Monomorium rothsteini species group

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Sparks et. al. (2015) revised the Australian M. rothsteini complex. This page is based entirely on this study. To maintain consistency with the Monomorium species-groups created by Bolton (1987) and Heterick (2006) the "complex" is referred to here and in other related pages as a species-group.

There is a key for the M. rothsteini species-group: Key to Monomorium rothsteini species complex

Heterick (2001) revised the entire Australian Monomorium fauna but treated Monomorium rothsteini as a widespread, variable species. Heterick's Australian Monomoriumspecies-groups are detailed here: Australian Monomorium species-groups.



Worker (n=201). HW 0.62–1.05, HL 0.68–1.03, EL 0.14–0.22, PMH 0.23–0.49, PH 0.21–0.41, PNH 0.14–0.35, LHW 0.39–0.62, EW 0.1–0.14, PML 0.66–0.7, ML 0.64–1.17, PL 0.27–0.55, PNWdv 0.16–0.35. Head: Shape appearing square or rectangular but always longer than wide; posterior cephalic margin in full face view straight to mildly concave or broadly v-shaped, antennae 12-segmented with a well differentiated 3- segmented club; scape reaching approximately three quarters of the way to vertexal margin of head; mandible with three teeth; anterior margin of clypeus mildly to deeply concave; coarse strigae present laterally between mandibular articulation and eye; strigae may be present on frons above antennal lobes or restricted to antennal lobes or area in between; eye oval in shape, ventral margin flattened.

Mesosoma: Pronotum rounded in lateral profile, promesonotal suture clearly present, faint, or absent, posterior mesonotum slightly raised or flat; metanotal groove shallow or deeply impressed, porcate; mesonotum coarsely strigate, punctuate, both, or smooth. Propodeum with or without a raised anterodorsal transverse carina, dorsal margin in lateral view rounded, flat or sloping posteriorly, dorsal surface concave or flat to slightly rounded, with or without longitudinal carinae and transverse strigae, posterior surface near vertical or sloping. Petiole node broad to narrow and rounded dorsally, postpetiole rounded, approximately three quarters the height of the petiole. Mesopleuron and propodeum coarsely alveolate with fine to coarse striations; metanotal groove always with numerous transverse ridges; petiole without sculpture or with fine reticulation, postpetiole almost always finely reticulate; very fine reticulation present or absent on first metasomal segment.

Pilosity sparse with long and short erect or appressed white or yellow setae on head; always with one pair of elongate, inwardly curved setae arising from centre of clypeal lateral carinae, and one pair of elongate erect setae arising from antennal lobes; erect setae on vertex curved anteriorly, setae on dorsal surface of pronotum inwardly curved, elongate erect setae on propodeum curved anteriorly, erect setae on petiole and postpetiole curved posteriorly.

Colour variable; head and mesosoma amber orange, dark orange brown, dark brown or almost black; metasoma almost always dark brown to black, rarely light brown or amber, cuticle with a high gloss on non-sculptured areas.


Members of the M. rothsteini species group can be distinguished from all other species in the genus by the presence of a 12 segmented antenna, mandible with three teeth, mildly to deeply concave anterodorsal clypeal margin and alveolate sculpture on the meso- and metapleuron. Members of the M. rothsteini species group bear a close morphological relationship to M. sordidum but can be easily distinguished by the shape of the anterior clypeal margin, which is rounded in the latter (Monomorium sordidum is not granivorous).

Species in the M. rothsteini species group are a common and abundant component of the ant fauna throughout most of the Australian mainland outside mesic forests. They are predominantly seed harvesters and the nests of many of the species described here, particular the larger species that occur in the arid and northern monsoonal zones, are easily recognised by the dense middens of mostly grass seed husks that have been discarded to one side of the nest entrance. Worker ants carrying a variety of seeds and arthropod material can be observed foraging in long columns that radiate out from these nest entrances. The nests of smaller species that occur both in the northern monsoonal zone and the central and southern arid zones are less distinctive, with smaller nest middens or no obvious midden at all and with fewer workers. In many areas, the nest of one species with a large midden occurs within metres of another species with no nest midden. Although seeds appear to make up the bulk of the diet of the group generally, species are opportunistic feeders on other food sources, and it is possible that seeds are only a minor component of the diets of some species. For example, one of us (KSS) has observed several colonies of M. speculum in a dry lake bed. There was very little vegetation within foraging distance and all workers moving around the nest entrance were carrying minute gastropod shells. Workers of M. subapterum have been observed feeding on the nectar of Melaleuca flowers.

Queens and males are rarely seen. Both are rare in collections and during two extensive field trips and several shorter excursions queens and males were each observed on only one occasion. There are published accounts of species in the M. rothsteini group having brachypterous queens. Briese (1983) observed 63 queens with poorly developed wings and orange gasters emerging from a colony that subsequently underwent colony fission. The colony was within 5 m of another colony that later produced queens described as fully winged with dark brown gasters. Wheeler’s (1917) erection of M. subapterum and M. subapterum var. bogischi is based on queens he received from the South Australian Museum that had been collected from Harding River in northwest Western Australia and Port Wakefield in southern South Australia. He described these specimens as being smaller than the queens of M. rothsteini var. humilior and having very small wings. He alluded to other specific differences but did not discuss them. The lead author has examined queens from both these series in the South Australian Museum that were dealate, having just the remains of both pairs of wings and resembling fully developed queens in all other aspects. Queens that were excavated from a nest in Birdsville in southwest Queensland and here attributed to M. bogischi were all dealate with obvious wing remnants. Wheeler may have had access to other specimens than those currently available at the South Australian Museum, but based on our observations of specimens collected in the field and examined in collections, we cannot confirm brachyptery exists in this group. Larger workers that appeared to bear some aberrant characteristics (overall larger size, well defined promesonotal suture and coarser sculpture) were found foraging with other workers from a colony of M. pilbara and small, black, heavily sculptured workers have been observed foraging alongside workers of M. topend that are typically large and amber orange in colour.

Whether these aberrant forms represent an intercaste, a developmental anomaly or an apterous female is unknown.

A number of morphospecies within the M. rothsteini species group have been the subject of ecological studies.

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