How high can spiders jump, and can they leap up on to a wall and climb from there? For instance, can a spider jump up to the lip in any of these (O is ground, X is wall):
X
X XX
X XX X
XX X X
X X X
OOOOOOOOOOOOOOOOOO
Everyone says you need to put a lip on your wall to keep spiders out, but nobody says if there is a minimum height before it is effective.