Some bats eat flies, mosquitoes and other insects. They do not harm people. Only the South American Vampire bat attack cattle. Some bats eat fruits and help pollinate the fruit trees. At the same time, they do, however, damage the fruit.
Snakes eat mice, rats, and lizards.
Some snakes are poisonous, but not all. Even poisonous snakes bite humans only if threatened or surprised. Spiders eat mosquitoes, flies and ants. They do not harm people. Only some very large spiders may inflict a painful bite to humans.