Ladybird

I always presumed, as many have before me, that the word "butterfly" is a spoonerism of the word "flutterby," a description of its motion (maybe it was just something I came up with on my own, influenced by the Yiddish flaterl, meaning "little flutterer"). Boy, was I dead wrong. The Old English buttorfleoge is most probably a reference to the myth that witches disguised as butterflies would consume uncovered milk and butter. They didn't think that they were just butterflies or whatnot. Had to be witches, eh? The German schmetterling lends support to this theory seeing as it means "cream thief." (Compare schmetter with smetene, the Yiddish for sour cream, and tseshmetern, to smash, also Yiddish.) The Russian babochka helps out too - it means "grandmother," something akin to a witch.
Anyhow, an alternate suggestion is the fact that its waste resembles butter, supported by the Dutch boterschijte (do you recognize any cognate there? I'm not sure I see the connection between excrement and schijte - do you?).