A total of 257966 specimens from 149 catches of drosophilid flies from Switzerland, belonging to the 34 most frequent species are considered here. The records are screened for effects of environmental factors (geographical region, altitude, season, habitat, soil, climate) on the size and diversity of the samples. Furthermore, the individual species are compared with respect to frequency and diversity, and to the effect of the above factors on their proportions in the samples. Fig. 1. Localities in Switzerland (for code numbers see Table 1) from which a total of 149 samples was collected. Regions are abbreviated as follows: J = Jura, M = Mittelland (dotted), P = Prealps, A = Alps (dotted), T = Ticino u. S.