I dunno why.  Always have.  Maybe it's their...buggish appearance or maybe it's the way they move.  Everytime I play a game with spiders in it, I'm filled with dread if they look realistic, somewhat. 

Take Dungeon Siege for instance.  You have to go through a tower with an ENDLESS supply of spiders.  The gigantic one at the end wasn't so creepy since it didn't look too real, though.  I also hated that part in Warcraft III (I think it was Warcraft III....it may have been the expansion or both) where there were these big spiders.

Ocarina of Time freaked me out when I was younger, but since I've gotten older the Skulltullas don't scare me.  They don't look to real, which is why I can put up with the Skulltullas in Twilight Princess.

Resident Evil 4....well, a spider-like parasite has led me to postpone playing it for a while and start up playing Prince of Persia: The Two Thrones again.  I'm inside the castle part in RE4 and I blow up a monk's head.  A parasite comes out, unlike one I've ever seen.  It's wiggling.  I take out my gun and run, then shoot it from a distance.  The monk falls down but the parasite detaches from its head and comes after me.  I ran out of the room and took out my rifle and zoomed in on the open doorway.  When the parasite came through I blasted it.  Then it curled up and died.  Gross, I know.  I don't know what this parasite will do, or the other one that comes out of the monks' heads.  Guess I'll take a look at the guide.  I DO know what the first, less-creepy one does.  All it does it swing a sharp point at you, which isn't too freaky.

Again, I LOATHE spiders.