For what is this fur? Answer is easy – butterflies needs to have a certain temperature to fly – so muscles could provide the required number of strokes of the wings. If butterfly is in the sun – it’s very easy, is only to substitute the body warm by rays. But if the butterfly is in shadow or, in general, is nocturnal, then it will have problems with warming. Therefore, it is a coat and to keep body warm and not to depend on the ambient temperature.
Long hairs around wings help to lessen air resistance and control the fly.
Also, furry coat helps butterflies to escape from their enemies – bats. After the mouse while hunting for guided ultrasonic waves – inaudible squeak tonyusenkoy us. Bouncing off the walls and other objects, the ultrasonic waves are returned back, passing the bats ears and bat can see everything like on the radar screen. But if the surface on which the sound waves falls is hairy, it will not reflect it back accurately, and scattering in different directions. And bat is confused where exactly it flys, and whom exactly it missed.