What is a hellgrammite?

hellgrammite larva

   The hellgrammite is the larva of a four-winged insect known as the donson fly. Hellgrammites live under stones in swift streams of North America. They have strong jaws and prey upon small water animals. Bass fishermen like to use them for bait because they wriggle about. When hellgrammites are fully grown they leave the water, pupate for about two weeks, and emerge as dobson flies.
   Scientific Classification. Dobson flies belong to the order Neuroptera. They are classified as genus Corydalus, species C. cornutus.