Butterfly's name

[sherrycp]

Why is it named a butterfly?

[Clanad]

Apparently the German word for butterfly is "milchdieb," which translates as "milk thief." Evidently there was a theory in the Middle Ages that the little critters steal milk and butter, a myth possibly based on their light, colorful wings and delicate appearance. Or perhaps they really did steal milk and butter. It's not impossible. Another possibility for the name is  that it comes from flutterby. An aliteration of the flight movements of the insect, What we do know, is that this word is very old (pre-8th century). It was originally buturfliog�, a compound of butere `butter' and fleoge `fly.' Why butter? Some suggest that it was due to many butterflies being yellow in color, like butter.

[Tim Baxter]

The reverend Spooner saw one flutter by!

[Quizmonster]

It's a lovely story that claims the word �butterfly' comes from the fact that one may be seen to �flutter by'. ..ie that it is just a letter-swop. Sadly that's all it is...a story. 
Even in Old English days, the words �butter' and �fly' were joined to create �butorfleoge' as the creature's name.  There may be a connection with a Dutch dialect word for butterfly...�boterschijte', which suggests a relationship between butter and butterfly excrement, both being yellow.  Unfortunately - though probably more accurate - that's not quite such a pretty picture as flutter-by!
Another theory is that �butor' was also the Old English name for the finest of pasture-land.  Obviously, many butterflies would be attracted to such grass and the cattle on it would produce the finest of butter...hence the name of the dairy product.
A strange thing is the fact that the word �butterfly' itself seems to come from different roots in each of the other four major European languages...French = papillon, Italian = farfalla, Spanish = mariposa and German = Schmetterling.