Iridomyrmex anceps

Iridomyrmex anceps is a very widespread ant that is almost ubiquitous in many northern regions of Australia, where it is generally found near the coast and at wetter inland sites. The species also has a wide range throughout the Pacific, where it has been recorded from several southern and southeast Asian countries (including China, India and Malaysia) and a variety of Pacific islands.

Identification
Iridomyrmex anceps is a nondescript brown ant. While the phenotype varies somewhat in terms of the shape of the propodeum, the short, erect, mesosomal setae and uniform brown to blackish colouration always enable Australian populations to be distinguished from the other common northern Iridomyrmex of medium size, Iridomyrmex minor, with which it is often sympatric. The relatively long antennal scape also enables it to be separated from species related to Iridomyrmex rufoniger that are of the same size and general appearance. Probably because of its generic habitus, I. anceps has been confused in the past with other medium–sized Iridomyrmex. A case in point is where a mildly invasive Iridomyrmex recognised from New Zealand (mainly from the North Island) was wrongly identified as I. anceps for many years, based on a provisional initial identification by Dr. R.W. Taylor. The exotic ant is now known to be unrelated to I. anceps (Don, 2007). The ant has recently been ascribed to ‘the suchieri group’ (A. Andersen, pers. comm. cited in Don, 2007), and, in the opinion of the present authors, is likely to be I. suchieri itself.

Distribution based on Regional Taxon Lists
Afrotropical Region: United Arab Emirates. Australasian Region: Australia, New Caledonia. Indo-Australian Region: Borneo, Cook Islands, Fiji, Indonesia, Krakatau Islands, Malaysia, Marshall Islands, Micronesia (Federated States of), New Guinea, Northern Mariana Islands, Palau, Philippines, Solomon Islands, Tokelau, Wallis and Futuna Islands. Oriental Region: Bangladesh, India, Laos, Myanmar, Taiwan, Thailand, Vietnam. Palaearctic Region: China.

Biology
Milar et al. (2017) found in an experimental test, simulating being threatened with entrapment in sand (as might happen if falling in an ant lion pit or if subjected to a collapse of a ground nest), that this species did exhibit rescue behaviour. This was in agreement with their hypothesis that species that could face entrapment situations would show such a response. Iridomyrmex anceps occur in forest situations. While they have not evolved with ant lion predation they do face possible dangers from being stuck in clay, organic debris or plant secretions. This species did show a very specific response, i.e., they responded to sand entrapment but not to a novel threat from ant lions.

Nomenclature

 *  anceps. Formica anceps Roger, 1863a: 164 (w.) WEST MALAYSIA. Karavaiev, 1926d: 433 (m.); Imai, Baroni Urbani, et al. 1984: 8 (k.). Combination in Iridomyrmex: Dalla Torre, 1893: 168. Senior synonym of excisus: Dalla Torre, 1893: 168; Forel, 1895e: 469; Emery, 1895k: 475; of papuana (and its junior synonym discoidalis): Wilson & Taylor, 1967: 78; of formosae, ignobilis, meinerti, metallescens, sikkimensis, watsonii: Heterick & Shattuck, 2011: 40. Material of the unavailable name neocaledonica referred here by Taylor, 1987a: 33. Current subspecies: nominal plus.
 * excisus. Iridomyrmex excisus Mayr, 1867a: 77 (w.q.) INDONESIA. Junior synonym of anceps: Dalla Torre, 1893: 168; Forel, 1895e: 469; Emery, 1895k: 475.
 * discoidalis. Prenolepis discoidalis Donisthorpe, 1947c: 594 (m.) NEW GUINEA. Junior synonym of papuana: Smith, M.R. 1957a: 347.
 * formosae. Iridomyrmex bicknelli r. formosae Forel, 1912a: 70 (w.q.) TAIWAN. Junior synonym of anceps: Heterick & Shattuck, 2011: 40.
 * ignobilis. Iridomyrmex anceps subsp. ignobilis Mann, 1921: 472 (w.) FIJI IS. Junior synonym of anceps: Heterick & Shattuck, 2011: 40.
 * meinerti. Iridomyrmex meinerti Forel, 1901b: 22 (q.) NEW GUINEA (Bismarck Archipelago). Junior synonym of anceps: Heterick & Shattuck, 2011: 40.
 * metallescens. Iridomyrmex rufoniger var. metallescens Emery, 1893e: 194 (w.) INDONESIA (Ambon I.). Donisthorpe, 1948b: 309 (q.m.). Junior synonym of anceps: Heterick & Shattuck, 2011: 40.
 * papuana. Iridomyrmex gracilis subsp. papuana Emery, 1897d: 572 (w.) NEW GUINEA. Forel, 1901b: 20 (q.m.). Subspecies of anceps: Forel, 1901b: 19. Senior synonym of discoidalis: Smith, M.R. 1957a: 347. Junior synonym of anceps: Wilson & Taylor, 1967: 78.
 * sikkimensis. Iridomyrmex anceps var. sikkimensis Forel, 1904c: 27 (w.) INDIA. Forel, 1907e: 18 (q.). Junior synonym of anceps: Heterick & Shattuck, 2011: 40.
 * watsonii. Iridomyrmex anceps var. watsonii Forel, 1895e: 468 (diagnosis in key) (w.) MYANMAR. Junior synonym of anceps: Heterick & Shattuck, 2011: 40.

