Epopostruma

An Australian genus, Epopostruma workers can be fairly common but are often overlooked. Workers are slow-moving and most lie motionless when disturbed. Their nests are small, with up to about 100 workers, and are found in open soil or in soil under rocks, logs or small sticks. They also nest in cracks in large rocks. When nesting in open soil they are often found near the bases of trees.

Identification
The antennae are 6 segmented (including the scape) and the scapes pass below the eyes when laid back against the head in their normal resting position. The mandibles are thin and elongate and when fully closed they are separated by a broad gap for most of their length, touching only at the tips. These characters will separate Epopostruma from all other Australian ants, including the superficially similar Colobostruma, Eurhopalothrix, Mesostruma and Rhopalothrix.

Key to Epopostruma Species

Biology
Almost all species forage at night although one species is known to occasionally forage on mallee stems during the day. They are also regularly found in leaf litter. Workers have been attracted to honey baits on trees in the late evening and at night. Their elongate and specialised mandibles form a type of snap-trap which is used to captured soft-bodied prey such as Collembola.

Nomenclature

 *  EPOPOSTRUMA [Myrmicinae: Dacetini]
 * Epopostruma Forel, 1895f: 422 [as subgenus of Strumigenys]. Type-species: Strumigenys (Epopostruma) quadrispinosa, by subsequent designation of Wheeler, W.M. 1911f: 163.
 * Epopostruma raised to genus: Emery, 1897c: 573.
 * Epopostruma senior synonym of Hexadaceton: Taylor & Brown, D.R. 1985: 63; Bolton, 1999: 1681; Shattuck, 2000: 53.
 * Epopostruma senior synonym of Colobostruma, Mesostruma: Baroni Urbani & De Andrade, 2007: 94.
 * HEXADACETON [junior synonym of Epopostruma]
 * Hexadaceton Brown, 1948e: 120. Type-species: Hexadaceton frosti, by original designation.
 * Hexadaceton junior synonym of Epopostruma: Taylor & Brown, D.R. 1985: 63; Bolton, 1999: 1681; Shattuck, 2000: 53.

Worker
Shattuck (2000):

With characters of the epopostrumiform genus group......

Palp formula 5, 3.

Labrum large or very large, forming a massive shield in Colobostruma and Mesostruma that can reflex tightly over the labio-maxillary complex and completely cover the buccal cavity; somewhat smaller in Epopostruma where it covers approximately the apical half of the labio-maxillary complex.

Basimandibular gland bulla absent.

Antenna usually with 4 - 6 segments, rarely more.

Scape, when laid back in its normal resting position, passes below the eye or across the ventral margin of the eye; basal part of scape strongly downcurved.

Scrobe usually present, extending below the eye, the latter not located ventrolaterally on side of head.

Femora and tibiae lack gland bullae on their dorsal surfaces.

Pronotal humeri usually armed.

Metapleural gland with apex of bulla close to or abutting the annulus of the propodeal spiracle.

Propodeal spiracle at about the m idheight of the sclerite, separated from margin of declivity.

Tergite of petiole or postpetiole with lateral cuticular laminar outgrowths; extremely rarely (1 species) with traces of spongiform tissue.

Postpetiolar spiracles ventral.

Limbus absent from first gastral tergite.

Suture separating first gastral tergite and stemite angulate laterobasally; horizontal basal margin of stemite with a raised rim or crest adjacent to the tergite margin, this crest usually continues round the laterobasal angle.

Bizarre pilosity never developed.

......and the following.....

Mandibles linear, with kinetic mode of action, edentate except for two enlarged teeth apically that overlap at full closure; in ventral view without an inflected basalexternal angle.

Mandibles at full gape open to 170° or more.

Basal process of mandible a curved truncated bar.

Labrum covers approximately the apical half of the labio-maxillary complex, its anterior margin not evenly convex; side of labrum with a small rectangular process.

Labrum mediodorsally with a very broadly and deeply concave depression in its proximal half.

Trigger hairs two in number, long and stout, arising from labrum and widely separated.

Side of head with a vertical preocular groove that may extend onto the ventral surface.

Scrobe strongly present, extending below eye.