The arangma in the dungeon can still be a bit aggressive. Sometimes I get through with no problems, but other times they attack without provocation. The one near Zak has given me several problems. I'm guessing that if you get within some distance, it triggers a response, but in the dungeons, there isn't really any room to go around. I don't mind the webs, but when they web you, attack you, and poison you, it's no fun.
I've had similar problems in the sewers, but usually there's enough room to go around them.