We studied aspects of the nymphal biology and ecology of 3 Perlodidae species (Guadalgenus franzi, Hemimelaena flaviventris, and Isoperla curtata) in a Mediterranean seasonal stream in the southern Iberian Peninsula. Their life-history strategies were greatly influenced by the characteristics of their environment, i.e., a summer dry period with relatively warm temperatures, but strategies differed among species. Guadalgenus franzi was semivoltine and probably underwent nymphal quiescence when the stream was dry. Hemimelaena flaviventris and I. curtata had relatively short univoltine life cycles that overlapped, but I. curtata was slightly ahead of H. flaviventris. Both species passed the dry period in the egg stage, probably with a diapause phase. Growth rates of H. flaviventris and I. curtata peaked before emergence, whereas growth rate of G. franzi peaked immediately before and after the dry period. The 3 species had relatively short flight periods compared with other species from seasonal streams. Guadalgenus franzi and I. curtata were mainly scrapers that fed on diatoms, whereas H. flaviventris was mainly predatory. Diet changed somewhat in relation to size, and prey electivity patterns differed among species. All 3 species preferred Chironomidae, but G. franzi preferred Chironomidae principally when smaller. All 3 species had high secondary production relative to other stonefly species from both temporary and permanent waters.