Chelaner bicornis

The Western Australian Department of Agriculture has workers of this species, which are said to have caused the death of poultry in southwestern country areas. The close resemblance of C. bicorne to Chelaner whitei suggests that this species is also largely or wholly graminivorous. (Heterick 2001)

Identification
Heterick (2009) - A member of the bicorne group. A dark brown to black-and-yellow species. East coast workers are essentially dark brown, black or black-and-brown. Workers in the SWBP, WA are black with yellow gasters.

Distribution
Heterick (2009) - Found throughout temperate Australia.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  bicorne. Monomorium bicorne Forel, 1907h: 276 (q.) AUSTRALIA.
 * Heterick, 2001: 370 (w.m.).
 * Combination in M. (Notomyrmex): Emery, 1922e: 170.
 * Combination in Monomorium: Taylor, 1987b: 2.
 * Combination in Chelaner: Ettershank, 1966: 96; Sparks et al., 2019: 232.
 * Senior synonym of macareaveyi: Heterick, 2001: 370.
 * niger. Monomorium (Holcomyrmex) niger McAreavey, 1949: 12, figs. 36-41 (w.q.m.) AUSTRALIA. [Junior secondary homonym of Holcomyrmex criniceps var. niger Forel, above.] Replacement name: Monomorium macareaveyi Ettershank, 1966: 97.
 * macareaveyi. Chelaner macareaveyi Ettershank, 1966: 97. Replacement name for Monomorium niger McAreavey, 1949: 12. [Junior secondary homonym of Holcomyrmex criniceps var. niger Forel, 1902c: 220.] Combination in Monomorium: Taylor, 1987b: 3. Junior synonym of bicorne: Heterick, 2001: 370.

Heterick (2001) - The holotype of this species was collected at Gooseberry Hill, in the Darling Ranges, Western Australia. The assigning of Western Australian worker material to C. bicorne is necessarily tentative, as the holotype, an apparently dealate queen, appears to have been destroyed. Furthermore, no drawing accompanies Forel's description. An old pin with three workers collected from Tammin by J. Clark has a label bearing the name C. bicorne, but it is not known whether Clark was responsible for the label. Nonetheless, the characteristics particularly noted by Forel, namely the clypeal teeth and the colouration, are consistent with the appearance of the worker specimens mentioned above. The general description and the dimensions also agree with putative C. bicorne, and are unlikely to refer to any other southwestern Australian Chelaner, except Chelaner whitei. C. whitei, though, normally occurs in arid and semi-arid areas well inland from the coast.

Eastern Australian material referable to Chelaner macareaveyi is identical to C. bicorne in all respects except for the colour of the gaster (chocolate to light brown compared with bright orange or gamboge in most specimens). However, some ants from the Fleurieu Peninsula in South Australia, as well as Tardun in Western Australia, are intermediate in colouration. Therefore, there appears to be no reason to maintain two distinct taxa, especially as many other Australian Chelaner are highly variable in colour. Since extant material is referred to C. bicorne on the basis of a description without figures and on some circumstantial evidence, no neotype has been assigned.

Worker
Heterick (2001) - HML 2.74-4.26; HL 1.04-1.72; HW 1.04-1.68; Cel 91-106; SL 0.61-1.09; SI 59-69; PW 0.51-0.88 (50 measured).

Head. Head square or rectangular; vertex slightly concave; frons smooth and shining with combination of appressed setulae and erect and suberect setae, or microreticulate and striolate with combination of appressed setulae and erect and suberect setae, or longitudinally striate with erect and suberect setae. Compound eyes ovoid; (viewed from front) compound eyes set in anterior half of head capsule; (viewed laterally) compound eyes set anterior of midline of head capsule; eye moderate, eye width 0.5-1.5 x greatest width of antennal scape to large, eye width greater than 1.5 x greatest width of antennal scape. Antennal segments 12; club gradually tapering and barely discernible. Anteromedial clypeal margin emarginate, median clypeal carinae produced apically as pair of pronounced teeth, with an additional tooth or denticle on either side. Longest lateral anterior clypeal setae long, extending beyond dorsal margin of closed mandibles. Posteromedial clypeal margin situated between anterior and posterior surfaces 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: four; mandibles (viewed from front) strap-like with inner and outer edges subparallel, smooth with piliferous punctures; basal tooth not enlarged; basal angle indistinct; apical and basal mandibular margins meeting in curve.

