Myrmicinae

This is the largest subfamily in Australia, based on both the number of genera and the number of species. Myrmicines range greatly in size, with the smallest about 1 mm long and the largest up to 10 mm. While many species are generalist predators, some specialise on selected soft-bodied invertebrates such as Collembola and others are important seed harvesters. Workers can be found foraging at all times of the day and night, sometimes in large numbers. Nests can be found in almost any suitable location from deep in the soil to the upper branches of trees. Colonies are generally small with a few hundred to a few thousand workers, although some species can have huge nests with many thousands of workers while others form very small nests with fewer than 50 individuals.

Morphologically, these ants are very diverse. Many groups are highly modified with unusual mandibles, elongate spines, elaborate hairs or unique structures not seen in any other ants. Because of this, many genera are relatively easy to identify as they have highly distinctive features which are easily seen (given the appropriate magnification). At the same time, some genera are much less specialised or modified, and separating these from close relatives can be difficult. In these cases, close inspection of subtle differences may be required.

Myrmicines occur throughout the world in all major habitats (except arctic and antarctic regions). They are the largest subfamily of ants with over 6700 species and subspecies and 155 genera. Australia has over 350 species placed in 38 genera. Eight of the genera are restricted to Australia.

Identification
The mesosoma is attached to the gaster by two distinct segments, the petiole and postpetiole. The mandibles are generally triangular, but if they are elongate then there are no teeth along the inner margin and they are attached near the middle of the front margin of the head. The eyes are almost always present, conspicuous and with many facets but are absent in a few species. The frontal lobes are always present and expanded towards the sides so they cover the inner part of the antennal bases where they are inserted into the head when viewed from the front. The pronotum and mesonotum are fused into a single plate.

Species of myrmicines are most likely to be confused with species of Leptanilla or Tetraponera because of the two segmented petiole. However, both Leptanilla and Tetraponera have the pronotum and mesonotum unfused and with a flexible joint between them, while in all myrmicines these two plates are fused into a single structure.

Boudinot (2015) - Male Myrmicinae are uniquely identified by the strongly petiolated third abdominal segment (postpetiole), axial helcium, 1,1 maximum ventroapical tibial spur count, unvaulted abdominal tergum IV, and presence of propodeal lobes. All myrmicines lack jugal lobes and have posteriorly-situated antennal toruli, but are highly variable otherwise: mandibles fully-developed to nub-like; antenna 8–13-merous; forewing with (0)1–8 eight closed cells; and petiole sessile to long-pedunculate. Some myrmicines, e.g., Adelomyrmex and Acanthognathus, have extremely reduced wing venation similar to Leptanillinae; all myrmicine taxa examined during this study with reduced wing venation have conspicuous propodeal lobes, differentiating them easily from Leptanillinae despite secondary petiolation of abdominal segment III in some leptanillines.

Nomenclature
MYRMICINAE [subfamily of Formicidae]
 * Myrmicites Lepeletier de Saint-Fargeau, 1835 [as family-group name]: 169. Type-genus: Myrmica.
 * Myrmicidae: Smith, F. 1851: 4 [emended spelling].
 * Myrmicidae: Smith, F. 1857a: 70 [as subfamily of Formicidae].
 * Myrmicinae: Forel, 1893a: 163 [emended spelling of suffix].

Bolton 2003:

The myrmicomorph subfamilies

Subfamilies Agroecomyrmecinae, Myrmicinae.

Diagnosis Paraglossae present on labium (note 1). Antennal sockets vertical or strongly inclined upward toward midline of head (note 2). Torulus not completely fused to frontal lobe. Ocelli absent (note 3). Promesonotal suture usually absent, less commonly vestigial; in the latter case the suture is fully fused and immobile, the pronotum and mesonotum incapable of movement relative to each other (note 4). Metacoxal cavities fully closed, the annulus broad and without a suture (note 5). Propodeal lobes usually present (note 6). Waist of two segments petiole plus postpetiole) (note 7). Petiole with complete tergosternal fusion (note 8). Presclerites present on abdominal segment IV (first gastral) (also in male) the presternite distinctly shorter than the pretergite (note 9). Pretarsal claws without a preapical tooth on the inner margin (note 10). Sting present, usually functional. Jugal lobe absent from hindwing of alates. Pupae naked. [Synopsis, p. 181.]

