Yaddith is a distant planet that orbits five suns. Aeons ago it was inhabited by the Nug-Soth, creatures with traits similar to mammals, reptiles, and insects. The Nug-Soth sought a way to prevent the destruction of their planet's crust by the Dholes, but to no avail. Eventually, the Dholes overwhelmed them and destroyed the Nug-Soth's civilization. Survivors of the catastrophe escaped, however, and hid on various planets. Life on Yaddith amongst the Nug-Soth and the Dholes that threatened them was first described in detail in Through the Gates of the Silver Key as Randolph Carter is stranded there for hundreds of years while sharing the body of Zkauba the wizard, though Lovecraft did not name the race that inhabited the planet.
Robert M. Price's short story Saucers from Yaddith (1984) hints that Nug-Soth scientists have appeared on Earth performing various experiments on humans—some relatively harmless (such as changing a man's blood type from B to A), some rather bizarre (two brothers in medieval Germany claimed that an "angel" had switched their hands and eyes), and others utterly horrific or disgusting.