Thereās something so ominous about the repeated notes throughout Tolkienās histories that Ungoliant took the form of a spider, the obvious implication being that she isnāt one, sheās something else, something worse.
In Morgothās Ring it says she takes the form of a spider so she can weave āwebs of strangling gloomā to catch light.
We actually get similar language with Glaurung who is repeatedly described as a spirit in the form of a great, wingless dragon. But though this does raise fascinating questions about Glaurungās nature and the precise mechanisms through which he was created, we do at least know he was created in Angband by Morgoth
With Ungoliant, there is so such detail. Her first mention in The Silmarillion speaks of her through heresay, what is believed of her without offering a definitive answer. It was said that she ādescended from the darkness that lies about Ardaā and while Melkor sought her service early, her lack of allegiance to him began long before the darkening. Indeed there are similarities in the way Ungoliantās āunlightā and the Shadow Morgoth casts are described
Ungoliantās horror comes primarily from her relationship to light and her hunger. The Unlight she creates is not just darkness, it is thick with a paralysing, venomous despair
Itās worth noting that this phrasing, that the Eldar knew not where she came from, is repeated in every draft of the darkening as well as the official Silmarillion. And of course this unknowing only adds to the horror she inspires
Anyways just something Iām thinking about; I really love entities like Ungoliant and the Watcher in the Water, and what their existence means about the larger legendarium