Onychomyrmex mjobergi

October 24, I found two fine colonies of this species in rotten logs. One comprised at least 400 workers, a single queen, with the abdomen greatly distended with eggs, and a large number of nearly mature larvae but no pupae. The other colony was somewhat less populous but also contained many larvae. The ants moved rather slowly in long files through the cracks in the wood, evidently endeavoring to keep in close touch with one another by means of their antennae, after the manner of the Dorylinae. They stung severely for such small insects. (Wheeler 1916)

Identification
Wheeler (1916) - The worker of O. mjobergi is readily distinguished from that of Onychomyrmex hedleyi by its paler color, shorter head, antennal scapes and funicular joints, the straight dorsal profile of the thorax, broader epinotum and petiole, deeper constriction between the postpetiole and gaster, and smooth, shining, and sparsely punctate mandibles.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  mjobergi. Onychomyrmex mjobergi Forel, 1915b: 2, fig. 1; pl. 1, fig. 3 (w.) AUSTRALIA. Wheeler, W.M. 1916a: 52 (q.l.); Wheeler, G.C. & Wheeler, J. 1952c: 638 (l.).

Worker
Wheeler (1916) - Length 3.5-4 mm.

Head subrectangular, not more than i longer than broad, scarcely broader in front than behind, with feebly and evenly convex sides, feebly concave posterior border and rounded posterior corners. Clypeus with broadly arcuate anterior border, sinuate on each side, minutely and evenly denticulate. Eyes scarcely smaller than in Onychomyrmex hedleyi, situated about 2/3 the distance from the anterior to the posterior border of the head. Mandibles similar to those of hedleyi. Antennae shorter, scapes only 2/3 as long as the head, first and last funicular joints nearly twice as long as broad, remaining joints not longer than broad, the more basal joints a little broader than long. Thorax differing from that of hedleyi in being stouter and in having the dorsal outline nearly straight in profile, the pronotum being convex only at the extreme anterior end and the mesonotum less impressed. Thoracic sutures very distinct but less impressed than in hedleyi. Mesonotum fully three times as broad as long. Petiole with very short peduncle, anterior surface of node more concave, its upper surface seen from above distinctly broader than long, with very convex sides. Constriction between the postpetiole and gaster somewhat deeper than in hedleyi, legs stouter.

Smooth and shining; mandibles shining, not striate but sparsely punctate, like the remainder of the body. Punctures on the head coarser than in hedleyi, and more abundant, especially on the cheeks and sides of the front. Clypeus subopaque, rugulose-punctate.

Hairs similar to those of hedleyi but coarser and of rather uneven length, pale yellow.

Rich ferruginous red, clypeus darker; tarsal claws, sutures of thorax and gaster, articulations of antennal funiculi dark brown, mandibular teeth black; legs and anal segments of gaster paler and more yellowish.

Queen
Wheeler (1916) - Length nearly 5.5 mm.

Head a little longer than broad and nearly as broad in front as long, with prominent, depressed anterior corners, the sides converging posteriorly, with two transverse impressions, one half-way between the anterior corner and the eye and one at the eye. Eyes as small as in the worker, but more elongate. Mandibles with less abruptly incurved tips than in the worker and with only two indistinct teeth. Thorax more robust than in the worker, the pro- and epinotum with more convex sides and the pronotum more convex above, so that the mesonotum is more impressed in profile. From above the mesonotum is scarcely twice as broad as long. Petiole much larger than in the worker, with very short, slender peduncle, without ventral projection; node large, very convex in front, from above more than twice as broad as long, broader than the epinotum and nearly half as broad as the postpetiole. Gaster very much larger than in the worker, more than twice as long as broad. sub oblong, flattened dorsoventrally. Sculpture as in the worker, but the piligerous punctures, especially on the head, much coarser, almost foveolate and somewhat elongated on the sides of the front. Cheeks and sides of epinotum subopaque, finely rugulose-punctate.

Hairs coarser and longer, especially on the body, than in the worker.

Color more brownish ferruginous; mandibles, antennae, and legs more yellowish; pleurae, sides of petiole, and sutures of gaster brownish yellow.

References based on Global Ant Biodiversity Informatics

 * Brown W. L., Jr. 1960. Contributions toward a reclassification of the Formicidae. III. Tribe Amblyoponini (Hymenoptera). Bull. Mus. Comp. Zool. 122: 143-230.