We investigated the density and taxonomic composition of benthic insects in a 300 m section of riffle / pool habitat in the Shinano River, Japan. The most abundant taxa were Chironomidae, followed by Trichoptera. The total density of caddisflies and their contribution to the total density of benthic insects ranged from 56 to 21,744 (mean 11,644) ind. m-2 and from 2.6 to 44.6 (mean 29.4) %, respectively. We conducted a canonical correspondence analysis using current velocity, depth, and the ash-free dry mass of epilithon as the main factors. Benthic insect assemblages were significantly associated with the longitudinal gradient of the riffle/ pool structure. Stenopsyche marmorata and hydropsychid species were abundant in the riffles whereas Psychomyia acutipennis were abundant in the pools.Article環動昆.22(1):17-22(2011)journal articl