Bat

Bats are flying passive mobs that spawn in caves.

Spawning
Bats can spawn anywhere in the Overworld at a light level of 4 or less on opaque blocks below layer 63.

Behavior
Bats 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 cannot hang on transparent or non-solid blocks.

They are the 4th smallest mobs in the game.

Bats will squeak (similar to its real life function of echolocation).

Although the bat is a passive mob, they still despawn when going too far away, like hostile mobs, ocelots and squid.

Bats do not recognize lava as obstruction and can fly into it.

Bats will see players even when they are invisible.

Trivia

 * Bats tend to fly to the east whenever given a choice.
 * It is impossible to attach a lead to a bat.

Gallery
Fledermaus Chauve-souris Murciélago Pipistrello Vleermuis Nietoperz Летучая мышь 蝙蝠