The bat attaches itself onto a regular or blocker or special bubble, except the bubbles covered by Clouds or Spider Web environment, and does not let go until you match it. If you drop it, not like Bat Bubble in Bubble Witch 2 Saga, in which the Bat is fixed with a bubble and flied back onto the board, in Bubble Witch 3 Saga, only the Shoo Bat is flied back onto the board and will attach onto any bubble with the exception above.
These annoying little rodents attach themselves to bubbles. The only way to destroy a bat is to create a match with the bubble they have made their home. If their bubble falls (rather than being destroyed) they will flap their annoying little wings and find somewhere else to rest.