Also, Black Widows at least are near impossible to kill aside from running up and smooshing them.
If you use bug bombs or bug spray, they slow their damned metabolisms and close up their breathing holes (ventricles is the corect term I believe) until the poison has dissisipated, then walk off. Course they curl up like they're dead while they're doing this, so you don't know they lived until you come back to where you sprayed down eight or so of them an hour ago and not a one is there still.