De Vermis Mysteriis, or Mysteries of the Worm, is a fictional grimoire created by Robert Bloch and incorporated by H. P. Lovecraft into the lore of the Cthulhu Mythos.
The tome first appeared in Bloch’s short story ”The Shambler from the Stars” (1935), in which a character reads a passage from the book and accidentally summons an extradimensional horror.
Bloch, then a teenager, corresponded with Lovecraft about the story prior to its publication, in part to get permission to kill off a character based on the older writer. While giving his enthusiastic blessing, Lovecraft also suggested that the book featured in the story, named by Bloch as Mysteries of the Worm, be referred to instead by the Latin equivalentDe Vermis Mysteriis.
Lovecraft also provided Bloch with a bit of Latin to use as an invocation from the book: “Tibi, magnum Innominandum, signa stellarum nigrarum et bufoniformis Sadoquae sigillum”—which can be translated as “To you, the great Not-to-Be-Named, signs of the black stars, and the seal of the toad-shaped Tsathoggua”.
Lovecraft, who enjoyed sprinkling references to his friends’ fictional creations in his own Cthulhu Mythos efforts, repeatedly mentioned De Vermis Mysteriis in his stories. It appears in “The Haunter of the Dark" (written as a sequel to Bloch’s "The Shambler from the Stars") as a "hellish" book found with other forbidden texts in the Starry Wisdom Church inProvidence, Rhode Island. In “The Diary of Alonzo Typer”, ghostwritten by Lovecraft for William Lumley, it is likewise part of an occult library in the van der Heyl house in Attica, New York. And in Lovecraft’s “The Shadow Out of Time”, the possessed protagonist Wingate Peaslee reads (and makes marginal notes in) a copy of the book possessed by theMiskatonic University library.
In a 1936 letter to fellow Mythos writer Henry Kuttner, Lovecraft mentioned De Vermis Mysteriis as one of the books that “repeat the most hellish secrets learnt by early man”.
The book is referenced (as Des Vermis Mysteriis) in the 2004movieHellboy. It contains a description of the Ogdru Jahad, gods otherwise not connected to the Cthulhu mythos.