Stone Flies

insects of the order Plecoptera. Their wings are transparent, are folded flat on the back when at rest, and have a spread of from 10 to 80 mm. At the end of the body there are two long cerci. There are about 700 species, which live near flowing bodies of water. Stone flies are particularly diverse and numerous in mountainous regions. The widely distributed species Isogenus nubecula is characteristic of the large lowland rivers of Europe. The larvae, which have two cerci, are carnivorous and live on the bottom, staying among stones. The larvae prefer clean, oxygen-rich, cold water. Metamorphosis is incomplete. Their development is slow, continuing in certain species (for instance, Perla abdominalis) for more than three years. The exit of grown nymphs from the water and the emergence of grown insects begins in early spring. Stone fly larvae serve as food for commercial fish.