'…and fleeing from the north she went down into Beleriand, and dwelt beneath Ered Gorgoroth, in that dark valley that was after called Nan Dungortheb, the Valley of Dreadful Death, because of the horror that she bred there. For other foul creatures of spider form had dwelt there since the days of the delving of Angband, and she mated with them, and devoured them; and even after Ungoliant herself departed, and went whither she would into the forgotten south of the world, her offspring abode there and wove their hideous webs. Of the fate of Ungoliant no tale tells. Yet some have said that she ended long ago, when in her uttermost famine she devoured herself at last.'
- Of the Flight of the Noldor, The Silmarillion.
Ungoliant, Mother of all Spiders, by JJ Red