The Great Grass Harp is one of the treasures of the Great Ga'Hoole Tree. It was known for its beautiful music when the grass strings are strung through. It was brought to the tree by the renowned singer Cornelia Plonk. No one knew who invented it.
The harp can be played only by the nest-maid snakes. The first harp player was Cornelia's nest-maid snake. A guild was made for the other nest-maids to learn how to play it in strumming through different sections of the strings, making harmony together.
One notable Harp Guild member is Mrs. Plithiver, Soren and Eglantine's nest-maid snake. She was a sliptween, a snake that was specially tasked with jumping between octaves, striking each of the eight tones of the scale.