The objectives of this study were to describe the effect of drying out on the composition of the mayfly taxocene and evaluate the relevance of individual species traits for survival of mayflies to drying out.Their taxocenes of two localities,one at intermittent and one at permanent brook,were investigated in 2002,2003 and 2005.Compared with the permanent stream,the taxocene of the intermittent stream was short of nine species,foremost rheobionts and high oxygen demand species.To explain further differences between both stream in survival and recolonisation ability,15 species traits were evaluated.These ecological traits(e.g. habitat and substrate range,density distribution,current velocity adaptation)and biological traits connected with life cycle and larval-adult adaptations.Species showing highest number of advantageous traits(with only exception of Electrogena sp.cf.ujhelyii-species of taxonomically unclear status)were able to successfully survive under unfavourable conditions of intermittent brook.