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And NOT be sexy? My god, woman. I’m …

And NOT be sexy? My god, woman. I’m a plastic surgeon, not a miracle worker!

Butterfly answer, plus a little controversy
I’m inclined toward the association with butter and the name “botervlieg” in Dutch; butter churning was done in spring when butterflies came out, and I think it’s possible that butterflies would be attracted to the salt (and maybe trace minerals) which was added to butter, which they need for reproduction. Butterflies will also extract sodium and other minerals from dung, which is readily available in the pastures of dairy farms.

My feeling is that “butterfly” is one of those common names which comes from obvious, unique behaviors, and “butter-like excrement” is not very obvious because of the short time which butterflies will excrete anything, and that their excrement does not usually have the appearance of butter.