Tetramorium impressum

Tetramorium impressum is common in newly rehabilitated sand mines in WA (pers. obs.; also mentioned but not named in Bisevac and Majer 1999) where it may collect seeds of grasses or herbs. This species is much less abundant in sites representing later successional stages. (Heterick 2009)

Identification
Heterick (2009) - Tetramorium impressum probably should be regarded as a species complex. Workers with black foreparts, yellow gaster and deeply impressed striae may well be genetically distinct from those that are reddish and more finely striate. However, the sculpture and shape of the node are identical in the two groups. Both forms also key out at ''T. impressum using Bolton’s (1977) taxonomic key to Australian Tetramorium'' species. All are widespread throughout the SWBP, WA.

Bolton (1977) - This is one species which I strongly suspect may be a composite, with more than one sibling species concealed in it. The variation in size, development of frontal carinae and antennal scrobes, and the variation of sculptural intensity all suggest that this species needs closer attention than I can give it at the present time. The holotype of impressum lies at the lower end of the size range given above.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  impressum. Xiphomyrmex impressus Viehmeyer, 1925a: 30 (w.) AUSTRALIA. Combination in Tetramorium: Bolton, 1977: 138.

Worker
Bolton (1977) - TL 2.9-4.1, HL 0.76-1.02, HW 0.72-1.00, CI 92-98, SL 0.52-0.68, SI 69-77, PW 0.54-0.72, AL 0.90-1.22 (15 measured).

Mandibles with varying sculpture, usually weakly striate but more rarely almost smooth. Frontal carinae weak and short, the anterior portion with a narrow, raised flange which extends back to the level of the eyes at most. Behind the level of the eyes the frontal carinae are absent or are in no way separable from the remainder of the cephalic sculpture. Antennal scrobes shallow and very weak or virtually absent, in larger individuals much less distinct than in smaller. Propodeal spines stout and acute, the metapleural lobes acute, elongate-triangular in shape. Petiole in profile relatively high and narrow (Fig. 69), with the dorsal length less than the height of the tergal portion of the node. Dorsal head finely and usually quite regularly longitudinally rugulose, the spaces between rugulae reticulate-punctate. Dorsal alitrunk predominantly longitudinally rugulose but with some cross-meshes, which are usually conspicuous on the pronotum. Spaces between rugulae punctate. Dorsal surfaces of petiole and post petiole coarsely sculptured with a mixture of rugosity and puncturation, the base of the first gastral tergite often feebly reticulate or punctulate but smooth in some specimens. All dorsal surfaces of head and body with numerous erect or suberect hairs. Colour ranging from yellow-brown to mid-brown, usually with the gaster lighter in shade than the alitrunk.

Taxonomic Notes
Heterick (2009) suggests that T. impressum may include two separate species: one with black foreparts, a yellow gaster and deeply impressed striae, and another reddish form that is more finely striate.

References based on Global Ant Biodiversity Informatics

 * Bolton B. 1977. The ant tribe Tetramoriini (Hymenoptera: Formicidae). The genus Tetramorium Mayr in the Oriental and Indo-Australian regions, and in Australia. Bulletin of the British Museum (Natural History). Entomology 36:67-151.
 * Callan S. K., and J. D. Majer. 2009. Impact of an incursion of African Big-Headed ants, Pheidole megacephala (Fabricius), in urban bushland in Perth, Western Australia. Pacific Conservation Biology 15(2): 102-115.
 * Chong C-S., L. J. Thomson, and A. A. Hoffmann. 2011. High diversity of ants in Australian vineyards. Australian Journal of Entomology 50: 7-21.
 * Heterick B. E. 2009. A guide to the ants of south-western Australia. Records of the Western Australian Museum Supplement 76: 1-206.
 * Taylor R. W. 1987. A checklist of the ants of Australia, New Caledonia and New Zealand (Hymenoptera: Formicidae). CSIRO (Commonwealth Scientific and Industrial Research Organization) Division of Entomology Report 41: 1-92.