Iridomyrmex alpinus

Iridomyrmex alpinus is confined to very wet and often montane areas in New South Wales, Victoria and Tasmania. In fact, it has been taken in alpine vegetation at elevations in excess of 2000 m. Label data indicates that, within its range, the species is very adaptable in terms of habitat: ants have been sampled from a variety of cool temperate vegetation types, including alpine meadows and grassland, the edge of rainforests and open, wet sclerophyll forest. The appearance of the nests also varies, so that the nest entrance can be either a simple hole in the ground or a mound (the latter, presumably, in a mature colony). Conversely, the ants can establish their nest under cover (e.g., a stone), in rotting wood, under piles of dead leaves and twigs or in sphagnum moss. One New South Wales worker is described as being taken from the nest of ‘a stick ant’. Workers have been found foraging in litter and on alpine vegetation. Collection methods have been various; hand collections, pitfall traps, berlesates and even a human dung trap! This species, unlike most ants, does not mind nesting in wet soil, and a number of the collections have been taken adjacent to waterways. All in all, the large amount of material available for study suggests that this species is an important component of the eastern seaboard ant fauna in phytogeographic areas and in physical habitats that would support few ant species and very few Iridomyrmex.

Identification
While closely related to Iridomyrmex conifer, Iridomyrmex setoconus and Iridomyrmex turbineus and sharing a number of characters with them, I. alpinus can be readily separated by its lack of a strongly conical propodeal dorsum and its biogeography (it is eastern while the others occur in southern Western Australia). The ant can also be separated from the morphologically similar Iridomyrmex pallidus and Iridomyrmex hartmeyeri in terms of biogeography and habitat preference and the shape and size of the eye (small-medium and oval versus large and asymmetrical).

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  alpinus. Iridomyrmex alpinus Heterick & Shattuck, 2011: 39, fig. 9 (w.) AUSTRALIA.

Types. Holotype worker from 12km W Orroral Tracking Station, ACT, 25 November 1990, S. O. Shattuck, dry sclerophyll (, ANIC32-059637). Paratypes: 8 workers, same data as holotype (, ANIC32-038488); 15 workers from 2 miles N Mount Aggie, 4500ft., ACT, 25 August 1966, R. W. Taylor, wet sclerophyll (, ANIC32-040860, 9 workers;, ANIC32-040860, 3 workers; , ANIC32-040860, 3 workers); 6 workers from Mount Aggie, 4700ft., 5 November 1966, R. W. Taylor (, ANIC32-040862).

Description
Worker Description. Head. Posterior margin of head planar to weakly concave; erect setae on posterior margin absent; sides of head noticeably convex; erect genal setae 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 straight; antennal scape surpassing posterior margin of head by 1-2 x its diameter. Erect setae on scape absent, except at tip; prominence on anteromedial clypeal margin present as an indistinct swelling or undulation; mandible triangular with distinct angle between masticatory and basal margins; long, curved setae on venter of head capsule absent. Mesosoma. Pronotum strongly inclined anteriorly. Erect pronotal setae sparse to absent. Mesonotum straight. Erect mesonotal setae sparse to absent. Mesothoracic spiracles prominent or inconspicuous; propodeal dorsum protuberant; 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 lacking or very minute (one or two tiny setae present). Petiole. Dorsum of node acuminate, or convex; node thin, scale-like, orientation more-or-less vertical. Gaster. Non-marginal erect setae of gaster present or absent on first gastral tergite; marginal erect setae of gaster present on first tergite, or absent on first tergite. General characters. Allometric differences between workers of same nest absent. Colour concolorous medium brown to black. Colour of erect setae light brown.

Measurements. Worker (n = 13)—CI 90–101; EI 21–24; EL 0.18–0.24; EW 0.10–0.16; HFL 1.18–1.18; HL 0.82–1.13; HW 0.75–1.12; ML 0.32–0.49; MTL 0.87; PpH 0.12–0.21; PpL 0.42–0.60; SI 85–98; SL 0.73–0.98.

Etymology. Latin: ‘alpine’ (mountain), referring to the common habitat of this species.

References based on Global Ant Biodiversity Informatics

 * CSIRO Collection
 * Heterick B. E., and S. Shattuck. 2011. Revision of the ant genus Iridomyrmex (Hymenoptera: Formicidae). Zootaxa 2845: 1-174.
 * Heterick, B., and S. O. Shattuck. "Revision of the ant genus Iridomyrmex (Hymenoptera: Formicidae)." Zootaxa 2845 (2011): 1-174.