Johnstoniana errans (Johnston) (Acari: Parasitengonae) inhabits the margins of limnic waters in forested areas. The active instars, deutonymph and adult, are nocturnal and found mainly in wet moss covering rotting wood where they prey predominantly on larvae and pupae of Diptera. The larvae, which exclusively parasitize adults of Tipula spp., recognize and rest on the pupa. When the fly emerges from the pupa, the larvae transfer to the fly and begin to feed. The life-cycle of J. errans is usually semiunivoltine, some females may reproduce more than once. Females and the obligatory diapausing eggs are the usually hibernating instars.