Type Material


Types. Formica anceps Roger: Neotype worker (top worker, here designated) from Kuala Lumpur, Malaysia, 9 February 1967, D.H. Murphy, on sand, A-290-1 (, ANIC32-036430). Iridomyrmex excisus Mayr: Syntypes from "Coloniae indo-neerlandicae" (not located during this study). Iridomyrmex rufoniger metallescens Emery: Holotype worker from Ambon (as Amboina), Maluku, Indonesia (, examined). Iridomyrmex anceps watsonii Forel: Syntype workers and queen from upper Myanmar (, 3 workers, 1 queen, examined). Iridomyrmex gracilis papuana Emery: Syntype workers from Kapakapa, Papua New Guinea (, 1 worker, examined). Iridomyrmex meinerti Forel: Holotype queen from Rabaul (as Ralum), East New Britain, Papua New Guinea (not located during study, apparently lost). Iridomyrmex anceps sikkimensis Forel: Syntype workers from Sikkim and Garo Hills, Assam, India. Iridomyrmex bicknelli formosae Forel: Syntype workers and queens from Peinan (as Pilam), Taiwan (, 1 queen, examined). Iridomyrmex anceps ignobilis Mann: Syntypes from Nadarivatu, Viti Levu, Fiji (, 3 workers, examined). Prenolepis discoidalis Donisthorpe: Holotype male from K. B. Mission, Milne Bay, Papua New Guinea (, examined).

Type material for I. anceps could not be located during this study, and, given the number of years since the species was described and the damage caused to museums and similar institutions during WWII, has probably been destroyed. A worker (top specimen on a pin of two workers) collected from Malaysia is here designated a neotype to give stability to the name. The erection of a neotype is a necessary task, since the name ‘anceps’ has been assigned promiscuously to various common species of Iridomyrmex in the past, as mentioned above, and this has caused considerable confusion—despite the fact that the original description is sufficiently detailed to make the identity of an Iridomyrmex anceps worker a matter that is not difficult to establish. Type material of I. meinerti could also not be located during this study. While Forel (1901) states that the single queen on which this taxon is based is highly distinctive (and thus he decided to base this taxon on this single specimen), the description meets the concept of I. anceps developed here. Because of this, I. meinerti is here treated as a synonym of I. anceps until either the type is located or a suitable specimen is selected as a replacement type, at which time the status of this name can be reassessed.

Description
Worker Description. Head. Posterior margin of head planar to weakly concave; erect setae on posterior margin in full-face view set in a row, or present in small aggregations on one or both sides of posterior margin of head, or present singly or as a couple of setae on either side of posterior margin of head; 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). Number of ocelli one (a minute ocellus), position of obsolete ocelli indicated by small pits only or pits lacking, or ocelli absent; in full-face view, eyes set at about midpoint of head capsule; in profile, eye set around midline of head capsule; eye semi-circular, or elongate. 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, or absent, except at tip; prominence on anteromedial clypeal margin projecting as triangular spur; 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 moderate in number (6–12), short and bristly, or sparse to absent. Mesonotum straight. Erect mesonotal setae varying from absent to numerous (12 or more), short and bristly (when present). Mesothoracic spiracles prominent or inconspicuous; propodeal dorsum smoothly and evenly convex, 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 moderate in number (6–12), short and bristly. Petiole. Dorsum of node convex, or planar; node thin, scale-like, orientation more-or-less vertical, or thin, scale-like, orientated anteriad. Gaster. Non-marginal erect setae of gaster present or absent on first gastral tergite; marginal erect setae of gaster present on first tergite. General characters. Allometric differences between workers of same nest present. Colour uniformly light to dark brown. Colour of erect setae pale, whitish.

Measurements. Worker (n = 11)—CI 84–97; EI 24–30; EL 0.21–0.28; EW 0.16–0.23; HFL 1.09–1.55; HL 0.82–1.20; HW 0.70–1.17; ML 1.08–1.61; MTL 0.79–1.11; PpH 0.14–0.22; PpL 0.42–0.62; SI 104–134; SL 0.93– 1.22.