Since you did the punkin lines around the sides of your last set, perhaps you could do webbing around the sides on these caps? Unfortunately, it's difficult to make a spider as... expressive as a jack-o-lantern.
The spider could be cartoony for more expression potential, or... i dunno! different sizes/designs of spiders on webs?
note: i'm at work, making due with the barest of graphic design tools here (microsoft word). I am not proud of what I've done here today. D: