Iridomyrmex suchieri

Iridomyrmex suchieri is arguably one of the most significant Iridomyrmex species. Populations are found in all Australian states, and the ant is a minor peridomestic nuisance in New Zealand, where it has become established in the North Island, in Nelson in the South Island and on some offshore islands (Don, 2007).

In Australia, I. suchieri is quite anthropophilic and can be found in most capital cities, where it occurs on pavements as well as in vegetated areas. Paving stones are a favoured form of cover, and, although nests are not especially large, quite a lot of sand can be removed. In more natural surroundings, stones may also be used for nest protection. label data detailing behaviour of this species in Australia is almost completely lacking, but in New Zealand it follows typical Iridomyrmex behaviour in tending honeydew producing Hemiptera (Don, 2007). There is a strong likelihood that Australian workers of this species also tend lycaenid caterpillars, but such data are treated with caution by Eastwood and Fraser (1999) because of the uncertainty surrounding the taxonomy of Iridomyrmex species to this point of time.

Identification
As with most of the other small and small-medium Iridomyrmex, the species has no notable features. The combination of a more-or-less flattened propodeum with a distinct propodeal angle and a line of short, erect setae on the posterior margin of the head are the best ways of identifying this ant. In general, most populations of I. suchieri have glabrous antennal scapes and hind tibiae and lack erect setae on the sides of the head capsule. This form is represented by the two syntype workers of I. suchieri from Dongara. Occasional workers have hairy tibiae. In these specimens, previously treated as belonging to Iridomyrmex obscurus, the antennal scape may remain glabrous, or possess small, fine, erect and semi-erect setae, which may be evenly distributed along the scape or be concentrated towards the end of the scape. Iridomyrmex suchieroides is a very similar ant, but, whereas hairy populations of I. suchieri may have erect setae on the hind tibiae and the antennae (as stated above), even the hairiest I. suchieroides always have glabrous antennae and lack erect setae on the hind tibia. In addition, many populations of less hairy I. suchieri lack erect setae on the sides of their head capsules (except near the mandibles), whereas such setae are always present in I. suchieroides. The latter also has a slightly differently shaped propodeum that is narrower and more rounded.

Iridomyrmex obscurus represents no more than the hairier form of I. suchieri, where erect setae are variously present on the antennal scapes, legs and/or sides of head. However, this hairiness is part of the natural variation in I. suchieri, and many specimens have varying degrees of such hairiness, often with only one or two erect setae on the antennal scapes, or the sides of the head lacking in such vestiture although the hind tibiae are hairy, or other combinations involving these structures. In fact, in a paratype series (two workers) of I. obscurus with the same collection data as the syntypes of I. obscurus, the hairy tibiae and sides of head contrast with the glabrous scape. Iridomyrmex obscurus is therefore treated as a junior synonym of I. suchieri (the earlier name).

Some populations of Iridomyrmex mjobergi are also identical in appearance to I. suchieri, but are virtually glabrous, and lack the setae on the posterior margin of the head mentioned above. Unfortunately, I. suchieri is variable is size and shape, and small workers may have a more rounded propodeum than their more typical counterparts. In these cases, care must be taken to avoid confusion with Iridomyrmex splendens. The latter nearly always has some iridescence on the body (absent or confined to the gaster in I. suchieri), and a planar or weakly medially indented posterior margin of the head (uniformly weakly concave in I. suchieri).

Distribution based on Regional Taxon Lists
Australasian Region: Australia, New Zealand, Norfolk Island.

Nomenclature

 *  suchieri.  Iridomyrmex rufoniger subsp. suchieri Forel, 1907h: 291 (w.q.m.) AUSTRALIA. Raised to species: Heterick & Shattuck, 2011: 144. Senior synonym of obscurus Heterick & Shattuck, 2011: 144.
 * obscurus. Iridomyrmex obscurus Crawley, 1921: 92, fig. 1 (w.) AUSTRALIA. Junior synonym of suchieri Heterick & Shattuck, 2011: 144.

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, or absent from sides of head in full-face view (one to a few small setae may be present near mandibular insertion). Ocelli absent; in full-face view, eyes set above midpoint of head capsule; in profile, eye set anteriad of head capsule; eye 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 sparse, or absent, except at tip; prominence on anteromedial clypeal margin projecting as blunt but distinct protuberance; mandible regularly triangular with oblique basal margin; long, curved setae on venter of head capsule absent. Mesosoma. Pronotum moderately and evenly curved over its length. Erect pronotal setae moderate in number (6– 12), longest setae elongate, flexuous and/or curved, or sparse (6 or fewer) and bristly. Mesonotum straight. Erect mesonotal setae moderate in number (6– 12), short and bristly, or sparse (6 or fewer) and bristly. Mesothoracic spiracles always inconspicuous; propodeal dorsum straight and short (equal in length to propodeal declivity); placement of propodeal spiracle posteriad and near propodeal declivity, or 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, or weakly present or absent, the confluence of the dorsal and declivitous propodeal faces indicated, if at all, by an undulation. Erect propodeal setae numerous (12 or more), 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 absent. Colour foreparts orange to dark brown, usually with varying degrees of brownish infuscation in the case of lighter coloured workers, gaster brown to black, often with a coppery sheen or with bluish iridescence. Colour of erect setae pale yellowish.

Measurements. Worker (n = 17)—CI 86–93; EI 23–28; EL 0.18–0.26; EW 0.14–0.21; HFL 0.85–1.21; HL 0.77–1.01; HW 0.67–0.94; ML 0.93–1.28; MTL 0.61–0.83; PpH 0.13–0.20; PpL 0.40–0.56; SI 95–107; SL 0.7 1– 0.92.