Iridomyrmex coeruleus

Iridomyrmex coeruleus has a wide distribution throughout northern Australia, extending into New Guinea and the islands off Queensland, but is nowhere particularly common. Workers foraging on trees and vegetation have been collected by pan traps and sweeping.

Identification
Iridomyrmex coeruleus is a black to brownish species (lighter coloured populations are mainly outside Australia), with large eyes, broad head, short, bristly, whitish setae on the mesosoma, and antennal scapes that are paler than the head capsule. Most, but not all populations also possess an attractive blue sheen, hence the name. Others have a more coppery appearance. Specimens seen have fine, long, whitish setae on the underside of the head capsule. The presence of the long, gular setae and pale antennae will separate this species from Iridomyrmex splendens and Iridomyrmex mjobergi, the species with which it can be most easily confused, while the distinctly scalloped anterior clypeal margin and distinct anteromedial clypeal prominence separate it from Iridomyrmex niger and Iridomyrmex hertogi.

Distribution based on Regional Taxon Lists
Australasian Region: Australia. Indo-Australian Region: New Guinea.

Nomenclature

 *  coeruleus. Iridomyrmex coeruleus Heterick & Shattuck, 2011: 63, fig. 24 (w.) AUSTRALIA.

Description
Worker Description. Head. Posterior margin of head planar to weakly concave; erect setae on posterior margin in full-face view, present in small aggregations on one or both sides of posterior margin of head, or in full-face view, present singly or as a couple of setae on either side of posterior margin of head; 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 at about midpoint of head capsule; in profile, eye set anteriad of head capsule; eye semi-circular. Frontal carinae convex; antennal scape not attaining posterior margin of head (some workers) or surpassing posterior margin of head by 1–2 x its diameter (most workers). Erect setae on scape 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 present. Mesosoma. Pronotum moderately and evenly curved over its length. Erect pronotal setae sparse (6 or fewer) to moderate in number (6–12), short and bristly. Mesonotum evenly curved. Erect mesonotal setae sparse (6 or fewer) and bristly. Mesothoracic spiracles always inconspicuous; propodeal dorsum smoothly and evenly convex; placement of propodeal spiracle posteriad and near 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 sparse (6 or fewer) and bristly. Petiole. Dorsum of node convex; node thick, 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 typically uniformly dark brown to black with generalized pale bluish-green to blue iridescence, but may be iridescence may be reduced to coppery reflections (northern Western Australia). Colour of erect setae yellow.

Measurements. Worker (n = 5)—CI 88–95; EI 26–29; EL 0.21–0.28; EW 0.17–0.20; HFL 0.87–1.14; HL 0.84–1.04; HW 0.74–0.98; ML 0.94–1.33; MTL 0.64–0.83; PpH 0.13–0.18; PpL 0.38–0.56; SI 91–99; SL 0.73– 0.93.

Etymology
Latin: ‘coeruleus’ (also ‘caeruleus’ )—‘blue’, referring to the blue iridescence seen in many workers.