Iridomyrmex rufoniger (Lowne)

Heterick, Brian E. & Shattuck, Steve, 2011, Revision of the ant genus Iridomyrmex (Hymenoptera: Formicidae) 2845, Zootaxa 2845 (1), pp. 1-174 : 133-135

Iridomyrmex rufoniger (Lowne)

( Figs 69 , 92 )

Formica rufonigra Lowne 1865a: 279 .

Iridomyrmex rufoniger septentrionalis Forel, 1902: 465 (first available use of Iridomyrmex rufoniger r. pallidus var. septentrionalis Forel, 1901: 23 , an unavailable infrasubspecific name). New synonym.

Acantholepis mamillatus Lowne, 1865b: 333 (combination in Hypoclinea by Mayr, 1870: 995; junior synonym of I. rufoniger (Lowne) by Mayr, 1876: 82).

Iridomyrmex rufoniger domestica Forel, 1907a: 291 . New synonym.

Types. Formica rufonigra Lowne : Neotype worker (here designated) from Camden Haven, New South Wales, 18 November 1985, D.S. Horning, Jr., sweeping ocean beach vegetation (ANIC, ANIC32-038679 ; 13 additional workers from same series: ANIC, 8 workers; BMNH, 2 workers; MCZC, 3 workers). Iridomyrmex rufoniger septentrionalis Forel : Syntypes from Mackay, Queensland (ANIC, 2 workers, examined; MCZC, 2 workers, examined; MHNG, 12 workers, 3 queens, 14 males; NHMB, 1 worker). Acantholepis mamillatus Lowne : Syntypes from Sydney, New South Wales (BMNH, 1 worker, examined). Iridomyrmex rufoniger domestica Forel : Syntypes from Howlong , New South Wales (ANIC, 4 workers, examined); Richmond , New South Wales (ANIC, 3 workers, examined; MHNG, 14 workers, 5 queens, 19 males; NHMB, 1 worker, 1 male (missing gaster); OXUM, 2 workers, 1 male) and Sydney , New South Wales (MCZC, 3 workers, examined).

Worker Description. Head. Posterior margin of head weakly concave, or strongly 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 at about 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 1–2 x its diameter. Erect setae on scape present and abundant, or present and sparse, or absent, except at tip; prominence on anteromedial clypeal margin projecting as blunt but distinct protuberance; mandible regular triangular with oblique basal margin; long, curved setae on venter of head capsule absent. Mesosoma. pronotum strongly inclined anteriorly. Erect pronotal setae numerous (12 or more) and longest setae elongate, flexuous and/or curved. Mesonotum straight. Erect mesonotal setae moderate in number (6–12), short and bristly. Mesothoracic spiracles always inconspicuous; 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 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 orange to dark brown, head and gaster usually darker than mesosoma, gaster with bluish, bluish-purple or yellowish-green iridescence. Colour of erect setae depigmented yellow.

Measurements. Worker (n = 10)—CI 91–98; EI 22–25; EL 0.19–0.25; EW 0.15–0.20; HFL 0.93–1.24; HL 0.84–1.11; HW 0.79–1.08; ML 1.03–1.47; MTL 0.70–0.90; PpH 0.16–0.21; PpL 0.45–0.60; SI 84–96; SL 0.74– 0.92.

