The Great Spiders of Middle-earth appear to have originated from Ungoliant. In the First Age, they lived in the Mountains of Terror in Beleriand, drinking the blood of all who came near. They served nothing but their never-ending hunger.

In the Third Age, most Giant Spiders lived in Mirkwood. They attacked Bilbo and the dwarves when they tried to cross Mirkwood in the Quest of Erebor.

The last of the known Giant Spiders was Shelob.
Encyclopedia entry originally written by Haldish