The Collaborative International Dictionary of English v.0.48:

Silkworm \Silk"worm`\, n. [AS. seolcwyrm.] (Zool.)
   The larva of any one of numerous species of bombycid moths,
   which spins a large amount of strong silk in constructing its
   cocoon before changing to a pupa.
   [1913 Webster]

   Note: The common species (Bombyx mori) feeds on the leaves
         of the white mulberry tree. It is native of China, but
         has long been introduced into other countries of Asia
         and Europe, and is reared on a large scale. In America
         it is reared only to small extent. The Ailanthus
         silkworm (Philosamia cynthia) is a much larger
         species, of considerable importance, which has been
         introduced into Europe and America from China. The most
         useful American species is the Polyphemus. See
         Polyphemus.
         [1913 Webster]

   Pernyi silkworm, the larva of the Pernyi moth. See Pernyi
      moth.

   Silkworm gut, a substance prepared from the contents of the
      silk glands of silkworms and used in making lines for
      angling. See Gut.

   Silkworm rot, a disease of silkworms; muscardine.
      [1913 Webster]