Monomorium stictonotum

Abundant in many arid and semi-arid habitats, this ant has been found in mallee, various vegetation types that are quite open (heathland, shrub, etc.) and dunes.

Identification
Heterick (2001) - A member of the monomorium group. Monomorium stictonotum is only weakly distinguished from Monomorium aithoderum, and may eventually prove to be a variant of the latter species. The conformation of the eye is the only feature by which the two species can be separated. As presently recognised, this ant has a fairly wide distribution, mainly in the arid and semi-arid regions of South Australia and Western Australia. Despite its abundance, the worker caste of M. stictonotum is the only caste that can be identified.

Monomorium stictonotum is fairly uniform in colour and morphological features throughout its range, but the series from Kukerin, Western Australia, differ from other collections in that the workers have stout, erect setae on the alitrunk and vertex. Other workers have mainly appressed setulae on the alitrunk and vertex, but one specimen from the Olympic Dam site, South Australia, has a few small erect setae on the promesonotum.

This species may also be confused with Monomorium nanum, but can be distinguished its humped and more elongate promesonotum, and the greater distance between the eye and the mandibular insertion.

Heterick (2009) - Monomorium aithoderum, Monomorium nanum and Monomorium stictonotum are minute, nondescript orange or brownish species of very similar appearance that make up much of the Monomorium biomass in drier areas of southern Australia.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  stictonotum. Monomorium stictonotum Heterick, 2001: 415, figs. 32, 124, 142 (w.) AUSTRALIA.

Worker
Holotype. HML 1.36; HL 0.54; HW 0.45; Cel 83; SL 0.45; SI 100; PW 0.28. Others. HML 1.11-1.4 7; HL 0.46-0.58; HW 0.36-0.49; CeI 80-90; SL 0.34-0.46; SI 88-100; PW 0.18-0.25 (17 measured).

As for the worker of Monomorium sydneyense, but with the following apomorphies.

Head. Vertex of head capsule planar; frons smooth and shining with evenly spaced, appressed setulae, or smooth and shining with combination of appressed setulae and erect and suberect setae. Compound eyes reniform, with posterior surface of eye emarginate; (viewed from front) compound eyes set in anterior half of head capsule, or set at midpoint of each side of head. Eye large, eye width greater than 1.5x greatest width of antennal scape. Anteromedial clypeal margin emarginate, median clypeal carinae produced apically as pair of pronounced teeth, or emarginate, median clypeal carinae produced as pair of bluntly rounded denticles. Venter of head capsule with elongate, basket-shaped setae in at least some individuals. Maximum number of mandibular teeth and denticles: three; mandibles (viewed from front) strap-like with inner and outer edges subparallel, smooth with piliferous punctures.

Alitrunk. Promesonotal sculpture present in form of uniform microreticulation with few mesopleural striolae (or with microreticulation confined to posterior promesonotum only; anterior promesonotum smooth and shining); dorsal promesonotal face evenly convex. Propodeal sculpture present as uniform microreticulation, with few or no striae or costulae. Declivitous face of propodeum flat. Erect and suberect propodeal setae absent or very sparse, or 5-10.

Petiole and postpetiole. Ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) near 4:3 to near 1:1. Ventral lobe always absent. Height ratio of petiole to postpetiole near 4:3.

Gaster. Pilosity of first gastral tergite consisting entirely of well-spaced appressed setulae.

General characters. Colour pale brown to chocolate, mandibles yellow. Gaster may be darker than alitrunk. Worker caste monomorphic.

Etymology
Greek: “punctate + back”.

References based on Global Ant Biodiversity Informatics

 * CSIRO Collection
 * Heterick B. E. 2001. Revision of the Australian ants of the genus Monomorium (Hymenoptera: Formicidae). Invertebrate Taxonomy 15: 353-459.