Spiders?

[Celebuial]

I have noticed that giant spiders that aren't really spiders at all, but just physical manifestations of something which descended from the Darkness outside of the Universe, seem to keep cropping up everywhere...

Well not being a very well read person I started to wonder that seeing as Tolkien has an ongoing theme with evil spiders (Ungoliant, Shelob and even the spiders of Mirkwood) and other authors such as Stephen King (in IT the spider practically is Ungoliant) & Rowling have the same idea, that unless they simply copied Tolkien there must be some kind of myth or something where evil 'spirits' from 'outside' present themselves in the form of spiders.

I guess that most of you guys have read the letters and HoME (I'm only on the 3rd volume!!!), so you can probably fill me in on where the spider thing comes from... If not I'm sure lots of you learned 'Downers are interested in Mythology and stuff...