What is the etymology of butterfly?

Some claim that the butterfly had originally been named as flutterby or even that Shakespeare was responsible for changing the name. The truth is that the word butterfly really means butter-fly: a fly (or flying animal) that was supposed to like butter or whose excrements resemble butter. The link with dairy products is not only evident in English: the German name "Schmetterling" is derived from "Schmetten", the word for "cream" in some German dialects.