Iridomyrmex viridiaeneus

Iridomyrmex viridiaeneus is the most widely distributed of the meat ants, and occurs throughout Australia. Its compound nests and habits, at least in Western Australia, approximate those of species like Iridomyrmex purpureus.

Identification
This ant is distinguished by its strong green iridescence, in addition to purple or pink iridescence, and its uniformly dark, reddish integument. With older, pinned material, workers of this species may be a little difficult to distinguish from Western Australian workers of I. purpureus with yellowish- to bluish-green humeri and a bluish- green frons, but the green colour in I. viridiaeneus is quite distinct on the sides of the head capsule when the ant is seen in profile, whereas this is not the case with the I. purpureus variant. Other intraspecific variations seen in Western Australian workers (i.e., a tendency to reddish iridescence, and a more arched posterior pronotum), are discussed by Shattuck (1993 a). Shattuck also mentions in his monograph a small form of I. viridiaeneus (called ‘SB’ by the earlier researchers Greenslade and Halliday (1982)), which he considered to be conspecific with the typical, larger form.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Biology
Greenaway (1981) examined trailing activity in this species. He found it restricted to the hours of daylight and further limited by the temperature of the air surrounding the ant (T,) and by the net radiant heat load. Activity in winter begins well after sunrise and continues until late afternoon averaging c. 7.4 h per day. Midsummer activity occupies two distinct periods, one commencing at dawn and the other in late afternoon; the two together total about 6.8 h per day. The upper and lower values of T, between which ants are active are 43.5°C and 14°C. Radiant heat input is dissipated from the ants by convective heat loss.

Nomenclature

 *  viridiaeneus. Iridomyrmex detectus var. viridiaeneus Viehmeyer, 1914b: 41 (w.) AUSTRALIA. Wheeler, W.M. 1915g: 811 (q.). Wheeler, G.C. & Wheeler, J. 1974b: 400 (l.). Raised to species: Wheeler, G.C. & Wheeler, J. 1974b: 400. Subspecies of purpureus: Greenslade, 1974: 247; Taylor & Brown, D.R. 1985: 102. Raised to species: Shattuck, 1993a: 142. See also: Shattuck, 1994: 113; Heterick & Shattuck, 2011: 155.

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 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 semi-circular. Frontal carinae convex; antennal scape surpassing posterior margin of head by approximately 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 in some workers. Mesosoma. Pronotum moderately and evenly curved over its length. Erect pronotal setae numerous (12 or more), short and bristly. Mesonotum sinuous. Erect mesonotal setae numerous (12 or more), short and bristly. Mesothoracic spiracles always prominent as small, vertical protuberances; propodeal dorsum smoothly and evenly convex; placement of propodeal spiracle posteriad and near propodeal declivity, or 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 present. Colour foreparts shades of reddish-brown, head often slightly lighter in colour, gaster dark reddish-brown, iridescence on head and pronotum predominantly bright yellowish-green to emerald green, mesonotum, propodeum and legs also with pink to purple iridescence in pinned material, gaster with iridescence of rainbow hues. Colour of erect setae brown.

Measurements. Worker (n = 71)—CI 89–101; EI 17–22; EL 0.29–0.41; EW 0.18–0.26; HL 1.55–2.37; HW 1.40–2.34; ML 0.73–1.37; PpH 0.19–0.47; PpL 0.73–1.32; SI 84–108; SL 1.5 1–2.05.