- "There age-long she had dwelt, an evil thing in spider-form, even such as once of old had lived in the Land of the Elves in the West that is now under the Sea, such as Beren fought in the Mountains of Terror in Doriath, and so came to Lúthien upon the green sward amid the hemlocks in the moonlight long ago. How Shelob came there, flying from ruin, no tale tells, for out of the Dark Years few tales have come. But still she was there, who was there before Sauron, and before the first stone of Barad-dûr; and she served none but herself, drinking the blood of Elves and Men, bloated and grown fat with endless brooding on her feasts, weaving webs of shadows; for all living things were her food, and her vomit darkness. Far and wide her lesser broods, bastards of the miserable mates, her own offspring, that she slew, spread from glen to glen, from the Ephel Dúath to the eastern hills, to Dol Guldur and the fastnesses of Mirkwood. But none could rival her, Shelob the Great, last child of Ungoliant to trouble the unhappy world."
- ― The Lord of the Rings, Shelob's Lair
Shelob in the books
Shelob was a huge creature in spider form, high in the mountains of Mordor, the last of the spawn of Ungoliant. Shelob spent her early days feeding off elves and men. Later on when elves and men no longer traveled to Mordor on regular occasions, she was fed Orcs by Sauron. Sauron would often feed her captured prisoners that he had no further use for. Even though they could not communicate, they both understood each other. Shelob was like a pet to Sauron, and it was good because she guarded the pass of Cirith Ungol to prevent any intruders from entering the dark land.(She may have been a form of evil spirit, possibly a Maia or with Maiar blood, instead of an actual spider). Her lair was along the path that Sam Gamgee and Frodo Baggins took while seeking Mount Doom. Apparently she has some sort of understanding with Gollum, whom the Orcs of the Tower of Cirith Ungol call "Her Shelob's Sneak".
She attacked and stung Frodo, who lapsed into a death-like coma. Sam managed to defeat her by letting her impale herself upon Frodo's sword while trying to crush him, and she fled to her lair, wounded.
Thinking Frodo dead, Sam took the One Ring from him and left his body behind, but discovered by listening to a party of Orcs that Shelob's venom was not intended to kill its victims but only to render them unconscious and keep their meat fresh.
The name Shelob is derived from "lob", an archaic English word for spider. A variation, "cob" is the derivation of the word "cobweb". It is doubtless an Anglicization of the original Westron/Sindarin word, according to the Translator conceit.
In the movie, Shelob can be seen to have a retractable venomous sting at the rear end between the spinnerets, resembling a wasp's sting. This is very much unlike real spiders which inject venom with their fangs but accurate relative to the novel. Shelob also appears to have a gaping mouth, whereas real spiders can ingest only liquid. In the book, on the other hand, "clusters" of eyes are mentioned, which may suggest compound eyes like those of insects; the Shelob in the movie does not have compound eyes, which is appropriate. A hunting spider of the family Lycosidae, which Shelob most closely resembles, would have two large eyes facing forward, and a few smaller ones almost hidden below. The only spiders that can reasonably be said to have "clustered" eyes (though not true compound eyes) are the daddy long-legs spiders of the family Pholcidae, but Shelob does not resemble these rather spindly and fragile spiders in other aspects of her physique.