Iridomyrmex discors

I. discors is commonly found in loose, sandy soils, where it appears to be an early pioneer after soil disturbance (Heterick, 2009). It is a general predator/scavenger (Shattuck, 1996). B. Heterick, as a child, often fed dead grasshoppers to I. discors workers on the footpath in front of his East Fremantle (Western Australia) house in order to examine their habits. The ants fed avidly on this prey, enlarging wounds, opening up abdomens and removing softer tissue, before finally carting the hollowed-out heads and thoraces back to their nests. As is the case with the more common meat ant species, mature nests may have multiple entrance holes (B. Heterick, pers. obs.). Iridomyrmex discors is particularly common in the Perth region in Western Australia, where it can frequently be found in sandy soils, even in street verges and between pavers in city blocks. Like its meat ant cousins it is also a pugnacious species, and workers will bite readily if the nest is threatened.

Identification
Iridomyrmex discors has a strong resemblance to a small meat ant. Probably the most salient morphological character that places it outside of the I. purpureus group is the shorter anteromedian clypeal prominence, which in full-face view does not surpass the lateral lobes of the anterior margin of the clypeus. The relative scape length is also shorter than is the case in true meat ants. Another character, suggested by Shattuck (1993a), namely a differently shaped mesonotal outline, is variable and does not in fact apply to all workers: in some cases the mesonotal outline is sinuate and arched towards its junction with the pronotum, and is thus indistinguishable from that of a meat ant. The presence of two apparently discrete populations of I. discors in Australia (Shattuck, 1996) may suggest subtle genetic distinctions, but in his revisionary treatment, Shattuck was unable to discern any significant morphological differences. Iridomyrmex discors has also been associated with Iridomyrmex obscurior, the latter being described as a subspecies of discors but raised to species by Shattuck (1996), who nonetheless considered the two species belonged to the same species-group and were in fact the only members of that group. This paper takes the view that in all likelihood the apparent similarities between the two taxa are due to convergence (the appearance of the head capsule and the anteromedian clypeal prominence is quite different in both species). Nonetheless, unpublished molecular data does suggest there could be a relatively close relationship between Iridomyrmex mayri, I. obscurior and relatives and the meat ants in the broader sense.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  discors. Iridomyrmex discors Forel, 1902h: 464 (w.) AUSTRALIA. Senior synonym of aeneogaster, occipitalis: Shattuck, 1996a: 39. See also: Heterick & Shattuck, 2011: 75.
 * aeneogaster. Iridomyrmex discors var. aeneogaster Wheeler, W.M. 1915g: 811 (w.) AUSTRALIA. Junior synonym of discors: Shattuck, 1996a: 39.
 * occipitalis. Iridomyrmex discors subsp. occipitalis Forel, 1907h: 294 (w.) AUSTRALIA. Junior synonym of discors: Shattuck, 1996a: 39.

Description
Worker Description. Head. Posterior margin of head weakly concave; erect setae on posterior margin in full- face view set in a row; sides of head noticeably convex; erect genal setae present on sides of head in full-face view. Ocelli absent; in full-face view, eyes set at about midpoint of head capsule; in profile, eye set anteriad of head capsule; eye semi-circular, or asymmetrical, curvature of inner eye margin more pronounced than that of its outer margin. Frontal carinae convex; antennal scape surpassing posterior margin of head by 1–2 x its diameter. Erect setae on scape present and abundant; prominence on anteromedial clypeal margin projecting as triangular spur; mandible elongate triangular with oblique basal margin; long, curved setae on venter of head capsule present. 'Mesosoma. 'Pronotum moderately and evenly curved over its length. Erect pronotal setae numerous (12 or more) and longest setae elongate, flexuous and/or curved. Mesonotum sinuous. Erect mesonotal setae numerous (12 or more), short and bristly. Mesothoracic spiracles always prominent as small, vertical protuberances; propodeal dorsum protuberant; placement of propodeal spiracle mesad, more than its diameter away from propodeal declivity; propodeal angle present as a bluntly defined right angle, the dorsal and declivitous propodeal faces never separated by a carina. Erect propodeal setae numerous (12 or more) and elongate, flexuous and/or curved or short and bristly. Petiole. Dorsum of node convex; node thin, scale-like, orientation more-or-less vertical. Gaster. Non-marginal erect setae of gaster present on first gastral tergite; marginal erect setae of gaster present on first tergite. General characters. Allometric differences between workers of same nest present. Colour foreparts uniformly orange to reddish- brown without iridescence in most workers (a very faint pinkish reflection may be discernible in a few cases), legs brown, gaster brown to black. Colour of erect setae pale yellow.

Measurements. Worker (n = 77)—CI 92–107; EI 20–26; EL 0.25–0.35; EW 0.15–0.23; HL 1.12–1.56; HW 1.09–1.63; ML 0.45–0.77; PpH 0.16–0.24; PpL 0.55–0.78; SI 76–100; SL 1.01–1.29.

References based on Global Ant Biodiversity Informatics

 * Andersen A. N., B. D. Hoffman, and J. Somes. 2003. Ants as indicators of minesite restoration: community recovery at one of eight rehabilitation sites in central Queensland. Ecological Management and Restoration 4: 12-19.
 * Baroni Urbani C. 1977. Katalog der Typen von Formicidae (Hymenoptera) der Sammlung des Naturhistorischen Museums Basel (2. Teil). Mitt. Entomol. Ges. Basel (n.s.) 27: 61-102.
 * Forel A. 1915. Results of Dr. E. Mjöbergs Swedish Scientific Expeditions to Australia 1910-13. 2. Ameisen. Ark. Zool. 9(16): 1-119
 * Gunawardene N. R. and J. D. Majer. 2005. The effect of fire on ant assemblages in the Gibson Desert Nature Reserve, Western Australia. Journal of Arid Environments 63: 725-739.
 * Heterick B. E., and S. Shattuck. 2011. Revision of the ant genus Iridomyrmex (Hymenoptera: Formicidae). Zootaxa 2845: 1-174.
 * Shattuck S. O. 1996. Revision of the Iridomyrmex discors species-group (Hymenoptera: Formicidae). Australian Journal of Entomology 35 :37-42.
 * Taylor R. W. 1987. A checklist of the ants of Australia, New Caledonia and New Zealand (Hymenoptera: Formicidae). CSIRO (Commonwealth Scientific and Industrial Research Organization) Division of Entomology Report 41: 1-92.