Alitrunk. Promesonotal sculpture present in form of uniform microreticulation with few mesopleural striolae; dorsal promesonotal face evenly convex; erect and suberect promesonotal setae greater than 10; setulae appressed. Mesonotal suture visible externally as faint ridge. Metanotal groove present as distinct and deeply impressed trough between promesonotum and propodeum. Propodeal sculpture present as uniform rugosity, with well defined costulae on declivitous face of propodeum; dorsal propodeal face 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); lobes present as blunt flanges. Propodeal angle absent, or present; length ratio of dorsal face to declivitous face near 2:1, or not applicable; declivitous face of propodeum flat. Erect and suberect propodeal setae >5; propodeal setulae appressed. Propodeal spiracle lateral and about midway between metanotal groove and declivitous face ofpropodeum; vestibule conspicuous through cuticle.

Petiole and postpetiole. Petiolar spiracle lateral and slightly anteriad of petiolar node. Petiolar node tumular and inclined posteriad; sculpture present in form of microreticulation, or present; petiolar node rugose. Ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) near 4:3 to near 1:1. Anteroventral process present as pronounced spur, or slender carina that tapers posteriad. Ventral lobe always absent. Height ratio of petiole to postpetiole near 4:3; height-length ratio of postpetiole near 4:3 to near 1: 1. Sculpture present in form of microreticulation or rugosity. 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 dark brown to black, gaster reddish orange through to black. Worker caste monomorphic but variable in size, with series of intercastes between largest and smallest workers (monophasic allometry).

Queen
Heterick (2001) - HML 4.37-4.73; HL 1.21-1.37; HW 1.35-1.50; Cei 108-116; SL 0.88-0.98; SI 61-70; PW 1.03-1.35 (7 measured).

Head. Head square or rectangular; vertex planar; frons longitudinally striate 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 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 longitudinally striate; length-width ratio of mesoscutum and scutellum combined 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 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. Erect and suberect propodeal setae greater than 10; propodeal setulae decumbent and subdecumbent. Propodeal spiracle 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 slightly anteriad ofpetiolar node, or lateral and positioned in pedicel well anteriad of petiolar node. Petiolar node cuneate, dorsally rounded; sculpture present in form of microreticulation, or present; petiolar node rugose. Ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) near 1:1. Anteroventral process always absent or vestigial. Height ratio of petiole to postpetiole near 1: 1 to near 4:3; height-length ratio of postpetiole near 4:3. Sculpture present in form of microreticulation; 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 of head, alitrunk, petiole and postpetiole dark chocolate to black; appendages brown; gaster tawny yellow to black; appendages brown. Brachypterous alates not seen. Ergatoid or worker-female intercastes not seen.

Male
Heterick (2001) - HML 3.29-5.02; HL 0.78-1.14; HW 0.83-1.29; Cel 103-114; SL 0.21-0.31; Sl 20-30; PW 0.83-1.32 (5 measured).

Head width-mesoscutal width ratio near 3:4. Compound eyes protuberant and elliptical; (viewed laterally) compound eyes set at midline of head capsule; ocelli not turreted. Ratio of length of first funicular segment of antenna to length of second funicular segment near 1:3 to near 1:4. Maximum number of mandibular teeth and denticles: three.

Alitrunk. Mesoscutum in profile convex anteriad; thereafter flattened; dorsal appearance of meso scutum finely microreticulate; mesoscutal pilosity consisting of numerous short setae, incurved medially. Parapsidal furrows present and distinct; notauli absent. Axillae separated by distance of about half greatest width of scutellum.

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

Petiole and postpetiole. Petiolar spiracle lateral and positioned in pedicel well anteriad of petiolar node. Sculpture present in form of microreticulation; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) near 3:4. Anteroventral process distinct in some individuals as slender carina that tapers posteriad; ventral lobe always absent. Height-length ratio of postpetiole near 4:3 to near 1: 1; sculpture present in form of microreticulation; ventral process absent or vestigial.

Gaster. Pilosity of first gastral tergite consisting entirely of well-spaced appressed setulae.

General characters. Colour black; gaster amber; legs dark chocolate.