Tetramorium immigrans

More thermophilic than all species except Tetramorium hungaricum, Tetramorium breviscapus, and Tetramorium fusciclava; TAS of 201 sites 19.9 ± 2.5 °C [13.0, 26.7]. In France and partially Central Europe synanthropic: roadsides, ruderal areas, parks, gardens, pavements, railway constructions, stone pits, balconies, inside of buildings. In Pannonian zone, Mediterranean, and Caucasus most common species in anthropogenic areas, but also primary habitats like semi-arid and arid grasslands, rocky and sandy grasslands, beaches, river banks, rock walls. Bulgarian records from forests. Nests often between cracks of concrete, asphalt, rocks, as well as under stones; small soil mounds exist.

Identification
A member of the Tetramorium caespitum complex. The species can be determined with a discriminant analysis of a set of morphological measurements. See Wagner et al. (2017) and https://webapp.uibk.ac.at/ecology/tetramorium/

Distribution
Wagner et al. (2017) - Mediterranean, Western Europe, Central Europe, Balkans, Eastern Europe, Anatolia, Caucasus, introduced to North (Steiner & al. 2008) and South America (Santschi 1927).

Distribution based on Regional Taxon Lists
Nearctic Region: United States. Neotropical Region: Argentina, Chile. Palaearctic Region: Bulgaria, Turkey.

Biology
In North America, this species is a common indoor pest in eastern North America, especially near the coast. Nests are frequently located under building foundations and workers forage for food inside. Once a food source is located, mass recruitment occurs along a well defined odor trail. Commonly known as "pavement" ants this species is often seen in late spring and early summer out on sidewalks in huge battles with neighboring colonies. Baits can be very effective in eliminating colonies within structures. In nature, colonies are often found nesting in soil under stones and the eastern subterranean termite is a common prey.

Adult sexuals on 27 June ± 39d [17 March, 29 September] (n = 16). Tetramorium atratulum was found in a nest of Tetramorium immigrans (Wagner et al. 2017).

Hybridizes with Tetramorium caespitum (Wagner et al. 2017; Cordonnier et al. 2019; Cordonnier et al. 2020).

M.R. Smith (1956) - Nests are usually constructed in exposed soil, or under the cover of stones, pavement, or other objects, and in rotting wood ... also in houses, most commonly around or between the lower masonry walls of the foundation .... Colonies are moderately large to large .... The ants are almost omnivorous and feed on both dead and live insects, honeydew, seeds, the sap of plants, and various household foods such as meats, grease, nuts, potato chips, cheese, honey and bread, but the ants seem to show a preference for meat or grease. Workers steal seeds from seed beds and girdle, scar, or scarify the roots or stems of many agricultural plants.

Sano et al. (2018) characterized the cuticular hydrocarbons of this species. They also showed that workers use cuticular hydrocarbon profiles to recognize non-nestmate conspecific and heterospecfic workers.

Nomenclature

 *  immigrans. Tetramorium caespitum var. immigrans Santschi, 1927a: 54 (w.) CHILE.
 * Junior synonym of caespitum: Bolton, 1979: 171; Radchenko, 2016: 244.
 * Status as species: Wagner, et al. 2017: 120 (redescription).

Worker
Wagner et al. (2017) - Lectotype in μm: CL = 914, CW = 912, dAN = 246, EL = 183, EW = 142, FL = 355, HFL = 783, MC1TG = 25.1, ML = 1100, MPPL = 318, MPSP = 427, MPST = 236, MtpW = 461, MW = 592, PEH = 313, PEL = 218, PEW = 310, PLSP = 223, PLST = 243, PnHL = 238, PoOc = 363, POTCos = 12, PPH = 343, PPL = 144, Ppss = 68, PPW = 379, PreOc = 223, RTI = 359, SLd = 727, SPST = 213, SPWI = 289.

Largest species of complex, CS = 834 ± 56 [713, 943] μm. Dark brown to blackish, rarely reddish.

Head moderately elongate, CL / CW = 1.012 ± 0.013 [0.985, 1.035]. Eye medium-sized, EYE / CS = 0.176 ± 0.004 [0.167, 0.189]. Scape long, SLd / CS = 0.784 ± 0.014 [0.755, 0.817]. Mesosoma moderately long and narrow, ML / CS = 1.158 ± 0.020 [1.109, 1.201], MW / CS = 0.629 ± 0.012 [0.605, 0.649].

Promesonotal dorsum convex, metanotal groove shallow. – Head dorsum and occiput with longitudinal costae and costulae. Postoculo-temporal area of head with highest number of costae and costulae in complex, POTCos = 12.33 ± 1.67 [8.25, 16.13]. Mesosoma dorsum longitudinally rugulose, lateral side of propodeum with pronounced sculpture, Ppss = 30.5 ± 14.5 [13.6, 63.3]. Dorsum of petiolar with sculpture, reticulate microsculpture, or smooth. General surface appearance rather dull. – Connected stickman-like or reticulate microsculpture: large units scattered over 1st gastral tergite, MC1TG = 21.67 ± 2.68 [16.07, 27.00]. – Some workers with long c-shaped, crinkly, or sinuous hairs on ventral head posterior to buccal cavity.

Male
Wagner et al. (2017) - Paramere structure belongs to caespitum-like form: ventral paramere lobe with one or two sharp corners; without distinct emargination between paramere lobes in posterior view, both paramere lobes reduced in size. In ventro-posterior view, second corner on ventral paramere lobe > 87 μm apart from first. In posterior view, two corners on ventral lobe.

Type Material
Wagner et al. (2017) - Valparaíso (Chile), 33.05° S, 71.61° W, 18 m, leg. Edwards, 1926. Lectotype designation. Worker of middle card closer to needle than second worker, labeled "TYPE [–] "Chili Valparaiso, Miss Edwards" [–] "Tetramorium caespitum L immigrans Sant". SANTSCHI det. 19 "26" [–] Sammlung Dr. F. Santschi Kairouan", designated as lectotype. Lectotype worker and seven paralectotype workers in Naturhistorisches Museum Basel (Switzerland).