Monomorium fieldi

Almost as ubiquitous as Monomorium sydneyense. Probably the most common species, apart from M. sydneyense, in Perth streets and gardens (Heterick 2009).

Identification
Heterick (2001) - Monomorium fieldi poses some very considerable taxonomic, even systematics problems. Typically, these are small, shining Monomorium with a smoothly convex promesonotum, moderately wide head capsule, a deeply impressed metanotal groove, erect and suberect setae on the alitrunk and head capsule, a cuneate petiolar node, very small or vestigial metapleural lobes, and are uniformly yellowish or reddish brown to chocolate in colour.

The synonym Monomorium laeve nigrus is very different. The three syntypes and similar specimens of M. laeve nigrius are smaller than typical M. fieldi, the promesonotum is flattened, the head capsule is narrow, the scapes are shorter than in M. fieldi, the propodeum is long and low (like M. laeve), and the petiolar node is distinctly conical. Monomorium laeve nigrus also usually has a yellowish or reddish tinge to the cuticle.

When compared with many Monomorium sydneyense workers, M. laeve nigrius is not easily characterised. The latter fits neatly into a morphological continuum of workers showing apparent convergence between M. fieldi and M. sydneyense. Some Monomorium that have been assigned to M. fieldi because of the presence of erect and suberect setae on the alitrunk and a smooth propodeum, also resemble M. sydneyense in having a flattened promesonotum, and a hint of longitudinal carinae corresponding to extended metapleural lobes. These specimens also possess the rectangular head capsule, short antennal scapes, and the paler appendages seen in M. sydneyense, and are rather smaller than unambiguous M. fieldi. In a few cases the petiolar node is sharply tapered and bereft of long setae. This feature also occurs in some M. sydneyense populations. Most M. laeve nigrius-like specimens have been collected in southeast Queensland, in parts of inland New South Wales, and on the Fleurieu Peninsula in South Australia.

M. fieldi and M. sydneyense are ubiquitous throughout Australia, including Tasmania. Both are considered to be distinct and recognisable throughout most of their range, although, aside from the M. laeve nigrius morph, worker specimens with a mosaic of M. fieldi and M. sydneyense characters do occur.

For taxonomic convenience, M. laeve nigrius and Monomorium fraterculus are synonymised with M. fieldi. Specimens of each of these varieties will key out under M. fieldi, rather than M. sydneyense, in the worker key provided. (Monomorium fraterculus barretti, although similar to M. fraterculus, has the characteristic pilosity of M. sydneyense, and is discussed under that species.)

Heterick (2009) - A small, usually hairy, dark brown ant.

Distribution based on Regional Taxon Lists
Australasian Region: Australia, Lord Howe Island, New Zealand, Norfolk Island.

Biology
Heterick (2001) - Monomorium fieldi is extremely tolerant of disturbed and highly anthropogenic environments. Nests can be found in suburban backyards, in the main streets of major cities, and on industrial sites. Arboreal nests occur in some situations, and workers also forage on vegetation. This species may occur outside of Australia, and detailed comparison with southeast Asian and Pacific taxa in the monomorium-group (e.g. Monomorium chinense) would be desirable.

Nomenclature

 *  fieldi. Monomorium (Martia) fieldi Forel, 1910b: 30 (w.m.) AUSTRALIA. Heterick, 2001: 402 (q.). Combination in M. (Lampromyrmex): Emery, 1922e: 184. Senior synonym of donisthorpei, fraterculus, nigrius: Heterick, 2001: 401.
 * donisthorpei. Monomorium (Mitara) donisthorpei Crawley, 1915a: 134 (w.) AUSTRALIA. Combination in M. (Lampromyrmex): Emery, 1922e: 183. Junior synonym of fieldi: Heterick, 2001: 401.
 * nigrius. Monomorium (Mitara) laeve r. nigrius Forel, 1915b: 74 (w.q.) AUSTRALIA. Junior synonym of fieldi: Heterick, 2001: 401.
 * fraterculus. Monomorium (Mitara) laeve st. fraterculus Santschi, 1919a: 328, fig. 1 (w.) AUSTRALIA. Combination in M. (Lampromyrmex): Wheeler, W.M. 1927i: 140. Raised to species: Santschi, 1928e: 467. Junior synonym of fieldi: Heterick, 2001: 401.

