The eastern dobsonfly is one of our largest non-lepidopteran insects. Its larvae, known as hellgrammites, are the top invertebrate predators in rocky streams where they occur. Adult male dobsonflies are particularly spectacular because of their large sickle-shaped mandibles (jaws). This 4-page fact sheet was written by Donald W. Hall, and published by the UF Department of Entomology and Nematology, April 2013.
http://edis.ifas.ufl.edu/in987