Iridomyrmex discors Forel

Heterick, Brian E. & Shattuck, Steve, 2011, Revision of the ant genus Iridomyrmex (Hymenoptera: Formicidae) 2845, Zootaxa 2845 (1), pp. 1-174 : 75-76

Iridomyrmex discors Forel

( Fig. 32 )

Iridomyrmex discors Forel, 1902: 464 .

Iridomyrmex discors occipitalis Forel, 1907a: 294 (junior synonym of discors by Shattuck, 1996: 39 ).

Iridomyrmex discors occipitalis exilior Forel, 1907a: 294 (unavailable infrasubspecific name, see Taylor, 1986: 34). Iridomyrmex discors aeneogaster Wheeler, W.M., 1915a: 811 (junior synonym of discors by Shattuck, 1996: 39 ).

Types. Iridomyrmex discors Forel : Lectotype worker (here designated) from Charters Towers, Queensland, Wiederkehr (MHNG, ANIC32-009844 ). Paralectotypes, same data as lectotype (MCZC, 1 worker, examined; MHNG, 5 workers; NHMB, 1 worker). Iridomyrmex discors occipitalis Forel : Syntypes from Northampton, Western Australia (ANIC, ANIC32-009845 , 1 worker, examined; MCZC, 1 worker, examined; MHNG, 2 workers; WAMP, 1 worker). Iridomyrmex discors aeneogaster Wheeler : Holotype worker from Flat Rock Hole (as Black Rock Hole), Musgrave Ranges, South Australia (MCZC, examined). Paratypes: 1 worker, same data as holotype (ANIC, ANIC32-009848 , examined).

Worker Description. Head. Posterior margin of head weakly concave; erect setae on posterior margin in fullface 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 reddishbrown 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.

Comments. 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 I. 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 I. mayri , I. obscurior and relatives and the meat ants in the broader sense.

Meat ants do not prefer loose, sandy soils ( Greenslade, 1974), but these sorts of soils are highly suitable habitat for I. discors , which appears to be an early pioneer after soil disturbance ( Heterick, 2009). This species is a general predator/scavenger ( Shattuck, 1996 ). The first author, 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 (first author, 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.

Figures

FIGURE 32. Iridomyrmex discors (syntype, Charters Towers, Qld, ANIC32-009844): A. Front of head; B. Side of body; C. Top of body; D. Distribution of material examined (A. Noble, www.antweb.org).