I have never been bitten by a spider so I can't answer about their bites. One thing that I think you need understand about snake bites is that there are different types of bites. The usual bite is due to a snake's nervousness and this type of bite rarely hurts at all because the snake tags you and lets go immediately. The other type of bite is when the keeper makes a mistake and is bitten during feeding time. A feeding response bite from a python or boa can involve constriction and the snake generally does not want to let go and the more you move the harder the snake bites and constricts. I have made my share of dumb moves over 35 years of keeping snakes and I can tell you that even a 6' carpet python can deliver a bite that hurts when it thinks that your hand is food.