Fearsome and cunning, the great spiders of Middle-earth are descendants of Ungoliant, a spider queen of the First Age, and a source of the deepest and most sinister of shadows. Allied with Melkor she sought to plunge the world into darkness by consuming the light. In her greed she turned against her accomplice before having sufficient power to thwart him. Wounded in this endeavor, Ungoliant fled back into the dark mountain valley she had previously settled. Assured of retaliation, she bred offspring to strengthen her position, which spread to other places in the world.
Ungoliant passes from history at this point, but her offspring remain in many shapes, forms and degrees of intelligence, evil intent, and malicious personality. They continue the tradition that their matron established: temporary allegiance, self-centered greed, and always a great hunger - and fear - of light and life.
Whether acting as servants of Sauron or operating on their own evil intent, these giant spiders have a long history of animosity toward the Free Peoples. Always attempting to establish nests in secluded places and expand into settled areas where they can prey upon others. Luckily, few such permanent nests have been established, with the best known location being within the Forest of Mirkwood as Bilbo Baggins can attest.