Leptomyrmex cnemidatus

L. cnemidatus has been recorded in wet sclerophyll, dry sclerophyll, rainforest and semi-evergreen vine thicket. Nests occur in or under rocks and logs, or in holes in the ground.

Identification
Throughout the major part of its range in northeastern New South Wales and southeastern Queensland, Leptomyrmex cnemidatus can be distinguished from congeners by the combination of head shape (elongate, with rounded postocular margin and long scapes: CI 0.59–0.63; SI 2.94–3.12), coloration (orange, with gaster and distal portions of the femora black) and size (HW 1.20–1.39 mm; WL 3.79–4.32 mm). These characters separate it from sympatric species with which it might be confused, including Leptomyrmex nigriventris (considerably larger: HW 1.49–1.76 mm; WL 4.32–4.98 mm; legs unicolorous orange), Leptomyrmex rothneyi (postocular margin of head con¬stricted and projecting; head and pronotum spotted or mottled), Leptomyrmex rufipes (postocular margin of head con¬stricted and projecting), Leptomyrmex tibialis (considerably larger and head broader: HW 1.68–1.96 mm; WL 4.51–5.13 mm; CI 0.71–0.79), Leptomyrmex varians (legs, including coxae, black) and L. wiburdi (head broad, scapes shorter: CI 0.66–0.70; SI 2.29–2.64).

In some portions of its range, L. cnemidatus can be difficult to distinguish from its sister species, Leptomyrmex erythrocephalus. In the Blue Mountains these species maintain morphological and color differences in sympatry, and north of Sydney L. cnemidatus occurs within 100km of the coast whereas L. erythrocephalus is found in inland, more than 100km from the coast. In the Sydney region, however, L. cnemidatus becomes variable in coloration and can be difficult to distinguish from its sister species. This area of confusion may represent a recent contact zone where the two species are introgressing, or it may be that in this region complete divergence has never occurred. Study of this scenario on the population level will be needed to gain insight into the status of these two species in this area. In general, L. cnemidatus is the smaller of the two species, and can be identified by the presence of 2–4 black setae on the clypeus (L. erythrocephalus has 0–2 black setae). If only 2 setae are present, then these are separated by less than 0.25 mm, whereas L. erythrocephalus possesses 0-2 setae and the hairs are separated by more than 0.25mm.

Key to Australian Leptomyrmex Species

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  cnemidatus. Leptomyrmex erythrocephalus var. cnemidatus Wheeler, W.M. 1915d: 268 (w.) AUSTRALIA. Wheeler, W.M. 1934c: 92 (m.). Subspecies of erythrocephalus: Wheeler, W.M. 1934c: 92. Raised to species: Lucky & Ward, 2010: 26. Senior synonym of brunneiceps, venustus: Lucky & Ward, 2010: 26.
 * brunneiceps. Leptomyrmex erythrocephalus subsp. brunneiceps Wheeler, W.M. 1934c: 88 (w.) AUSTRALIA. Junior synonym of cnemidatus: Lucky & Ward, 2010: 26.
 * venustus. Leptomyrmex erythrocephalus subsp. venustus Wheeler, W.M. 1934c: 87, fig. 5 (w., ergatoid q.) AUSTRALIA. Junior synonym of cnemidatus: Lucky & Ward, 2010: 26.

Description
Lucky and Ward (2010):

Worker
measurements (n = 9) HL 1.99–2.29, HW 1.20–1.39, MFC 0.23–0.30, IOD 0.68–0.80, SL 3.64–4.18, EL 0.40–0.48, WL 3.79–4.32, PW 1.07–1.25, DPW 0.37–0.50, HTL 4.44–5.08, HTWmin 0.12–0.17, HTWmax 0.27–0.31, CI 0.59–0.63, SI 2.94–3.12, OI 0.10–0.14, HTC 0.41–0.60.

Medium to small species (HW 1.20–1.39 mm; WL 3.79–4.32 mm) with head, excluding mandibles, less than twice as long as broad (CI 0.59–0.63). Head widest at eye level, sides of head subparallel, narrowing anteriorly, genae straight. Head posterior to eyes rounding and gently narrowing to flat posterior margin. Mas¬ticatory margin of mandible with approximately 7 teeth and 15 denticles interspersed. Anterior clypeal margin weakly concave medially. Eyes positioned approximately at midline of head, relatively small and hairless, reaching but not surpassing lateral margin of head. Antennae not compressed, scapes surpassing the posterior margin of head by about 3/5 of their length. Pronotum long and slender. Propodeal declivity about 1/3 as long as dorsal face, the latter bearing a transverse impression at anterior end. Propodeal angle rounded. Petiole in profile slightly bulbous, median longitudinal impression on anterior, dorsal and posterior faces. Posterior face of petiole concave, ventral face convex. Gaster elliptical. Femora and tibiae compressed. Whole body, includ¬ing mandibles, subopaque, finely and densely shagreened. Mandibles with a row of coarse punctures along margin. Short, whitish pubescence covering surface, lending pruinose appearance. Pilosity confined to mandi¬bles and clypeus and venter. Ventral face of fore, mid and hind tibia with irregular row of short dark bristles.

Typical color pattern consisting of rufotestaceous head and mesosoma, with gaster and distal portions of femora black. Variation from this color pattern is common; in the area of sympatry with Leptomyrmex erythrocephalus (Sydney region) the central portion of clypeus, excluding the anterior margin, presents 2–4 black setae (sometimes abraded—look for black setal base); if only 2 setae are present, these are separated by less than 0.25 mm.

Queen
Head broader than in worker, the posterior border slightly impressed medially. Three ocelli deeply set into head in triangular formation, the anteriormost one largest, the posterior two smaller. Anterior clypeal margin nearly flat. Pronotum, mesonotum and propodeum voluminous, convex. Dorsal face of propodeum convex, thus lacking transverse impression. Petiole broader than high, with distinct medial impression. Gaster glo¬bose, larger than in worker. Scapes, femora and tibiae broad, robust.

Surface of body dull and opaque, appearing dusty. Pilosity longer on the clypeus; pubescence on gaster longer and yellowish. Queen coloration similar to that of worker.

Male
measurements (n = 5) HL 1.37–1.55, HW 1.02–1.11, SL 0.44–0.50, EL 0.55–0.68, HTL 3.84–4.34, CI 0.70–0.78, SI 0.42–0.45, SI2 0.91–1.02.