Symbolism, Imagery, Allegory
Raskolnikov is associated with blunt and sharp instruments, blood, nightmares, and to some degree horses (see his horse dream). These might make our skin crawl, but they aren't real creepy-crawly symbols. Unlike Svidrigaïlov, he doesn't have any spider or rat issues.
Speaking of Svidrigaïlov, what did you think of his idea of the afterlife?
We always imagine eternity as something beyond our conception, something vast, vast! But why must it be vast? Instead of all that, what if it's one little room, like a bath house in the country, black and grimy and spiders in every corner, and that's all eternity is? I sometimes fancy it like that. (4.1.84)
This even gives old Raskolnikov "a cold chill."
Svidrigaïlov doesn't think this is a bad thing. He puts this forth as his ideal. Perhaps he's bluffing to freak out Raskolnikov, or perhaps he really believes something like that is in store for him. Would he kill himself if he knew he was going there? How does that compare with some other ideas of the afterlife, or hell (since many people would say that's where Svidrigaïlov is going)?
Doesn't the hideous hotel room he stays in his last night seem a little like his idea of the afterlife? It's tiny and dark. Only, instead of spiders, he gets….mice and rats crawling on him and trying to eat his cold (disgusting) veal. Throw in some nightmares and the room with the spiders isn't looking so bad anymore, even to us.