Streblognathus

This southern African genus has two species, one in the southern karoo of the Eastern Cape and the other in the eastern grasslands.

Identification
Diagnosis of Streblognathus The shape of the petiolar node in the worker, with its sharp-edged dorsal margin and concave posterior face is unique among ants. The shape of the anterior margin of the clypeus is similar to that of Dinoponera in that in both genera there are lateral projections with a concave margin in between. However, the projections are acute and spine-like in Dinoponera whereas in Streblognathus they are merely obtuse points or short and tuberculate. (Robertson, 2002)

Streblognathus aethiopicus - Scape both absolutely and relatively longer (Scape length 4.32-5.11 mm; Scape index 102-113); Eye length 0.86-1.03 mm; Mesonotal-propodeal length 5.56-6.32 mm; hind tibia length 4.80-5.54 mm

Streblognathus peetersi - Scape both absolutely and relatively shorter (Scape length 3.28-4.12 mm; Scape index 87-98); Eye length 0.62-0.85 mm; Mesonotal-propodeal length 4.34-5.47 mm; Hind tibia length 3.80-4.80 mm.

Biology
Streblognathus was named by Mayr (1862) to hold a single species Streblognathus aethiopicus, originally described as Ponera aethiopica by Smith (1858). Distribution of the genus is limited to grassland and southern karoo regions of southern Africa, and it has the largest worker ants in Africa, measuring up to 2.5 cm long. Like many large southern African ponerine ants, Streblognathus  has lost the queen caste and instead, reproduction is undertaken by a single, mated worker, termed a gamergate (Ware  et al.  1990; Peeters 1991). Mandibular glands of workers contain three types of pyrazines which, in a study based on two colonies, were found to occur in smaller quantities and in different proportions in the gamergate compared with the mated workers (Jones et al. 1998). Colony size of S. aethiopicus is moderately small ranging from 9 to 51 workers (Ware et al. 1990). Workers stridulate, apparently for alarm purposes, by moving the presclerite of the second gastral segment, which has ridges on it, against the posterior edge of the first gastral segment (Lewis 1896, Ware 1994)(Robertson, 2002).

Castes
WORKER (Fig. 1). Large, black, monomorphic ants. Head (Figs 1a-c). Mandibles elongate with broad angle (about 138º) between apical and basal margin. Apical margin with three teeth followed by three denticles and with a tooth at the basal angle. Inner margin of apical tooth sinuate. Basal margin of mandible with an obtuse angle at about one third of its length from the base. The margin proximal to this angle lies adjacent to the clypeus when mandibles are closed. Mandibles glossy smooth or slightly shagreenate with sparsely distributed punctures containing hairs. Fringe of black or golden hairs inserted on dorsal surface just behind the distal two thirds of the basal margin and the basal tooth, and the hairs extending over the margin into the triangular space between the closed mandibles and the clypeal margin. Also a line of golden hairs along the external margin, and one behind the inner side of the apical margin. Maxillary and labial palps both four segmented. Margin of labrum deeply bisected and fringed with golden hairs (Fig. 1b). Anterior clypeal margin with middle section straight or concave, projecting beyond side margins and meeting them in a right angle or in a tooth-like projection (Fig. 1a). In anterior view, the region between the clypeal teeth is crescent-shaped, shiny, and overhangs the labrum (Fig. 1b). Posterior median portion of clypeus broadly inserted between the frontal lobes and indented medially. Clypeus with sparse, fine golden pubescence and smooth to shagreenate with sparsely distributed punctures containing short, black, pointed subdecumbent hairs that point anteriorly. Frontal triangle prominent between frontal carinae and inlaid into surface of head. Frontal lobes in dorsal view half obscuring the antennal sockets. Frontal carinae short, fading out just behind the level of the anterior margins of the compound eyes. Compound eyes in dorsal view situated at, or slightly anterior to, midlength of head and do not break the lateral margins. Head, excluding mandibles, rounded rectangular, usually a little longer than broad with a flat posterior margin and sides only slightly convex (Fig. 1a). Head covered in fine punctate sculpture, overlaid by fine, sparsely distributed golden pubescence, and covered by short, black, pointed, subdecumbent, curved hairs (Fig. 1c). Punctures poorly defined and unevenly distributed. Antennal scapes bowed, covered in sparse, short, golden or black subdecumbent or decumbent hairs and sparse, fine, golden pubescence. Neck between scape and condylar bulb (radicle) curved strongly downwards. Ventral surface of head smooth to shagreenate with variable densities of golden pubescence and with more-or-less evenly distributed anteriorly pointing, subdecumbent curved hairs. (Robertson, 2002)

Nomenclature

 *  STREBLOGNATHUS [Ponerinae: Ponerini]
 * Streblognathus Mayr, 1862: 716. Type-species: Ponera aethiopica, by monotypy.

Additional References

 * [[Media:Robertson 2002b.pdf| Robertson, H. G. 2002b. Revision of the ant genus Streblognathus (Hymenoptera: Formicidae: Ponerinae). Zootaxa 97: 1-16 PDF]]