Atlach-Nacha (The Spider God) superficially resembles a giant hairy spider with a hideous, vaguely human face. He came from Saturn with Tsathoggua. He dwells underground (in Mount Voormithadreth) and spends his æons spinning a weird web. One legend claims that he was imprisoned beneath a mountain in Siberia (but this might be one of the sundered peaks of Voormithadreth). It kills its victims by puncturing them with thousands of spins and sucking out their juices. He is subservient to Abhoth and is served by the “Grey Weavers” (who might be the Spiders of Leng). A burial ritual in the Book of Eibon references this god.
It had a cult among the Phoenicians and the Hyborians (where he was known as Zath). In modern times Atlach-Nacha is worshipped the Tcho-Tcho of the Andaman Islands and South Asia. Atlach-Nacha was created by Clark Ashton Smith; it has been mentioned or elaborated upon by August Derleth, Colin Wilson, Brian Lumley, Lin Carter, Laurence J. Cornford and by some Chaosium products.