Useless bats

Sort of a late add on to the caves update. Bats are useless and only for ambience. But, in real life there are caves meant for bats. So, why not make a cave biome addition for bats. The biome would spawn occasionally and be more rare than lush caves, but maybe as frequent as azalea surface trees. They swarm around in the night, may or may not need to add mosquito creature for them to eat, or a certain fruit tree, or if they suck blood causing damage. (Depends on the bat type you add) They enter their cave slot entrance by night and sleep in mass on the ceiling. (in this biome there will be a lot of entities, which may cause lagg.) Their guano(poo) is a super fertilizer and restored dead dirt. Maybe in game, their one block guano layer at bottom of cave, regenerates after so many days. Their guano can create bonemeal, and maybe turn course dirt into grass or regular dirt. Maybe when these cave bats are killed, they drop wing membrane. Which after you collect and craft 9 together, they make a standard membrane like the phantoms drop, to repair elytra. And, in comment I just read, their wings could be used for brewing.