Ungoliant would be a dreadful encounter indeed:
Greatest of the giant beings that took Spider form was she, a mighty and evil spirit that entered the world before the Trees of the Valar were made. She was dreadful and vile and possessed of a web of darkness called the Unlight of Ungoliant, which not even the eyes of Manwe could penetrate. She came with Melkor to Valinor and destoyed the trees of the Valar. She even tried Melkor as her prey, who called the demons of fire named Balrogs to come and lash her with their whips of flame. Breeding with other great spiders, her gluttony was a fearful thing and it is said in her ravening hunger that she finally consumed herself in the deserts of the South...Perhaps, not!