Iridomyrmex omalonotus, Heterick & Shattuck, 2011

Heterick, Brian E. & Shattuck, Steve, 2011, Revision of the ant genus Iridomyrmex (Hymenoptera: Formicidae) 2845, Zootaxa 2845 (1), pp. 1-174 : 118

Iridomyrmex omalonotus sp. n.

( Figs 60 , 90 )

Types. Holotype worker from 5km S Borden , 34°05’S 118°15’E, Western Australia, 239m, 9 April 1992, S. Shattuck ( ANIC, ANIC32-038854 ) . Paratypes: 5 workers, same data as holotype ( ANIC) ; 5 workers from Cliff Head , 29°31’33”S 114°59’44”E, Western Australia, 12 m, 20 September–9 November 2003, C. Lambkin, N. Starwick & J. Recsei, low closed mallee, malaise ( ANIC, 3 workers, MCZC, 2 workers, ANIC32-030807 ) ; 3 workers from 46mi. SSW Coolgardie 31°33’S 120°48’E, Western Australia, 6 November 1969, R. W. Taylor, trunk strays mallee ( BMNH, ANIC32-032124 ) .

Worker Description. Head. Posterior margin of head weakly convex to planar, or planar to 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 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, or weakly undulant or almost straight. Erect pronotal setae numerous (12 or more) and longest setae elongate, flexuous and/or curved, or numerous (12 or more), short and bristly. Mesonotum sinuous. Erect mesonotal setae moderate in number to numerous (6 or more), short and bristly. Mesothoracic spiracles always inconspicuous; propodeal dorsum straight and short (equal in length to propodeal declivity), or 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 sparse (6 or fewer) to 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 shades of brown, gaster may be darker than foreparts. Colour of erect setae white, depigmented.

Measurements. Worker (n = 6) — CI 76–89; EI 25–28; EL 0.18–0.22; EW 0.13–0.18; HFL 1.08–1.37; HL 0.82–0.96; HW 0.63–0.86; ML 1.03–1.34; MTL 0.81–0.97; PpH 0.12–0.17; PpL 0.41–0.52; SI 116–141; SL 0.88– 1.04.

Comments. Iridomyrmex omalonotus is a very common species that has a preference for drier habitats. The appearance of many workers is that of their eastern cousins, namely I. mayri and I. obscurior , but in a number of populations the propodeum is peculiarly flattened. However, the propodeum is variable in appearance, and efforts to find discrete characters to differentiate the most distinctive workers representing the two morphs have been unsuccessful. The view taken here is that variable propodeal shape is part of normal intraspecific variation in I. omalonotus . This ant can be distinguished from most others by its long, hairy antennal scapes, erect setae on the hind tibiae and sides of the head, and its relatively small size. Of the few species with which I. omalonotus can be confused, I. spurcus is found in the same habitat, but this species may be recognised by the unusually long setae on its legs and mesosoma (short and bristly in I. omalonotus —see species key). Morphological similarities between I. omalonotus and I. obscurior are also discussed under ‘Comments’ for the latter. Iridomyrmex omalonotus has been collected in Western Australia, Victoria, New South Wales and also South Australia, where this species makes terrestrial nests, denoted by a small mound (Renmark, South Australia: S. O. Shattuck , label data). Sandplain heathland, Triodia -covered sand dunes and mallee scrubland are typical habitats. The ant frequently ascends trees to forage, and unsurprisingly, label data indicates that a number of specimens have been collected using such methods as malaise traps and honey baits on tree-trunks. Interestingly, foragers have been collected at night (Cocklebiddy, Western Australia), although this ant is also diurnally active. On the basis of its known relationships and attraction to honey, this species is also likely to attend lycaenid caterpillars and honeydew-producing Hemiptera , although label data are lacking for this detail.

Etymology. Greek: omalus —‘flat’ plus Latin: notus —‘back’, referring to the appearance of the worker propodeum seen in profile.

Figures

FIGURE 60. Iridomyrmex omalonotus, low propodeum form (Little Desert National Park, Vic., ANIC32-030796): A. Front of head; B. Side of body; C. Top of body. Iridomyrmex omalonotus, high propodeum form (45km N Balranald, NSW, ANIC 32- 039412): D. Front of head; E. Side of body; F. Top of body; G. Distribution of material examined.

FIGURE 90. Head length versus head width for I. obscurior and I. omalonotus.