The Collaborative International Dictionary of English v.0.48:

Gribble \Grib"ble\, n. [Cf. Prov. E. grib to bite.] (Zool.)
   A small marine isopod crustacean (Limnoria lignorum or
   Limnoria terebrans), which burrows into and rapidly
   destroys submerged timber, such as the piles of wharves, both
   in Europe and America.
   [1913 Webster]