A spider built a small web on my Arduino (it's in my crawlspace). so it may have had to do with that?
Spider webs are non-conductive. The spider itself probably has some very-high resistance (I think you can electrocute a spider with enough voltage) but in a digital circuit it's not going to cause any trouble. Now.... if a mouse urinates on the board it might be damaged, but probably more by corrosion than by conductivity or "shorting-out".