The Collaborative International Dictionary of English v.0.48:

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.
        [WordNet 1.5 +PJC]

The Collaborative International Dictionary of English v.0.48:

Dobson \Dob"son\, n. (Zool.)
   The aquatic larva of a large neuropterous insect (Corydalus
   cornutus), used as bait in angling. See Hellgamite.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Hellgamite \Hell"ga*mite\, Hellgramite \Hell"gra*mite\, n.
   (Zool.)
   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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Corydalus cornutus
    n 1: large soft-bodied insect having long slender mandibles in
         the male; aquatic larvae often used as bait [syn: dobson,
         dobsonfly, dobson fly, Corydalus cornutus]