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. Euprenolepis, Nylanderia, and Pseudolasius also have these deep and complete sutures and together form a clade with Paratrechina. 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. 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. Reproductives 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. Larvae 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. Reproductive biology While most ant species exhibit arrhenotokous parthenogenesis in which diploid, fertilized eggs become females (workers or queens), and haploid, unfertilized eggs become males, Paratrechina longicornis is one of several ant species also known to be thelytokous, and queens can additionally produce female offspring asexually. As a result, sibling mating allows recombination of alleles without increasing deleterious homozygosity and bypasses the downsides of inbreeding because the genomes of the queens and males within a colony are not linked. Symbiosis See also: Myrmecophily Mutualism 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. The ants are thought to provide protection to the caterpillars against natural enemies in return for this source