Paratrechina

Paratrechina species are most readily recognized by their gracile appearance due to their elongate scapes (first antennal segment), head, tibiae, and mesosoma. They also have erect macrosetae on the pronotum and mesonotum, but not the propodeum.[2][3] The mesonotal and metanotal sutures of the mesosoma are always deep and complete, dividing those parts of the body into distinct segments. These sutures are useful for distinguishing Paratrechina from three other closely related genera: Paraparatrechina, Prenolepis, and Zatania.[4] Euprenolepis, Nylanderia, and Pseudolasius also have these deep and complete sutures and together form a clade with Paratrechina.[6] Paratrechina species are very similar in appearance to those of Nylanderia, but may be distinguished by the placement of the compound eyes on the head. Nylanderia always have eyes placed to the anterior of the midline of the head, while the eyes of Paratrechina species (except Paratrechina umbra, which also has anteriorly placed eyes) are placed slightly posterior to the midline.[4] Nylanderia are also known to always have six teeth on the masticatory margin of the mandible, while most Paratrechina species have five; exceptions being Paratrechina kohli, which has eight, and Paratrechina umbra, which has six.[3][4][7]

Paratrechina queens and males are known only from Paratrechina longicornis and have not been described for any other species within the genus. The males of Paratrechina longicornis are quite distinct from those of closely related genera. Compared to those of Prenolepis and Zatania, males of Paratrechina longicornis have much shorter, more robust parameres. The parameres also have a more dorsal orientation and curvature, making them especially unique among Prenolepis genus-group males.[2][3]

In comparison with larvae of Nylanderia species, those of Paratrechina longicornis in the corresponding instars generally appear to be smaller in overall body size. Larvae of Paratrechina longicornis also show little variation in mandible shape and high variation in head setation patterns.[8]

Some species of Paratrechina have been reported to engage in mutualistic association with caterpillars of Eurybia elvina, a metalmark butterfly. The ants are attracted to the tentacle nectary organ of the caterpillars, which produces exudates rich in sugar and amino acids.[11] The ants are thought to provide protection to the caterpillars against natural enemies in return for this source of nutrition. However, it is important to note that this observation was made in 1987, long before major taxonomic changes to the genus in 2010. The publication that describes this mutualistic behavior does not specify which Paratrechina species engaged in this behavior, and the only Paratrechina species currently known from Mexico, where this behavior was documented, is the exotic pest, the longhorn crazy ant (Paratrechina longicornis.). All other species in Mexico that were thought to be Paratrechina at the time of this publication (1987) are now classified as Nylanderia species.[6] While it is possible that at least one of the species tending Eurybia elvina was Paratrechina longicornis, this is impossible to confirm from the original publication.[11]

Twenty-seven genera of Actinomycetota have been found in association with Paratrechina longicornis colonies and the soils surrounding their nests. These microorganisms often provide benefits to insects by protecting them from pathogens.[12]

Myrmecophilous, kleptoparasitic ant crickets of the species Myrmecophilus americanus are closely associated with Paratrechina longicornis nests from localities in tropics all around the world. Ant crickets live inside of ant nests and steal food resources, presumably through trophallaxis with worker ants. All known cases of ants in association with this ant cricket except one involve Paratrechina longicornis as the host ant species. The body of Myrmecophilus americanus is similar in overall size and shape to the gaster of Paratrechina longicornis queens, indicating that this may be a form of mimicry that reduces the chances that the cricket will be detected within the colony.[13]