum. Monomorium rubriceps r. extreminigrum Forel, 1915b: 73 (w.) AUSTRALIA. Combination in Chelaner: Ettershank, 1966: 96; in Monomorium: Taylor, 1987b: 3. Junior synonym of rubriceps: Heterick, 2001: 435.
 * cinctum. Monomorium rubriceps var. cinctum Wheeler, W.M. 1917b: 113, fig. 3 (w.q.) AUSTRALIA. Combination in Chelaner: Ettershank, 1966: 96; in Monomorium: Taylor, 1987b: 3. Subspecies of rubriceps: Taylor & Brown, D.R. 1985: 58. Junior synonym of rubriceps: Heterick, 2001: 435.
 * sanguinolentum. Monomorium (Notomyrmex) sanguinolentum Wheeler, W.M. 1927i: 135, fig. 4 (w.m.) AUSTRALIA. Combination in Chelaner: Ettershank, 1966: 97; in Monomorium: Bolton, 1987: 284. Junior synonym of rubriceps: Heterick, 2001: 435.

Worker
Heterick (2001) - HML 2.72-3.81; HL 0.91-1.24; HW 0.77-1.15; CeI 86-96; SL 0.64-0.96; SI 72-88; PW 0.51-0.75 (26 measured).

Head. Head square or rectangular, or rounded; vertex slightly concave to planar; frons smooth and shining with combination of appressed setulae and erect and suberect setae, or smooth and shining with combination of incurved decumbent and subdecumbent setulae and erect and suberect setae. Compound eyes elliptical; (viewed from front) compound eyes set in anterior half of head capsule; (viewed laterally) compound eyes set at midline of head capsule; eye moderate, eye width 0.5-l.Sx greatest width of antennal scape. Antennal segments 12; club three-segmented. Anteromedial clypeal margin emarginate, median clypeal carinae indistinct. Longest lateral anterior clypeal setae long, extending beyond dorsal margin of closed mandibles. Posteromedial clypeal margin level with posterior surface of antennal fossae. Anterior tentorial pits situated nearer antennal fossae than mandibular insertions. Frontal lobes parallel straight. Venter of head capsule without elongate, basket-shaped setae. Palp formula 2,3. Maximum number of mandibular teeth and denticles: five; mandibles (viewed from front) triangular and striate, with piliferous punctures, or strap-like with inner and outer edges subparallel, striate, with piliferous punctures; basal tooth not enlarged; basal angle indistinct; apical and basal mandibular margins meeting in tooth or denticle.

Alitrunk. Promesonotal sculpture present in form of microreticulation and striolae on and around katepisternum, otherwise promesonotum smooth and shining; dorsal promesonotal face evenly convex; erect and suberect promesonotal setae greater than 10; setulae appressed, or decumbent and subdecumbent. Mesonotal suture absent. Metanotal groove present as feebly impressed furrow between promesonotum and propodeum to present as distinct and deeply impressed trough between promesonotum and propodeum. Propodeal sculpture present as faint microreticulation with few striae, mainly on lower lateral surface; dorsal propodeal face flattened to sloping posteriad, with wedge-shaped flattening or shallow depression that is widest between propodeal angles; processes absent (propodeum smoothly rounded in profile or with slight hump at propodeal angle), or absent (propodeum angulate in profile), or present on posterior propodeal angles as small denticles or sharp flanges; lobes present as blunt flanges. Propodeal angle absent, or present; declivitous face of propodeum flat to longitudinally concave between its lateral margins. Erect and suberect propodeal setae >5 to 5-10; propodeal setulae decumbent and subdecumbent. Propodeal spiracle lateral and about midway between metanotal groove and declivitous face of propodeum; vestibule conspicuous through cuticle.

Petiole and postpetiole. Petiolar spiracle lateral and in anterior sector of petiolar node. Petiolar node conical, dorsally rounded, or cuneate, dorsally rounded; sculpture absent, petiolar node smooth and shining. Ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) near 4:3. Anteroventral process distinct in some individuals as slender carina that tapers posteriad. Ventral lobe always absent. Height ratio of petiole to postpetiole near 1:1; height-length ratio of postpetiole near 2:1 to near 1:1. Sculpture absent on dorsum, at least: postpetiole smooth and shining. Ventral process present and distinct.

Gaster. Pilosity of first gastral tergite consisting of combination of appressed setulae and longer, erect and suberect setae.

