Sadly, it isn't true that the word "butterfly" came from a metathesis (the changing around of the order of syllables) of flutterby, but it is still a nice idea.
The old English word was "buttorfleoge" - combining butter and fly, but there seems to be no agreement on why there is a butter reference. Some say that butterflies will go to butter if it is left out and uncovered....but I've never heard of that! Any ideas?
Maybe because they are attracted to butter colored flowers?.....but then they seem to like all different colored flowers... One of life's mysteries I guess.
But it doesn't take away from the enjoyment of seeing butterflies flutter by.