Explanation:
They are Aggressive
The pavement ant, Tetramorium caespitum L. is one of the most commonly encountered ants in the United States. The first introduction into the United States occurred from Europe in the beginning of the 19th century. Since then, the ant has become well established and is prevalent in urban areas in the northern U.S. and parts of Canada. While the presence of pavement ants in the U.S. has been acknowledged for decades, the extent of their invasiveness and severity as a pest is not well characterized.
Biology and Behavior
Reproduction and Development
Pavement ants form large colonies, often containing over 10,000 workers. As with most ants, there are distinct castes: one or a few reproductive queens, and a large number of non-reproductive female workers. In early summer, winged reproductive females and males are produced. Mating occurs during nuptial flights in which alate (winged) reproductive ants leave colonies and mate in swarms. Generally, one sex predominates in the reproductives produced by a specific nest of pavement ants (Bruder and Gupta 1972). It takes 42-63 days (at 21-24°C) for a fertilized egg to develop into a worker pavement ant in an established colony, although worker development occurs faster when a queen first starts a new colony (Bruder and Gupta 1972).
Colonies of Tetramorium caespitum are usually monogynous - they are started by a single reproductive queen that carries out all reproduction for the lifetime of that colony - but they occasionally may have two, or possibly more, queens. The majority of nests occupy 1.2-4.8 m2 in area and are 0.45-0.90 m deep (Bruder and Gupta 1972), with multiple crater-shaped mound entrances per nest. Mounds near entrances are not always obvious, as they are built up after rains but slowly collapse thereafter.
Foraging and Fighting
Workers recruit nestmates to a discovered food source through the use of pheromones. This allows for large groups of workers to process bulky food items and bring them back to the colony. Direct homing has been documented in worker ants of Tetramorium caespitum returning to the colony with food. Based on a reference light source and an awareness of the direction and distance they have traveled, Tetramorium caespitum can calculate a direct, straight-line path back to their colony while carrying food (Shen et al. 1998), making them very efficient foragers. Pavement ants are generalists and their diet includes arthropods, honeydew, seeds, and pollen. The average area over which a colony of Tetramorium caespitum maintains a territory in its native range was estimated to be 43 m2 (Brian et al. 1967).
In its introduced range, Tetramorium caespitum thrives in human-modified environments. In surveys of urban environments where pavement ants are found, they generally account for most ants found at baits and around residences (Buczkowski and Richmond 2012). These ants are also very resilient, being one of only a few species of ants found to recolonize an area after intensive human development, such as construction projects (Buczkowski and Richmond 2012).
Economic Importance
Pavement ants are often considered invaders of homes because sidewalks, walkways, and patios make ideal habitat for these animals. However, it remains unclear whether these ants can infest homes with damaging consequences or whether inquisitive workers just become aesthetic pests when they make it into residences or are abundant on a patio. One record suggests that Tetramorium caespitum can be troublesome because they defend agricultural aphid pests (Merickel and Clark 1994), although pavement ants are less protective of aphids than other common ants (Katayama and Suzuki 2003). In Kentucky, Tetramorium caesptium have been documented to build protective structures made of soil around magnolia scale insects, significantly lowering the number of scales parasitized by flies and increasing damage to these plants (Vanek and Potter 2010). Ecologically, pavement ants may competitively exclude native ants from urban environments (Lessard and Buddle 2005).
Although Tetramorium caespitum is an introduced species, it may be beneficial in some scenarios. One example would be the potential for this ant to keep out more damaging ant invaders. In laboratory experiments, workers from colonies of Tetramorium caespitum destroyed recently founded colonies of the red imported fire ant, Solenopsis invicta (King and Phillips 1992). Such conflict in nature may help impede the northern expansion of fire ants. The pavement ant may also be an important ecosystem service provider in urban environments, by dispersing seeds, aerating soil, and recycling nutrients.
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