Stumbled across a cave one winter in Hainan, China, and heard the sound of a waterfall, so I ventured inside - but realized there was no water flowing out and the floor was covered with a sticky substance that I recognized as guano. I looked up to see a thousand bats rustling as they roosted; hence, the sound. How carefully I backed out of that cave one can imagine. They were Asian parti-colored bats, a migratory, insectivorous species who winter in southern Asia and move north in the summer to feast on the so very delicious insects inhabiting Japan. One knows summer has arrived when they return. Saw a bunch of them flitting about my neighborhood this evening. They are your friends: they can eat their bodyweight in mosquitos each evening. They often roost under rain gutters. Treat them well. - William https://en.wikipedia.org/wiki/Asian_particolored_bat