SUMMARY. 1. Adult Trichoptera were caught during 3 years (1980–82) in the ‘Ritrodat’ research area of the Upper Lunzer Seebach. a mountain brook near Lunz. Lower Austria, using a set of thirty pyramid type emergence traps. During the three collecting periods (112 collecting days) a total of 1810 specimens were caught. The most abundant species were Micrasema minimum McL. (Brachycentridae). Rhyacophila vulgaris Pictet (Rhyacophilidae), and the three Iimnephilid species Potamophylax cingulatus Steph., Allogamus auricollis Pictet and Ecclisopteryx guttulata Pictet.

2. In six species (Micrasema minimum, Rhyacophila vulgaris, Atlogamus auricollis, Ecclisopteryx guttulata, Drusus biguttatus Pictet, Chaetopteryx fusca Brauer) the sex ratio was significantly different from 1:1. In Micrasema minimum 422 females were caught but only three males.

3. In each year there were peaks in total emergence in early summer and early autumn.

4. The length of the emergence period of the most abundant species ranged from 38 days in Micrasema minimum to 210 days in Rhyacophila vulgaris (mean values 1980–82); there was also a difference in the intensity of emergence in these species: the percentage of time required for 50% of the animals to emerge (0%=onset of emergence, 100%= emergence completed) was 16% in Allogamus auricollis but 71% in Rhyacophila vulgaris (mean percentages 1980–82).

5. The distribution pattern of individuals per trap was tested against a Poisson distribution; in all three years the distribution was contagious.

6. The dry weight of specimens of Drusus biguttatus, Micrasema minimum. Ecclisopteryx guttulata and Wormaldia copiosa McL. was measured and. together with published dry weight values of other species (Malicky, 1976), these data were used to estimate the biomass emerging annually of twenty-three species of Trichoptera (99.2% of emergence, 1980–82). This was equivalent to 35.3 kJ m−2 in 1981 and 32.5 kJ m−2 in 1982.