Iridomyrmex omalonotus

Iridomyrmex omalonotus
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Formicidae
Subfamily:	Dolichoderinae
Tribe:	Leptomyrmecini
Genus:	Iridomyrmex
Species:	I. omalonotus
Binomial name
Iridomyrmex omalonotus Heterick & Shattuck, 2011

Iridomyrmex omalonotus is a very common species that has a preference for drier habitats. It makes terrestrial nests, denoted by a small mound (Renmark, South Australia: S. O. Shattuck, label data). Sandplain heath-land, 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.

Identification

The appearance of many workers of this species is that of their eastern cousins, namely Iridomyrmex mayri and Iridomyrmex 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, Iridomyrmex 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). Morphological similarities between I. omalonotus and I. obscurior are also discussed under the latter.

Keys including this Species

• Key to Iridomyrmex species

Distribution

Latitudinal Distribution Pattern

Latitudinal Range: -29.52583313° to -37.68333333°.

North Temperate	North Subtropical	Tropical	South Subtropical	South Temperate

• Source: AntMaps

Distribution based on Regional Taxon Lists

Australasian Region: Australia (type locality).

Distribution based on AntMaps

Distribution based on AntWeb specimens

Check data from AntWeb

Countries Occupied

Number of countries occupied by this species based on AntWiki Regional Taxon Lists. In general, fewer countries occupied indicates a narrower range, while more countries indicates a more widespread species.

Estimated Abundance

Relative abundance based on number of AntMaps records per species (this species within the purple bar). Fewer records (to the left) indicates a less abundant/encountered species while more records (to the right) indicates more abundant/encountered species.

Nomenclature

The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

• omalonotus. Iridomyrmex omalonotus Heterick & Shattuck, 2011: 118, figs. 60, 90 (w.) AUSTRALIA.

Type Material

• Holotype, worker, 5km S Borden, Western Australia, 239m, Australia, 34°5′0″S 118°15′0″E, 9 April 1992, S. Shattuck, ANIC32-038854, Australian National Insect Collection.
• Paratype, 5 workers, 5km S Borden, Western Australia, 239m, Australia, 34°5′0″S 118°15′0″E, 9 April 1992, S. Shattuck, ANIC32-038854, Australian National Insect Collection.
• Paratype, 3 workers, Cliff Head, Western Australia, 12m, Australia, 29°31′33″S 114°59′44″E, 20 September–9 November 2003, C. Lambkin, N. Starwick & J. Recsei, ANIC32-030807, Australian National Insect Collection; low closed mallee, malaise.
• Paratype, 2 workers, Cliff Head, Western Australia, 12m, Australia, 29°31′33″S 114°59′44″E, 20 September–9 November 2003, C. Lambkin, N. Starwick & J. Recsei, ANIC32-030807, Museum of Comparative Zoology; low closed mallee, malaise.
• Paratype, 3 workers, 46mi. SSW Coolgardie, Western Australia, Australia, 31°33′0″S 120°48′0″E, 6 November 1969, R. W. Taylor, ANIC32-032124, The Natural History Museum; trunk strays mallee.

Description

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.

Etymology

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

References

• Heterick, B.E. & Shattuck, S.O. 2011. Revision of the ant genus Iridomyrmex (Hymenoptera: Formicidae). Zootaxa 2845: 1-175.
• Heterick, B.E. 2021. A guide to the ants of Western Australia. Part I: Systematics. Records of the Western Australian Museum, Supplement 86, 1-245 (doi:10.18195/issn.0313-122x.86.2021.001-245).
• Heterick, B.E. 2022. A guide to the ants of Western Australia. Part II: Distribution and biology. Records of the Western Australian Museum, supplement 86: 247-510 (doi:10.18195/issn.0313-122x.86.2022.247-510).

References based on Global Ant Biodiversity Informatics

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