I used the bigger round magnets (which were stronger) for the big spiders and the roll of magnet tape that you cut to size for the smaller spiders.
Completely creepy and something the kids can help you with. Bug thinks these are especially cool and loves putting them in different positions. I'm not a fan of spiders, but I'll put aside my fears for these fun guys!
(on a totally unrelated note, do you know how hard it is to type when holding a baby??)