The Collaborative International Dictionary
Corydalus \Corydalus\ prop. n. The type genus of the Corydalidae. It includes the dobsonfly ( Corydalus cornutus), whose aquatic larva, the hellgrammite, is used as bait in fishing.
Syn: genus Corydalus, genus Corydalis.
Hellgamite \Hell"ga*mite\, Hellgramite \Hell"gra*mite\, n. (Zo["o]l.) The aquatic larva of a large American winged insect ( Corydalus cornutus), much used a fish bait by anglers; the dobson. It belongs to the Neuroptera.
Dobson \Dob"son\, n. (Zo["o]l.) The aquatic larva of a large neuropterous insect ( Corydalus cornutus), used as bait in angling. See Hellgamite.
Wikipedia
The eastern dobsonfly, Corydalus cornutus, is a large insect in the Corydalidae family. It is found in eastern North America in regions with fast-flowing streams where its aquatic larvae develop. These are known as hellgrammites and are among the top invertebrate predators in the streams in which they live. They are used by anglers as bait.