Bat

Bats are passive mobs that spawn naturally in caverns or other large enclosed spaces. Bats are the only passive mob able to fly, and the only flying mob that spawns in the Overworld. 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. Bats will spawn in pre-explored caves from older saves.

Trivia

 * Bats can spawn in a house if there is a large enough area for the game to think of it as a cave.
 * When placed in a minecart, bats can move the minecart around on their own.
 * Athough bats are currently peaceful mobs, the snapshot states they will be neutral mobs.
 * Bats cannot hang on transparent blocks.
 * Some people have encountered odd collision bugs with bats and blocks, specifically, they might be able to move up through diagonal roof of glass.
 * Bats are visually the smallest mob in the game.
 * Bats have no reaction to seeing wheat, and do not react to being Right-clicked with it either.

Gallery
Fledermaus Chauve-souris Nietoperz Летучая мышь 蝙蝠