Mesostruma

These uncommon ants form small colonies in soil, usually under or between rocks. They are predacious, foraging primarily on the ground in leaf litter but also occasionally on low vegetation.

Identification
The antennae are 6 segmented (including the scape). The sides of the petiole are rounded while the sides of the postpetiole are either armed with thin, wing-like flanges (best viewed from above) or are rounded.

Workers of Mesostruma are most similar to workers of Colobostruma. They differ in that Mesostruma has wing-like flanges (when present) only on the postpetiole while flanges are present on both the petiole and postpetiole in Colobostruma.

Key to Mesostruma Species

Nomenclature

 *  MESOSTRUMA [Myrmicinae: Dacetini]
 * Mesostruma Brown, 1948e: 118. Type-species: Strumigenys (Epopostruma) turneri, by original designation.
 * Mesostruma junior synonym of Colobostruma: Baroni Urbani & De Andrade, 1994: 15; Baroni Urbani & De Andrade, 2007: 94.
 * Mesostruma revived status as genus: Bolton, 1995b: 35; Bolton, 1999: 1680; Shattuck, 2000: 47.

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 elongate triangular, with a larger apical and smaller preapical tooth ; proximal of this the margin is edentate and lamellate. Mandible without an inflected basalexternal angle and not downcurved basally.

Mandibles at full gape open to only 60° - 90° ; with static pressure mode of action.

Basal process of mandible large, truncated apically, located in the same plane as the masticatory margin.

Labrum hypertrophied, forming a massive shield that can reflex tightly over the entire labio-maxillary complex and completely cover the buccal cavity; its apical margin evenly convex, not bilobate.

Trigger hairs present on dorsum of labrum.

Side of head with a vertical preocular groove, this groove not extending onto the ventral surface. Tergite of petiole without lateral lobes at the node. Tergite of postpetiole with or without lateral laminae or lobes.