Members of the Holarctic genus Sperchon Kramer are among the most common and widespread water mites in lotic habitats. Approximately 225 species and subspecies of Sperchon have been described worldwide (Viets 1987), and about 25 of them have been reported from North America (Habeeb 1967). Smith and Cook (1991) estimate that over 100 species, mostly undescribed, occur in the Nearctic region. Adults and deutonymphs of this genus are free-living predators (Smith and Oliver 1986; Proctor and Pritchard 1989). Larval Sperchon are typically parasites of adult nematocerous Diptera, especially Chironomidae (Smith 1982; Smith and Oliver 1976, 1986) and Simuliidae (Davies 1959; Smith and Oliver 1986), but have also been reported to use certain Trichoptera as hosts (Smith and Oliver 1986). Larvae of Sperchon are initially aquatic, and actively crawl or swim to locate the prepupae or pupae of appropriate hosts. They transfer to host adults during ecdysis, embed their chelicerae in host tissue, and engorge rapidly, often within a few hours, on fluids before dropping off the host and into the water where the life cycle continues. Larvae preferentially select attachment sites on the thorax of hosts, but can utilize sites on the anterior segments of the abdomen when thoracic sites are already occupied. Most larval Sperchon are evidently specialized to parasitize hosts whose immature stages inhabit stenothermal, lotic habitats. We report here on the first records of larval Sperchon parasitic on mountain midges.