Abstract
1. In order to investigate the feeding behaviour of the simuliid larvae, they were collected with polyvinyl-tape traps at a branch of Sagamigawa River, the northern part of Kanagawa prefecture, from August 1974 to May 1975 and the compositions of diatom flora in their digestive tracts were compared with those in the stream water, on the rock surface and on the polyvinyl-tape traps in the stream. 2. A great similarity of the diatom flora was found among the simuliid larvae of different species collected at the same location and time. 3. A great similarity was found between the samples collected from the rock surface and those from the stream water. 4. A great similarity of the diatom flora was also found among the digestive tracts, the rock surface and the stream water. Whereas, little similarity was found between the floras of the digestive tracts and polyvinyl-tape traps on which the simuliid larvae attached eventually. 5. It is concluded that the simuliid larvae feed on materials drifting (suspending) in the stream rather than those attaching on rocks.
