The Silmarillion » Allies of Morgoth
Thuringwethil – “Woman of Secret Shadow”, she was a vampire messenger of Sauron from Tol-in-Gaurhoth who took the form of a she-bat. Her wings were barbed with an iron claw at each joint. She may have been a Maia spirit. Lúthien disguised herself as Thuringwethil when she entered Angband.
Ungoliant – “Dark Spider” in Sindarin or Wirilomë “Gloomweaver” in Quenya, she was an evil spirit (Maiar?) in the form of a giant she-spider. Along with Melkor, she destroyed the Trees of Valinor by draining the Trees of their sap. They then both fled to Lammoth, in northwest Beleriand. She lusted for the Silmarils that Melkor has stolen and fought with him. However, Melkor gave out a great cry and his Balrogs came to his aid causing Ungoliant to flee to Ered Gorgoroth, the Mountains of Terror. She dwelt there and had many monsterous offsprings which infested those mountains. She was also the mother of Shelob.