General characters. Extremely variable in colour, even within nest series: typical or distinctive morphs include the following: (1) Monomorium rubriceps cinctum, head brown, or brown with areas of orange on frons and around mandibles, mandibles, alitrunk, petiole and postpetiole tawny orange, gaster bright yellow basaly, rest of gaster with one or more transverse dark brown bands; (2) M. rubriceps rubrum, as for (1), but with a bright orange head and alitrunk; (3) Monomorium sanguinolentum, as for 1, but with head darker, and gaster without a yellow basal region or lighter bands; (4) a colour morph with head tawny yellow, alitrunk, petiole, postpetiole and appendages dark brown or chocolate; (5) morph as for (4) but with anterior promesonotum yellowish orange; (6) a series from the Australian Capital Territory, head dark chocolate, alitrunk, petiole and postpetiole gamboge, gaster as for (1), appendages dark brown: there are many other colour patterns that interconnect with these more distinctive morphs. Worker caste monomorphic but variable in size, with series of intercastes between largest and smallest workers (monophasic allometry).

Queen
Heterick (2001) - HML 4.29-5.38; HL 1.29-1.60; HW 1.29-1.60; CeI 96-107; SL 0.83-1.09; SI 64-73; PW 0.93-1.26 (9 measured).

Head. Head rounded; vertex slightly concave; frons striolate with decumbent and subdecumbent setulae of variable lengths. Compound eyes circular or subcircular; (viewed from front) compound eyes set in anterior half of head capsule; (viewed laterally) compound eyes set at midline of head capsule; eye large, eye width greater than 1.5 x greatest width of antennal scape.

Alitrunk. Mesoscutum in profile evenly flattened. Mesoscutal pilosity consisting of decumbent and subdecumbent setulae anteriad and erect and suberect setae posteriad; dorsal appearance of mesoscutum smooth and shining; length-width ratio of mesoscutum and scutellum combined near 2:1 to near 4:3. Axillae separated by distance less than half greatest width of scutellum. Propodeal sculpture present as uniform rugosity, with well defined costulae on declivitous face of propodeum; dorsal propodeal face flattened. Propodeal processes present on posterior propodeal angles as small denticles or sharp flanges; lobes present as blunt flanges. Propodeal angle present. Erect and suberect propodeal setae 5-1 0; propodeal setulae decumbent and subdecumbent. Propodeal spiracle lateral and nearer metanotal groove than declivitous face of propodeum, or lateral and about midway between metanotal groove and declivitous face of propodeum.

Wing. Wing veins tubular and strongly sclerotised; vein m-cu present as an entire vein enclosing first discoidal cell; vein cu-a present.

Petiole and postpetiole. Petiolar spiracle lateral and in anterior sector of petiolar node. Petiolar node cuneate, dorsally rounded, or tumular and inclined posteriad; sculpture absent, petiolar node smooth and shining. Ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) near 2:1 to near 4:3. Anteroventral process always absent or vestigial. Height ratio of petiole to postpetiole near 1:1; height-length ratio of postpetiole near 2:1 to near 4:3. Sculpture absent on dorsum, at least: postpetiole smooth and shining; ventral process present and distinct.

Gaster. Pilosity of first gastral tergite consisting of combination of appressed setulae and longer, erect and suberect setae.

General characters. Colour generally reddish-orange with two or more brown gastral bands; in other examples alitrunk, petiole and postpetiole partly or wholly infuscated with brown or black. Brachypterous alates not seen. Ergatoid or worker-female intercastes seen and examined.

Male
Heterick (2001) - HML 2.90-3.62; HL 0.83-0.98; HW 0.85-1.06; CeI 95-108; SL 0.28-0.39; SI 30-42; PW 0.88-1.09 (11 measured).

Head. Head width-mesoscutal width ratio near 1:1. Compound eyes protuberant and elliptical; (viewed laterally) compound eyes set posterior of the midline of head capsule; ocelli not turreted. Ratio of length of first funicular segment of antenna to length of second funicular segment near 2:5 to near 1:2. Maximum number of mandibular teeth and denticles: four.

Alitrunk. Mesoscutum in profile evenly flattened; dorsal appearance of mesoscutum finely microreticulate; mesoscutal pilosity consisting of long, dense setae. Parapsidal furrows present and distinct; notauli present. Axillae separated by distance more than half greatest width of scutellum.

Wing. Wing veins tubular and strongly sclerotised; vein m-cu present as an appendix, or present as an entire vein enclosing first discoidal cell; vein cu-a present.

Petiole and postpetiole. Petiolar spiracle lateral and in anterior sector of petiolar node, or lateral and slightly anteriad of petiolar node. Sculpture absent, petiolar node smooth and shining; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) near 3:4. Anteroventral process always absent or vestigial; ventral lobe always absent. Height-length ratio of postpetiole near 4:3; sculpture absent on dorsum, at least: postpetiole smooth and shining; ventral process absent or vestigial.

Gaster. Pilosity of first gastral tergite consisting of combination of appressed setulae and longer, erect and suberect setae.

General characters. Colour brown to chocolate.