The Collaborative International Dictionary of English v.0.48:

Stagworm \Stag"worm`\ (st[a^]g"w[^u]rm`), n. (Zool.)
   The larva of any species of botfly which is parasitic upon
   the stag, such as Oestrus actaeon, or Hypoderma actaeon,
   which burrows beneath the skin, and Cephalomyia auribarbis,
   which lives in the nostrils.
   [1913 Webster]