Butterfly flutter by

Today I watched a hoooge butterfly flutter past my bedroom window and wondered...why is it called a butterfly and not a flutterby? The second seems to make a lot more sense to me!

Here's the origin of the word, according to the Online Etymology Dictionary. Interesting!!

O.E. buttorfleoge, perhaps based on the old notion that the insects (or witches disguised as butterflies) consume butter or milk that is left uncovered. Or, less creatively, simply because the pale yellow color of many species' wings suggests the color of butter. Another theory connects it to the color of the insect's excrement, based on Du. cognate boterschijte. A fascinating overview of words for "butterfly" in various languages can be found here. The swimming stroke so called from 1936. Butterflies "light stomach spasms caused by anxiety" is from 1908.