Limnomermis steineri n. sp. (Nematoda: Mermithidae) is described from the hemocoel of male, female, and intersex imagos of Ablabesmyia (s. str.) monilis (L.) eclosing from Lake Ozawindib and Lake Alice Bog in northern Minnesota during summers 2000–2005. The species is distinguished from other described members of the genus. Paramermis rosea is returned to Limnomermis. A review of adequately described members of the genus is included. One species of the genus has been reported previously from the Nearctic Realm. Emphasis is placed on the need for host identification, larger number of specimens of both mermithid sexes, and information on the intensity of infections to enable more precise range comparisons in mermithid biometrics.