What was Shelob, and more importantly, what was Ungoliant?

[Zigûr]

Originally Posted by mhagain

On the other hand if she was a spirit created within Ea but outside of Arda, subsequently corrupted by Melkor, it matches with everything in the texts and creates fewer contradictions and doubts.

I think this is an interesting idea. In Morgoth's Ring, essay II of "Myth's Transformed" mentions that "The Stars, therefore, in general will be other and remoter parts of the Great Tale of Eä, which do not concern the Valar of Arda. Though, even if not explicitly, it will be an underlying assumption that the Kingdom of Arda is of central importance, selected amid all the immeasurable vast of Eä as the scene of the main drama of the conflict" and shortly after Varda is described as "one of the great Valar of Arda."
This seems to corroborate with the idea which I believe Professor Tolkien speculated upon elsewhere (although I cannot find it immediately), that other Ainur may have been at work in other, notionally less important, regions of the cosmos. I think that might add to the notion that Ungoliant could quite literally be an "alien" creature, a being deriving from within Eä but not from the Solar System of Arda.