Comments. Iridomyrmex rufoniger , along with the meat ants ( I. purpureus group), I. chasei and I. suchieri , is the Iridomyrmex with which the Australian public is most familiar. At least on the eastern seaboard, this species is at much at home on urban paths and verges and in backyards as it is in dry sclerophyll woodland, thick forest or heathland. Throughout its wide range I. rufoniger is morphologically variable, but not excessively so, with the result that identification is less problematic than in more morphologically polymorphic species such as I. dromus and I. minor . Typically, this species is a squat, broad-headed, short-scaped (SI 84-96), medium-sized Iridomyrmex with bluish- or yellowish-green iridescence on the gaster. Erect setae are always present on the hind tibiae but, except for a few isolated populations, are absent from the antennal scapes and the sides of the head. The pronotum is often noticeably humped, as with chasei , gibbus and difficilis (many workers), but the combination of erect hind tibial setae, size ( gibbus and difficilis are much smaller with glabrous hind tibial setae) and lack of generalised iridescence on the gaster ( I. chasei ) will separate out workers of these species from workers of I. rufoniger . The most troublesome variation is seen in ants from the coastal regions of New South Wales, especially around Sydney. Here, there are populations consisting of small, dark workers with relatively narrow heads. The setae on the hind tibiae are small, inconspicuous and few in number, often just one or two near the base of the tibiae. In such cases, both hind tibiae should be checked and, if available, several workers should be examined, to ensure they can be separated from I. victorianus , which has glabrous tibiae. However, the more compact mesosoma, raised promesonotum and shorter antennal scapes of I. rufoniger (surpassing the posterior margin of the head by 1 ≤ × their greatest diameter, versus surpassing the posterior margin of the head by 1.5 ≥ × their greatest diameter in I. victorianus ) can be used as definitive characters if the specimen is abraded. Narrow-headed workers can also be seen in some Queensland populations, but these are relatively hairy and pose no particular issues as far as recognition is concerned. Some hairy eastern populations of I. suchieri (I. ‘ obscurus ’) may also resemble I. rufoniger workers, but the pronotum in the former species is more undulant than humped, and the propodeal dorsum is relatively straight and rounds over into the propodeal declivity through a distinct angle.

This ant is found in a variety of habitats in all mainland Australian states, although it appears to be rare in the Northern Territory and absent from the wet south-west corner of Western Australia for reasons that are unclear (one very old series from ‘Perth, WA’ is questionably from that locality). Specimens of the relatively glabrous coastal New South Wales phenotype have been intercepted in NZ at the ports of Auckland and Freyberg, but the species has not yet become established in NZ. Additionally, there is a single, very old series from a farm in New Caledonia, where the ant has almost certainly been introduced. Behaviourally, this species is typical of the smaller Iridomyrmex . Nests, which may be numerous within a given area, are made into soil, and the ants are dominant where they occur. Around the Western Australian goldfields town of Westonia this species is the most conspicuous ant in mine dumps, but is much less common in surrounding rehabilitated bushland. As with the morphologically similar and closely related I. chasei , I. rufoniger nests have a crater of loose dirt at the entrance, and workers may forage nocturnally as well as diurnally. Some nests are also made under stones. Workers will ascend eucalypts in search of nectar and honeydew, and label data also records scavenging of dead insects. There is, in fact, a considerable amount of label data on the dietary preferences of this species: the ants are known to tend the scale Saisettia oleae and the aphid Aphis hederae , as well as tend larvae of at least four lycaenid butterflies, namely, Jalmenus daemeli , J. evagoras , J. icilius and Ogyrus zosine. Foraging on the flowers of Leptospermum is also noted on several labels. This species has been known to enter Canberra houses, but accompanying label data note it is not a serious urban pest.

The original type material for I. rufoniger has not been located in any of the museums accessed during this study, and is believed lost. A neotype has been chosen to represent this taxon, which is commonly referred to in the myrmecological literature, and has been given species-group name status by generations of researchers. This neotype combines features that are consistent with the description of the original specimen (a description that is admittedly scant by modern criteria, but includes references to colour and antennal scape length), and was collected from coastal New South Wales, 380 km N of Sydney. (Note: The original specimen was collected ‘in the vicinity of Sydney’). Since the taxon has attracted several species-level and subspecies-level names, the erection of a neotype is designed to give stability to this name. The neotype worker also conforms in its appearance to the description of the subspecies I. rufoniger domestica (here a junior synonym) in which the author Forel provides further diagnostic information regarding the nominal species rufoniger .

Figures

FIGURE 69. Iridomyrmex rufoniger (Canberra, ACT, ANIC32-023677): A. Front of head; B. Side of body; C. Top of body; D. Distribution of material examined (excluding the introduced New Zealand population).

FIGURE 92. Scape length versus head width for I. anceps, I. curvifrons, I. elongatus, I. minor, I. rufoniger and I. suchieri.