During a three year investigation in fast flowing streams of the north-eastern regions of the Himalaya (India: State Himachal Pradesh, Kullu-Valley) phoretic associations of blackflies with Heptageniidae were studied. Simulium rashidi Lewis, 1973 and Simulium ephemerophilum Rubtsov, 1947 were recorded to develop on Epeorus bispinosus Braasch, 1980, Electrogena eatoni (Kimmins, 1937), Iron martensi Braasch, 1981, Iron psi (Eaton, 1883) and Rhithrogena tianshanica Brodsky, 1930. Further small blackfly larvae were found on a not identified species of Rhithrogena. Field observation proofed that at least in S. rashidi the attachment to a carrier is not species specific. Nevertheless, laboratory experiments revealed clear preferences for Heptageniidae, especially for E. bispinosus. Although larvae of phoretic blackflies proofed to be able to reattach on another individual, this seems to be done only in case the carrier died. Moreover preferences for special body regions of the Heptageniidae were evident. While larvae preferentially localised on the thorax, most of the pupae were found on the wing area of the carriers. The development of phoretics and carriers seemed to be well synchronised, because blackfly development had been finished right before the mayfly carrier emerged.