1. Community patterns are generated by multiple processes and constraints generated at different spatial and temporal scales. 2. A large-scale study was carried out on the Trichoptera of four Algerian regions with contrasting climates, vegetation cover, and human pressures. 3. Overall, 22 identified taxa were recorded, including nine families and 14 genera. The genus Hydropsyche was represented by eight species, with Hydropsyche maroccana and Hydropsyche lobata being the most abundant species. 4. With one exception, localities in the subhumid Collo and the high-altitude Batna were the most species rich, whereas localities in the semi-arid Oum el Bouaghi were the most species poor. 5. Nonmetric multidimensional scaling (NMDS) separated the caddisflies recorded into four assemblages organized by a set of constraining environmental factors (land use, altitude, water depth, helophyte cover, and flow velocity gradients) acting at different scales.6. As inadequate knowledge of insect biodiversity is a major limitation to their conservation, this article discusses how these results might help predict caddisfly communities in adjacent regions and enhance conservation efforts.