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The members of the Perlidae family are big insects. In the larval stadium they are carnivore and prey on smaller larvae. They hatch by climbing on emerging rocks or vegetation to exit the exuvia as winged insect once that are out of the water. The nymphs are preyed by the trout when snatched by the current or while crawling on the submerged bottom. (Photo: Perla marginata in a freestone cold river in June, 200 m. ASL.)