Iridomyrmex purpureus

This species forms large pebble mounds with multiple nest holes. Wherever it occurs, I. purpureus is extremely pugnacious, and workers will pour out of entrance holes to attack any person or other creature that disturbs their nest. Workers forage on the ground and will also ascend trees in search of nectar and honeydew.

Identification
Physically, I. purpureus workers are difficult to distinguish from Iridomyrmex lividus, and these two species form a complex, along with the much more localised Iridomyrmex spadius, that can be distinguished from other meat ant complexes by the shape of the pronotum when seen in profile.

Apart from the variation in colour used to separate I. purpureus and its junior synonym, I. greensladei, I. purpureus populations exhibit an unsettling polymorphism in other respects, some in the extreme south-west of Western Australia referable to I. greensladei having erect setae on the genae while those outside that region have glabrous genae. Shattuck (1993a) found this pattern to be likely clinal. The colour of the erect setae found on all parts of the body, and to some degree the iridescence, can also vary: I. purpureus with pale setae are confined to the extreme south coast of Western Australia, compared with a much broader distribution for those populations possessing the normal, blackish setae. Again, Shattuck (1993a) could not separate the pale setae form from remaining populations of I. ‘greensladei’ when other characters were considered. A tendency to pale greenish-blue to yellowish-green iridescence is also found in specimens from the Western Australian wheatbelt and goldfields, particularly on the humeri and the frons, but this is a more subtle character than the other two mentioned, and there is no hard-and-fast distinction between these and other members of the taxon. The difference in colour is much less marked, for example, than colour differences between Iridomyrmex viridiaeneus (also found in drier parts of the south-west) and all samples of I. purpureus seen. Other variants mentioned by Shattuck (1993a) include workers with reduced appressed pubescence on the first gastral tergite (found in South Australia and the Northern Territory).

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Biology
Moulds (2006) - Iridomyrmex purpureus workers have been observed entering a mine, collecting fresh bat guano and carrying it back to their nest. Guano is known to be eaten directly by many guanobitic and guanophilic invertebrates as a high nitrate food, or, more commonly the more for its readily digested glycogen rich bacteria and fungus.

Brooker (2007) - On the afternoon of 4 October 2004, I watched a pair of Chestnut-rumped Thornbills Acanthiza uropygialis in the vicinity of a Wheatbelt Wandoo Eucalyptus capillosa, that contained a hollow in which the birds had previously nested. For 30 minutes the pair fluttered to the trunk of the wandoo and pecked at meat ants that were moving on it. After each attack, an ant fell to the ground and I surmised that the birds were defending their eggs or nestlings. However, the nest was not occupied. A more likely explanation of this unusual behaviour could be that the thornbills were robbing the ants of the small white items (perhaps lerps) they were carrying. Splendid Fairy-wrens Malurus splendens will often rob meat ants moving on their trails and mounds (Rowley and Russell 1997 in Fairy-wrens and Grasswrens, Oxford University Press: Oxford; and personal observation), but I have not previously seen this foraging technique undertaken arboreally or by thornbills.

Hölldobler & Carlin (1985) - In Iridomyrmex purpureus, most new colonies are founded by single queens, following the nuptial flight in the spring month of October. Sixty-five of 72 newly founded nests excavated near Canberra contained a single queen, six contained two queens, and one contained three queens. As the nearby inseminated queens scurry over the ground and then start to dig a burrow in the soil, they are attacked by many enemies. Greaves and Hughes (1974) reported losses of 80 percent or higher from ground-feeding birds alone. Many other queens are killed by hostile workers of their own species when they stray too near the established colonies. But, surprisingly, other queens succeed in digging their nest chambers in the immediate vicinity of mature Iridomyrmex purpureus. Not only are most of these females tolerated by the resident workers, they are often attended and protected. The workers even help them dig the chambers (see Figure 6-1). Such actions are likely to protect the foundresses from hostile ants, birds, and other predators. Meat ant workers are extremely aggressive, biting enemies and spraying them with poisonous secretions from their pygidial glands. Hölldobler and Carlin believe that the queens protected in this manner are the ones fortunate enough to settle near their natal nests, so that the foundresses are also likely to be absorbed into the mother colonies to become supernumerary queens. Thus variation in queen numbers appears to be due at least in part to the vicissitudes of foundress association and tolerance by neighboring mature colonies.