Worker
Heterick (2001) - HML 0.89-1.37; HL 0.36-0.50; HW 0.30-0.43; CeI 74-90; SL 0.25-0.40; SI 79-97; PW 0.14-0.30 (25 measured).

Head. Head square or rectangular; vertex slightly concave; frons smooth and shining with combination of appressed setulae and erect and suberect setae. Compound eyes elliptical; (viewed from front) compound eyes set at midpoint of each side of head capsule; (viewed laterally) compound eyes set at midline of head capsule; eye moderate, eye width 0.5-1.5x greatest width of antennal scape. Antennal segments II; club three-segmented. Anteromedial clypeal margin straight or slightly emarginate, median clypeal carinae not produced as teeth or denticles. Longest lateral anterior clypeal setae long, extending beyond dorsal margin of closed mandibles. Posteromedial clypeal margin level with posterior surface of antennal fossae. Anterior tentorial pits situated nearer antennal fossae than mandibular insertions. Frontal lobes parallel straight. Venter of head capsule with elongate, basket-shaped setae in at least some individuals. Palp formula 1 ,2. Maximum number of mandibular teeth and denticles: four (basal tooth a minute denticle when present, often absent); mandibles (viewed from front) strap-like with inner and outer edges subparallel, smooth with piliferous punctures; basal tooth not enlarged; basal angle indistinct; apical and basal mandibular margins meeting in tooth or denticle.

Alitrunk. Promesonotal sculpture absent, promesonotum smooth and shining; dorsal promesonotal face evenly convex; erect and suberect promesonotal setae greater than 10; setulae decumbent and subdecumbent. Mesonotal suture absent. Metanotal groove present as distinct and deeply impressed trough between promesonotum and propodeum. Propodeal sculpture absent; propodeum smooth and shining, or present as faint microreticulation with few striae, mainly on lower lateral surface; dorsal propodeal face strongly convex to gently convex, or sloping posteriad, with wedge-shaped flattening or shallow depression that is widest between propodeal angles; processes absent (propodeum smoothly rounded in profile or with slight hump at propodeal angle); lobes absent or indistinct, or present as blunt flanges. Propodeal angle absent; declivitous face of propodeum smoothly convex to flat. Erect and suberect propodeal setae 5-10; propodeal setulae decumbent and subdecumbent. Propodeal spiracle lateral and nearer metanotal groove than declivitous face of propodeum, or lateral and about midway between metanotal groove and declivitous face of propodeum; vestibule absent or undeveloped.

Petiole and postpetiole. Petiolar spiracle lateral and in anterior sector of petiolar node. Petiolar node conical, dorsally rounded, or conical, sharply tapered, or cuneate, dorsally rounded; sculpture absent, petiolar node smooth and shining. Ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) near 4:3 to near 1: 1. Anteroventral process distinct in some individuals as slender carina that tapers posteriad. Ventral lobe always absent. Height ratio of petiole to postpetiole near 4:3 to near 2:1; height-length ratio ofpostpetiole near 2:1 to near 4:3. Sculpture absent on dorsum, at least: postpetiole smooth and shining. Ventral process absent or vestigial.

Gaster. Pilosity of first gastral tergite consisting of combination of appressed setulae and longer, erect and suberect setae.

General characters. Colour of head, alitrunk, petiole and postpetiole brown, gaster brown to black, legs cream to chocolate. Worker caste monomorphic.

Queen
Heterick (2001) - HML 1.57-3.01; HL 0.52-0.69; HW 0.46-0.69; Cel 87-100; SL 0.34-0.45; SI 74-79; PW 0.32-0.66 (7 measured).

