Hellgrammite, << HEHL gruh myt, >> is the wormlike larva (immature stage) of the four-winged insect known as the dobsonfly. Hellgrammites live under stones in swift streams of North America. They have strong jaws and prey on small aquatic organisms. They are a popular fishing bait because they wriggle about on the bait hook. When hellgrammites are fully grown, they leave the water, pupate for about two weeks, and emerge as dobsonflies.