Tetramorium immigrans

The pavement ant is dark brown to blackish, and long. A colony is composed of workers, alates, drones (male ants), and a queen. Workers do have a small stinger, which can cause mild discomfort in humans but is essentially harmless. Alates, or new queen ants and drones, have wings, and are at least twice as large as the workers. Tetramorium nuptial flights occur in spring and summer; queens and drones leave the nest and find a mate. The drone's only job is to mate with the virgin queens. The dealate, or newly fertilized queen, sheds her wings, finds a suitable nesting location and digs a founding chamber called the clausteral chamber or cell. The queen must raise the first generation of young herself until they are old enough to forage for food. During this period she survives by metabolizing the proteins of her flight muscles. As the eggs hatch and the ants develop, they spend that time, about two to three months, tending to the queen of their colony; they will continue helping in the colony until they are a month old. Older workers forage for food and defend the colony. They will eat almost anything, including other insects, seeds, honeydew, honey, bread, meats, nuts, ice cream, and cheese. Although they do not usually nest inside buildings, they may become a minor nuisance to humans as they enter homes, attracted by food left out. They are also predators of codling moth larvae. ==Habitat and nests==

Tetramorium immigrans creates nests that are shallow to moderately deep in pavement cracks, compacted soil, and other disturbed urban substrates. Multiple surveys have indicated that the nests occupy a surface area of between 1.2-4.8 m², with workers defending a surrounding area of approximately 43 m², but there is variation observed throughout colonies that are outside of this bracket. In certain soils, shafts and isolated chambers may reach up to 60-90 cm in depth. Nests will frequently exhibit multiple entrance points that are characterized by crater-like mounds of excavated soil, which become particularly prominent in the warmer season during periods of increasing foraging. Colony size and inter-colony interactions Colonies of T. immigrans are relatively large when compared to the colonies of similar temperate ant species. Field observations have commonly reported colony sizes that range from a few thousand workers to over 10,000 individuals in nests that have been well-established. Rapid growth is possible for nests in the first 1-2 years of a colony being founded. A colony can be started by a single queen that is responsible for all reproduction for the lifetime of her colony. In some cases nests may occasionally have two or more queens. Recent observations have recorded complex interference behaviors during fights that include soil-dropping (blocking exits/entrances of rival nests using small debris) as a way to hinder the foraging of neighboring colonies. Colony recognition and the decision to fight are mediated via nestmate-recognition cues so that workers may respond aggressively to non-nestmates carrying different chemical signatures that do not belong to their nest. ==Parasite==

T. immigrans serves as host to the ectoparasitic and workerless Tetramorium inquilinum ant. This parasitic ant spends its life clinging to the back of a pavement ant, particularly queens. == Urban ecology ==

Urban distribution T. immigrans prefers to settle in places with little to no vegetation. They are one of the few ant species that are seen to have a resurgence in population size after extensive urban development. Studies on ant diversity medians in New York City have found T. immigrans to be the most populous ant species, at upwards of 93%. They have been said to be established in approximately 39 states in the mainland U.S. and also 3 Canadian provinces. Their expansion increases readily across North America yearly. Urban heat and physiological adaptations Tetramorium immigrans is tolerant of high surface temperatures that are representative of urban areas. Measurements of individuals sampled from an urban microhabitat in South Dakota observed worker ants alive at temperatures close to 46 °C. Studies of related ant species in similar urban habitats showed that prolonged exposure to city heat-island conditions lead to an increased thermal tolerance compared to rural colonies, demonstrating heat as a potential selective pressure on physiology. Individuals with traits that favor heat tolerance are more likely to survive and reproduce, forming colonies that are uniformly resistant to urban heat. Surface temperatures in urban habitats also influence community structure and biodiversity. Surveys collected across multiple North American cities show that warmer and impervious urban landscapes support lower overall diversity, yet they favor heat and disturbance-tolerant species such as T. immigrans. This reduction in biodiversity may further reinforce the dominance of heat-adapted ants, and, over time, the effects of temperature-driven selection and simplified urban communities promotes adaptations that enhance T. immigrans’ success in warm, paved, and impervious environments. Additional observations show that T.immigrans exploits any food or nutrient source that can be found. When a source of food is discovered, a worker can quickly recruit other workers to the source of food far faster than any other competing native ant species. Urbanization also has a major impact on influencing the community structures in T. immigrans. When studied across urban gradients, T. immigrans is found to be disproportionately associated with impervious areas such as pavements and sidewalks that are characteristic of urban microhabitats. T. immigrans abundance increases with the level of urbanization that can be found in a given area, which is in contrast with its close neighbors in the same area. Closely related ant species will tend to decrease in abundance and favor less disturbed areas that have not been subject to urbanization. This pattern demonstrates the dominance of T. immigrans in the impervious microhabitats that urbanization and human activity create, as other closely related ant species cannot tolerate the same conditions. Genetic testing has also uncovered distinct genetic T. immigrans sub-clusters in distant locations. These sub-clusters, when tested, appeared to be unexpectedly genetically similar even though theoretically it should be the opposite. This indicates possible accidental human-mediated dispersal, which has inadvertently expanded the species's range. Human disturbance modifies evolutionary landscapes, creating novel selective pressures and more opportunities for gene flow. With more gene flow comes new alleles, which better help T. immigrans adapt to urban environments. Additionally, T. immigrans in North America have been found to have exceptionally low levels of genetic diversity, with researchers speculating they descend from a similar lineage around two centuries ago. However, there is no detection of inbreeding amongst the species, which is a typical attribute for an invasive ant species. ==Systematics==

Tetramorium immigrans is a member of the Tetramorium caespitum complex, which includes 10 species of the genus: • Tetramorium alpestre Steiner, Schlick-Steiner & Seifert, 2010 • Tetramorium breviscapus Wagner et al., 2017 • Tetramorium caespitum (Linnaeus, 1758) • Tetramorium caucasicum Wagner et al., 2017 • Tetramorium fusciclava Consani & Zangheri, 1952 • Tetramorium hungaricum Röszler, 1935 • Tetramorium immigrans Santschi, 1927 • Tetramorium impurum (Foerster, 1850) • Tetramorium indocile Santschi, 1927 • Tetramorium staerckei Kratochvíl, 1944 These species are native to Europe. In addition, Tetramorium immigrans is common and widespread in North America. The low genetic diversity of Tetramorium immigrans across North America suggests that this population resulted from the establishment of one single, or a few closely related ant colonies, about 200 years ago. The North American species of the pavement ants has formerly been considered Tetramorium caespitum, the subspecies Tetramorium caespitum immigrans, and species E. In 2017, the Tetramorium caespitum complex was revised, and the pavement ant commonly found in North America was determined to be Tetramorium immigrans. The species is also found in southern Europe, where it originated. == Notes ==