Bats are passive mobs that spawn naturally in the Overworld, but underground. They have the ability to fly, like Ghasts.
Bats spawn naturally in the overworld in caves underground. When spawned using its Spawn Egg on a block, it automatically hangs upside down.
During sunlight, bats will go to a block and sleep on it. Once the player approaches them, they will wake up and fly away. They cannot hold up in non-solid blocks.