A faunal survey of spring habitats in rangeland springs in central Oregon yielded a new species of water mite in the genus Arrenurus (Hydrachnidae: Arrenuridae). Through a combination of field collections and laboratory rearing the larva, deutonymph, male and female were associated and described. Arrenurus (Arrenurus) hamrumi, sp. nov. parasitizes adults of the damselfly Argia vivida Hagen, which is a common damselfly in springs, but heretofore has not been reported to be parasitized by water mite larvae. A. hamrumi closely resembles A. harperae Cook, which is known from springs in New Mexico and Arizona. These two species, along with A. texensis Young, A. arizonensis Cook, and A. tamaulipensis Cramer and Cook belong to a distinctive species group that is known only from spring and lotic habitats in the western Unites States and a lake in northern Mexico.
- Argia vivida