Also as for your spider conundrum, there are two things you can do to avoid them pranking you. One is a scapegoat, enlist a student that gains your full trust to act like they have a fear of spiders, or maybe one that has a fear of real spiders but not fake ones, and then you'll have to recruit a spider assassin on that student's benefit. You'll have your spider assassin(s) but no one will know it's actually you that needs it, so they'll never prank you.
Until of course you see a spider next to you and run out the door and leave your class behind. They may figure it out then.
Which leads to the second option, when they find out that you're deathly afraid of spiders, threaten them with an F or something around the same severity. That's about the only way I can think of to stop the pranks.
--
~Halo Everybody run!
http://img9.imageshack.us/img9/6195/furriese.jpg