"Flutterby" is a better name for them, isn't it? But no; English has always called them butterflies (buterflie, in Middle English, and buttorfleoge, in old English).
It's not clear where that name comes from. Some dictionaries speculate that the word comes from the old Dutch word boterschijte, meaning droppings that look like butter -- but butterflies excrete only water, and caterpillar frass looks nothing like butter.
Our word for butterfly is kind of boring, compared to other languages'. In ancient Greek and ancient Latin, the words for butterfly -- psyche and papilio -- were also used to describe the human soul. Our word pavilion comes from the Latin word for butterfly -- the underlying image is of something that spreads out. This website explores different languages' words for butterflies, and their origins.
Wishing Anna Bragdon a very happy birthday today, which is otherwise kind of grim. Another winter storm is coming; soldiers are not coming home from Iraq and Afghanistan; and Kurt Vonnegut is dead. Damn it.
It seems appropriate to close on this quotation, which was in the Times' obituary. It's from God Bless You, Mr. Rosewater, published the year I was born:
"At the outside, babies, you’ve got about a hundred years here. There’s only one rule that I know of, babies — ‘God damn it, you’ve got to be kind.’ ”