The Big spider is the giant spider of Llewdor. They are a species of giant spider native to Llewdor. The females are blue colored, and have red eyes. Alexander dropped her into the sea while in the form of an eagle. They are apparently non-sentient.
Big red spiders can be found in Eldritch, and capable of communicating with humans as well. Though these are a bit smaller than the giant spiders, but still larger than the garden variety spider.