Notes (1) Paraglossae have not been recorded in Metapone; the presence of paraglossae is regarded as plesiomorphic. (2) For distribution of character see notes under formicomorph subfamilies. In most myrmicomorphs the antennal sockets are relatively widely separated. They are secondarily approximated in tribes such as Stenammini, Solenopsidini and Melissotarsini and secondarily extremely widely separated in Agroecomyrmecini and Cataulacini. (3) Ocelli are considered absent in myrmicomorph workers although in worker polymorphic taxa, especially those with major workers that develop gyne-like characters (for example some Pheidole, Pheidologeton, Oligomyrmex, Atta, Solenopsis geminata group, some Crematogaster depressa group (list is not exhaustive) the largest may have at least a median ocellus present. Elsewhere ocelli, or more usually the median ocellus alone, may be sporadically and perhaps teratologically developed in individuals or nests (observed in Atopomyrmex, Cataulacus, Huberia, Metapone, Monomorium). Ocelli are universal in alate queens and males. (4) In some myrmicomorph taxa a line or feeble indentation across the dorsal alitrunk may indicate the original track of the pro meso notal suture. Elsewhere in the family the suture is also univerally fused and immobile in all dorylomorph subfamilies except Leptanilloidinae, and fused in the poneromorph groups Ectatommini, Paraponerini, Proceratiini and Probolomyrmecini. Plesiomorphic lack of promesonotal fusion, with retained mobility of pronotum and mesonotum relative to one another, is characteristic of the formicomorphs, myrmeciomorphs and leptanillomorphs, as well as the dorylomorph subfamily Leptanilloidinae and all poneromorphs except those mentioned above. (5) For distribution of character see notes under Dolichoderinae. (6) Propodeallobes are universal in myrmicomorphs except for Melissotarsini and some Crematogastrini, where their absence is regarded as a secondary adaptation. For distribution of this character see notes under myrmeciomorph subfamilies. (7) All myrmicomorphs have a two-segmented waist and the character probably represents a single evolutionary event. A single-segmented waist, the plesiomorphic condition, is universal in formicomorphs and poneromorphs except for Paraponerini and a few species of Proceratiini, where segment III is quite reduced and could be termed sub-postpetiolate. Among the myrmeciomorphs, dorylomorphs and leptanillomorphs both counts occur in each group and sometimes both counts occur within a single subfamily, as is the case in Myrmeciinae, Cerapachyinae and Ecitoninae. It is obvious that the reduction of abdominal segment III to a distinct postpetiole has evolved independently many times in Formicidae. (8) For distribution of character see notes under formicomorph subfamilies. (9) The relatively short presternite on abdominal segment IV is also found in Pseudomyrmecinae. This feature has almost certainly arisen independently and is not a myrmicine/pseudomyrmecine synapomorphy. (10) Pretarsal claws are also simple, lacking a preapical tooth, in the formicomorph and leptanillomorph subfamilies. In other subfamily groups such teeth are variously developed, being absent in some taxa, present in others; the presence of such teeth is plesiomorphic.

MYRMICINAE

Diagnosis. With characters of myrmicomorph subfamilies. Clypeus usually inserted between antennal sockets (note 1). Antennal sockets usually not strongly migrated laterally (note 2). Metapleural gland orifice a longitudinal slit or narrow crescent that opens dorsally to posterodorsally, not overhung by a cuticular flange or flap (note 3). ''Petiole in posterior view with the fused tergile and sternile equally convex, their inner margins forming a circle. Tergite and sternite of helcium together form a rough circle in frontal view, the apices of the two sclerites meet end to end, the tergile does not overlap the sternite''; helcium sternite bulges ventrally and is not retracted (note 4) (also in male). Abdominal segment III (postpetiole) usually without tergosternal fusion (note 5); abdominal segment IV without tergosternal fusion (note 6), with or without a stridulitrum on pretergite. Sternite of abdominal segment IV not reduced, the segment not strongly downcurved. Postpygidial glands absent (note 7). [Synopsis, p. 182.]

Notes. (1) Median portion of clypeus fails to extend back between the antennal sockets only in Melissotarsini; this is considered to be an independent apomorphic development of that tribe. (2) The only genus in which the antennal sockets and frontal lobes are strongly migrated laterally is Cataulacus, in which feature it resembles Tatuidris (see above), but otherwise their cephalic morphologies are extremely different. (3) Vertically directed guard-hairs that arise some distance below the orifice are frequently developed. External appearance of the metapleural gland is very similar to that encountered in Ectatomminae; the structure may be synapomorphic. The slit-like orifice of the gland is usually so narrow in Myrmicinae that it is inconspicuous. (4) A ventrally bulging helcium sternite is also developed throughout the dorylomorph subfamilies, in Discothyrea (Proceratiini) and in Tatuidris (Agroecomyrmecini), but in all of these the sternite is retracted, so that tergite overlaps sternite, and the latter is attached some distance up the inner surface of the tergite. (5) Tergosternal fusion of abdominal segment III occurs only in Cataulacini, Cephalotini and Myrmicaria among all the Myrmicinae. This may be a synapomorphy in the first two but is certainly independently derived in the last. For distribution of this character elsewhere in the family see notes under dorylomorph subfamilies. (6) In Ankylomyrma the tergite of abdominal segment IV is enormously hypertrophied; the sternite appears to be a small sclerite fused to the anteroventral rim of the tergite: see under Ankylomyrmini. (7) Postpygidial glands are also absent in the formicomorph subfamilies, almost certainly independently.

Comments (i) This subfamily, overwhelmingly the largest, most diverse and most successful of the Formicidae, is divided into a number of tribes, which are gathered here into formal or informal tribe groups. Some groups of tribes are demonstrably monophyletic (the dacetine-, cephalotine-, and attine tribe groups) but the remainder are grouped only by inclusive diagnoses, so their monophyly remains in doubt. Within this latter set of groups some individual tribes are demonstrably monophyletic but others are not. A number of new, mainly monogeneric, tribes have been set up to accommodate the more obvious problem areas. In general these are taxa with a wealth of autapomorphic developments but a dearth of recognisable synapomorphies. (ii) Many of the extreme inquilines (workerless permanent social parasites) encountered in the Myrmicinae will fail taxon diagnosis because of their "inquiline syndrome" habitus and grossly convergent morphological reductions and modifications, acquired in response to their unique way of life. Inclusion of such forms in higher taxa must rest upon molecular analysis, for instance the proof by Sanetra & Buschinger (2000) that the extreme inquilines Anergates and Teleutomyrmex are correctly grouped with Tetramorium. (iii) For another possible Ectatommini/Myrmicinae synapomorphy (as well as (3) above) see comments under the former.