Bat

Bats are passive mobs that spawn naturally in caverns or other large enclosed spaces. They sleep during the day and become active at night. A bat will hang upside down when it is idle, but once the player approaches, the bat will fly away. Bats tend to fly incoherently and sometimes run into lava. Bats are hard to see when in an unlit environment. They may have been created to nerf or ruin many mob spawners.

Trivia

 * Bats can spawn in a house if there is a large enough area for the game to think of it as a cave.
 * Bats are the only passive mob able to fly, and the only flying mob that spawns in the overworld.

Gallery
Fledermaus Chauve-souris Nietoperz Летучая мышь 蝙蝠