J.R.R. Tolkien calls the giant spiders’ forest in The Hobbit Mirkwood.
Mirkwood is the great forest of northern Middle-earth that Bilbo and the Dwarves must cross on their journey to the Lonely Mountain. Its darker southern region is associated with the stronghold of the Necromancer, later identified as Sauron. The forest is dangerous because travelers can become lost, supplies run low, and giant spiders attack the company.
Bilbo’s encounter with the spiders is a major turning point. He rescues the Dwarves and names his sword Sting after using it against the creatures. The Wood-elves then capture the company, leading to the barrel escape toward Lake-town.
Mirkwood was once called Greenwood the Great. Its name changed as the influence of the Necromancer spread, and after Sauron’s defeat it became known as Eryn Lasgalen, the Wood of Greenleaves. It is distinct from Fangorn Forest, which lies farther west and is inhabited by Ents.