Butterflies have four wings. Can they fly with only two?
This question arose this week. My wife and daughter had picked up a butterfly cocoon to see how the butterfly emerged and later free her. But our naughty/lovely cat bit on the cocoon. So when the butterfly came out, her right wings were damaged. She couldn't fly.
Still, to answer the question of this post, if the hind wings are missing, butterflies can fly, their flight is amazingly robust. This is a nice example of how reductionism fails to see the function of systems by ignoring their interactions. You can have two out of four wings, but a butterfly will fly or not, live or die, depending on how the remaining wings interact. Looking only at individual wings will not tell you much about the capabilities of the insect.