The Collaborative International Dictionary of English v.0.48:

Grugru worm \Gru"gru worm"\ (Zool.)
   The larva or grub of a large South American beetle (Calandra
   palmarum), which lives in the pith of palm trees and sugar
   cane. It is eaten by the natives, and esteemed a delicacy.
   [1913 Webster]