If this is a question of first impression, I'd vote for "flutter".
However, it must be admitted that a poster framed on my wall, collecting such terms, says "a rabble of butterflies". (Googling this term produced many lists that include it, but I've found none that cites a primary authority.)

note to paulb: I too checked Lipton's book, without success. However, Lipton cites The Book of St. Albans, 1486, as the seminal authority. Any idea how to find that, or any reprint, to check for butterflies? My weak googling skills aren't up to the task.