Any member of the Order Plecoptera. There are over 1,900 recognized species world wide, with 595 found in North America. Many are scrappers (i.e., algae eaters), while others prefer to eat insects (i.e., entomophagus). They are among the oldest examples of aquatic insects, and the first ones to emerge onto the land were without wings. Stone flies undergo incomplete metamorphosis (see: Developmental Cycle) and can take several years to mature in the stream before hatching.