The spider rat was a Safeholdian native species which filled roughly the ecological niche of terrestrial rats.
Like all Safeholdian mammals, it was hexapedal (six-limbed), but it looked like a cross between a hairy gila monster and an insect, with long, multi-jointed legs which actually arched higher than its spine.
These creatures were known to be nasty tempered, but basically cowardly, and fully adult male specimens of the larger varieties of spider rat ran to about two feet in body length with another two feet of tail. The more common varieties averaged between a third and half of that body/tail length. (OAR)