Head. Head square or rectangular; vertex planar; frons smooth and shining with combination of incurved decumbent and subdecumbent setulae and erect and suberect setae. Compound eyes elliptical; (viewed from front) compound eyes set in anterior half of head capsule, or set at midline of head capsule; (viewed laterally) compound eyes set at midline of head capsule; eye large, eye width greater than 1.5 x greatest width of antennal scape.

Alitrunk. Mesoscutum in profile convex anteriad; thereafter flattened, or evenly flattened. Mesoscutal pilosity consisting of decumbent and subdecumbent setulae anteriad and erect and suberect setae posteriad; dorsal appearance of mesoscutum smooth and shining; length-width ratio of mesoscutum and scutellum combined near 2:1 to near 4:3. Axillae contiguous or nearly so, or separated by distance less than half greatest width of scutellum. Propodeal sculpture absent; propodeum smooth and shining; dorsal propodeal face gently convex, or flattened. Propodeal processes absent (propodeum smoothly rounded in profile or with slight hump at propodeal angle); lobes absent or indistinct. Propodeal angle absent. Erect and suberect propodeal setae greater than 10; propodeal setulae decumbent and subdecumbent. Propodeal spiracle lateral and nearer metanotal groove than declivitous face of propodeum, or lateral and about midway between metanotal groove and declivitous face of propodeum. Wing. Wing veins predominantly depigmented with distal segments reduced to vestigial lines; vein m-cu absent; vein cu-a absent.

Petiole and postpetiole. Petio1ar spiracle lateral and in anterior sector of petiolar node. Petiolar node conical, dorsally rounded, or cuneate, dorsally rounded; sculpture absent, petiolar node smooth and shining. Ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) near 4:3 to near 1: l. Anteroventral process distinct in some individuals as slender carina that tapers posteriad. Height ratio of petiole to postpetiole near 4:3; height-length ratio of postpetiole near 2: l. Sculpture absent on dorsum, at least: postpetiole smooth and shining; ventral process absent or vestigial.

Gaster. Pilosity of first gastral tergite consisting of combination of appressed setulae and longer, erect and suberect setae.

General characters. Colour brown. Brachypterous alates not seen. Ergatoid or worker-female intercastes not seen.

Male
Heterick (2001) - HML 2.14-2.57; HL 0.55-0.67; HW 0.62-0. 74; CeI 11 0-119; SL 0.16-0.21; SI 23-28; PW 0.59-0.83 (3 measured).

Head. Head width-mesoscutal width ratio near 1: 1. Compound eyes protuberant and elliptical; (viewed laterally) compound eyes set at midline of head capsule; ocelli not turreted. Ratio oflength of first funicular segment of antenna to length of second funicular segment near 2:5 to near 1:2. Maximum number of mandibular teeth and denticles: two.

Alitrunk. Mesoscutum in profile evenly convex; dorsal appearance of mesoscutum finely microreticulate; mesoscutal pilosity consisting of numerous short setae, incurved medially. Parapsidal furrows vestigial; notauli absent. Axillae separated by distance more than half greatest width of scutellum.

Wing. Wing veins predominantly depigmented with distal segments reduced to vestigial lines; vein m-cu absent; vein cu-a absent.

Petiole and postpetiole. Petiolar spiracle lateral and in anterior sector of petiolar node. Sculpture absent, petiolar node smooth and shining, or present in form of microreticulation; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) near 1:1 to near 3:4. Anteroventral process present as pronounced spur, or slender carina that tapers posteriad; ventral lobe always absent. Height-length ratio of postpetiole near 3: 1; sculpture present in form of microreticulation; ventral process absent or vestigial.

Gaster. Pilosity of first gastral tergite consisting entirely of well-spaced erect and suberect setae.

General characters. Colour chocolate to russet; legs pale yellow.