The bats first appear in The Lost City and Sunset Vista, where they attack Crash in swarms. The only way to get rid of the swarms of bats is by spinning away the lone bats on each side of where the swarm enters and leaves, hanging from the wall, as they are the ones summoning them.
Crash is able to spin the swarm of bats away, though if he gets caught in their path he will lose an Aku Aku or a life. However, they can usually be avoided by waiting on lower ground until they fly by. The bats also appear in a swarm in certain areas of Temple Ruins and Jaws of Darkness, but are not commanded by a lone bat. Wumpa Fruit will come out of the bats in The Lost City and Sunset Vista when spun. In all levels containing bats, Crash should stay low when the bats fly over to avoid them.
Crash Bandicoot: The Wrath of Cortex
The bats reappear in Crash Bandicoot: The Wrath of Cortex in the Wizards and Lizards level. In this game, they appear as small purple bats that fly around in circles, causing danger if Crash tries to jump in the air. They can be easily defeated by spinning them away at anytime. If Crash is hit by the wizard's magical energy in this level, then he will turn into a bat similar to the ones in the same level.
It was originally planned that they would appear in the level Jungle Bungle, in which they were going to come out of the caves and spread across the level, and in the level Cavern Catastrophe where they would have attacked Crash and Cortex if they stayed still for too long.
Crash Bandicoot N. Sane Trilogy
Bats are scheduled to reappear in the Crash Bandicoot N. Sane Trilogy where they play the same role as they did in the original version of the game.
There is another unseen bat depicted in a green gem gallery in Crash Twinsanity, along with the white variant. This particular bat is purple and dark red in color and looks to be hanging upside down. It is currently unknown where it would have been encountered, however it likely would have appeared in the Cut Temple Level.