Nomenclature

 * aeneum. Liometopum aeneum Mayr, 1862: 704 (q.) AUSTRALIA. Junior synonym of purpureus: Mayr, 1876: 81.
 * castrae. Iridomyrmex detectus var. castrae Viehmeyer, 1925a: 31 (w.) AUSTRALIA. Subspecies of purpureus: Taylor & Brown, D.R. 1985: 102. Junior synonym of purpureus: Shattuck, 1993a: 128.
 * detecta. Formica detecta Smith, F. 1858b: 36 (q.) AUSTRALIA. Wheeler, G.C. & Wheeler, J. 1974b: 398 (l.); Crozier, 1968a: 25 (k.). Combination in Iridomyrmex: Dalla Torre, 1893: 168. Junior synonym of purpureus: Lowne, 1865a: 275; Mayr, 1876: 81; Taylor & Brown, D.R. 1985: 102.
 * greensladei. Iridomyrmex greensladei Shattuck, 1993a: 122, fig. 11 (w.q.m.) AUSTRALIA. Junior synonym of purpureus: Heterick & Shattuck, 2011: 124.
 * horni. Camponotus horni Kirby, W.F. 1896: 205 (w., not q.) AUSTRALIA. Junior synonym of purpureus: Clark, 1930c: 20. See also: Shattuck, 1993a: 128.
 *  purpureus. Formica purpurea Smith, F. 1858b: 40 (w.) AUSTRALIA. Lowne, 1865a: 275 (m.); Imai, Crozier & Taylor, 1977: 345 (k.). Combination in Iridomyrmex: Mayr, 1862: 702. Senior synonym of detecta: Lowne, 1865a: 275; of smithii: Mayr, 1870b: 955; of aeneum: Mayr, 1876: 81; of horni: Clark, 1930c: 20; Shattuck, 1993a: 128; of castrae: Shattuck, 1993a: 128; of greensladei: Heterick & Shattuck, 2011: 124. See also: Greaves, 1971: 15; Shattuck, 1993a: 128; Shattuck, 1994: 109.
 * smithii. Formica smithii Lowne, 1865a: 276 (w.) AUSTRALIA. Junior synonym of purpureus: Mayr, 1870b: 955; Taylor & Brown, D.R. 1985: 102.

Taxonomic Notes
Iridomyrmex greensladei (Shattuck, 1993a) is supposedly separated from I. purpureus by the hue of its head and pronotum, which are concolorous with the rest of the mesosoma (lighter than the rest of the mesosoma in I. purpureus). The two nominal species were regarded as nonsympatric by Shattuck (his figures 11 and 13 form a nice symmetry). Additional evidence adducing that I. greensladei and I. purpureus were separate came from Halliday (1979 and 1981) who examined the enzymes esterase and amylase within the I. purpureus species-group. That researcher found differing amylase allele frequencies that suggested that I. purpureus and I. greensladei clustered into two separate groups (along with other meat ant forms). However, research during the present study has failed to recover a clear distinction in colour between a number of eastern and western populations of meat ants formerly categorised as ‘greensladei’ and ‘purpureus’, namely, some Western Australian populations have a head that is paler than the mesosoma, and vice-versa for some eastern states populations. Moreover, much worker material is indeterminate as to colour. Unpublished mitochondrial DNA (using the CO 1 gene) has also failed to authoritatively distinguish western and eastern populations of ‘greensladei’ and ‘purpureus’; indeed, the distance between the terminals falls well within what is normally regarded as acceptable for populations of the same species (&lt;&lt; 0.1 substitutions/site). The two nominal species also strongly overlap in regards to a number of morphometric measurements.

The work of Halliday notwithstanding, the evidence thus suggests that the common reddish meat ants of eastern and western Australia are conspecific. However, there is a caveat: the form found in the Yorke Peninsula in South Australia, and identified by Greenslade (1987) as ‘small purple’ or SP, was intended to be the same as I. greensladei. Although these ants are morphologically indistinguishable from some Western Australian I. greensladei and many I. purpureus (both of which have multiple entrance mound nests), they supposedly have a single nest entrance (Greenslade, 1987). However, Shattuck chose workers from Israelite Bay, Western Australia, 1000 km west of the Yorke Peninsula, for his I. greensladei holotype and paratypes, respectively. This means that the form SP found in the Yorke Peninsula (which has not thus far been subject to CO 1 analysis) may yet prove to be genetically distinct, albeit morphologically cryptic. The decision made here is to treat the currently existing taxa represented by the eastern I. purpureus and the Western Australian ‘I. greensladei’ as conspecific, with the latter name falling into synonymy: potentially, a new name could be erected if future research revealed the Yorke Peninsula ants were indeed a separate species.

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, or 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 3 x its diameter, or 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. '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 protuberant, or smoothly and evenly convex; 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; 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 of head and often pronotum orange to brick-red, mesonotum and propodeum lighter than, concolorous with or darker than the head, gaster brown to black, legs orange to brown, foreparts with bluish, pink, pale greenish-yellow or purple iridescence, gaster with greenish, bluish or purple iridescence. Colour of erect setae brown.

Measurements. Worker (n = 84)—CI 89–103; EI 17–22; EL 0.33–0.42; EW 0.18–0.26; HL 1.69–2.3 1; HW 1.5 1–2.29; ML 0.76–1.26; PpH 0.21–0.44; PpL 0.83–1.28; SI 86–104; SL 1.57–2.05.

References based on Global Ant Biodiversity Informatics

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