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Life cycles of Rhyacophila fasciata Hagen, 1859 and Hydropsyche saxonica McLachlan, 1884 were investigated in a Dinaric karst river system. Benthic samples were taken monthly from January to December 2005. Environmental variables were measured simultaneously. Larval stages were defined using head capsule widths. As only instars 2–5 were collected in the field, the head width of first instar larvae was extrapolated using Dyar's rule. R. fasciata showed an extended emergence and recruitment, whereas in H. saxonica a typical univoltine cycle with summer and early autumn emergence was observed. Canonical correspondence analysis was used to define the relationship between environmental variables and larval stages. H. saxonica larval instars were distributed along temporal and nutrient gradients at all sampling sites, but differences were observed among sampling sites. The larval instars, prepupae and pupae of R. fasciata were distributed along water depth and oxygen concentration gradients, but temporal and temperature gradients were less important. [ABSTRACT FROM PUBLISHER]