Iridomyrmex roseatus

Iridomyrmex roseatus has a generally northern temperate and tropical distribution in Australia, and is recorded from all states except Victoria and Tasmania, and is common in drier areas. Workers have been collected in a variety of arid and semi-arid localities, often in mallee or mulga woodlands. Several series have been captured in malaise traps, and the species has been taken at Hakea blossoms. The habits of this medium-large ant are likely to be similar to those of meat ants, but details of behaviour and nest structure are lacking. Note that this species was recognised by Forel, who coupled it with Iridomyrmex mayri, but his name is unavailable (quadrinomial), and the association with I. mayri and relatives is tenuous.

Identification
The phylogenetic position of I. roseatus is uncertain, based purely on morphology. The strong anteromedial clypeal spur is identical with that seen in the I. purpureus species-group, but the long antennal scape with its paucity of erect setae and its mesosomal features suggest that it may belong elsewhere. Species related to Iridomyrmex mayri all lack a prominent anteromedial clypeal spur, and only Iridomyrmex spurcus is found in the more northerly regions of Australia. Possibly, I. roseatus is close to Iridomyrmex anceps and relatives, somewhere near Iridomyrmex minor. The features mentioned here ensure that this ant cannot be confused with any other. Iridomyrmex azureus comes very close, but its hind tibiae are glabrous, whereas hairy versions of I. minor itself lack iridescence (always present in I. roseatus).

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  roseatus. Iridomyrmex roseatus Heterick & Shattuck, 2011: 128, figs. 66, 89 (w.) AUSTRALIA.

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 above 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 0.2–0.5 x its length. Erect setae on scape present and sparse; prominence on anteromedial clypeal margin projecting as triangular spur; mandible elongate triangular with oblique basal margin; long, curved setae on venter of head capsule absent. 'Mesosoma. 'Pronotum moderately and evenly curved over its length, or weakly undulant or almost straight. Erect pronotal setae numerous (12 or more) and longest setae elongate, flexuous and/or curved. Mesonotum straight. Erect mesonotal setae numerous (12 or more), short and bristly. Mesothoracic spiracles always prominent as small, vertical protuberances; propodeal dorsum straight and long (half as long again as length of propodeal declivity); placement of propodeal spiracle mesad, more than its diameter away from propodeal declivity; propodeal angle 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 acuminate, or 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 or reddish, gaster and legs brown to black, iridescence on foreparts usually pink, iridescence on gaster bluish to greenish-yellow. Colour of erect setae pale yellow to whitish.

Measurements. Worker (n = 6)—CI 86–91; EI 22–24; EL 0.26–0.32; EW 0.20–0.25; HFL 1.94–2.23; HL 1.26–1 .56; HW 1.09–1.37; ML 1.74–2.10; MTL 1.45–1.66; PpH 0.23–0.30; PpL 0.63–0.81; SI 110–127; SL 1.38– 1.56.

Etymology
Latin: ‘dressed in pink’.

References based on Global Ant Biodiversity Informatics

 * Fisher J., L. Beames, B. J. Rangers, N. N. Rangers, J. Majer, and B. Heterick. 2014. Using ants to monitor changes within and surrounding the endangered Monsoon Vine Thickets of the tropical Dampier Peninsula, north Western Australia. Forest Ecology and Management 318: 7890.
 * Heterick B. E., and S. Shattuck. 2011. Revision of the ant genus Iridomyrmex (Hymenoptera: Formicidae). Zootaxa 2845: 1-174.