Giant Flying Fox

The Giant Flying Fox is a Hardmode enemy that spawns only in the Jungle at night, in addition to the common Jungle Bats and in place of the Derplings that spawn during the day. Giant Flying Foxes can deal significant damage to a player and without any knockback resistance, can push players down jungle caves. They prove a threat to early Hardmode characters. They will not spawn in the Underground Jungle.

Trivia
The Flying Fox is one of the largest bats in the world, found mainly in the tropical regions of Asia. Thus, it makes sense for it to be the largest in-game bat.