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

[Inziladun]

Originally Posted by mhagain

As to what these spirits are, Tolkien doesn't say but I consider it doubtful that they're Ainur. The Ainur were created outside of (and before) Eä, whereas these seem to me to have been created within Eä and are part of it ("spirits out of the halls of Eä").

The spirits summoned by Manwë and Yavanna though seem to be lesser beings brought for service. Upon their arrival, they began to fulfill a specific purpose as ordered by the summoner. The same cannot be said for Ungoliant (or Tom Bombadil ).
That is why I see Ungoliant having a greater power with more independence of thought than the garden-variety Maia.