The short answer is — most likely not.
Why is a butterfly called a butterfly? According to the Oxford English Dictionary, the reason is unknown! However, two possible derivations are offered: (1) from the Anglo-Saxon butterfleoge (literally butterfly) so called after the yellow species, and/or from the Old Dutch boterschijte from the colour of the excretion of Cabbage White! (2) Another is that butterflies were on the wing in meadows during the spring and summer butter season while the grass was growing.
There is also 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.
Literary references to ‘flutterby’ are quite few and the etymology shows that ‘butterfly’ is quite ancient. As to the origin of ‘flutterby,’ there are examples of the transposition of syllables in the usage of children, such as basketti for spaghetti, pillercat for caterpillar, and flutterby for butterfly. An 1867 book by American journalist, Marcus M. (Brick) Pomeroy, called Nonsense, contains these lines:
Beautiful as a flutterby,
And none could compare
With my pretty little charmer
And her rich, wavy hair.
So, there you have it. It is unlikely that the original word for butterfly was flutterby. I’ll leave you with a quote:
“Literature and butterflies are the two sweetest passions known to man.” — Vladimir Nabokov