Whenever I saw butterfly, I thought 3dc-2dml/r-2mc-2aml/r-1st. Since that looks like a butterfly. But 3w-2dmc-2mc-2aml/r-1st kinda looks like a butterfly too.
I've been using these two formations a lot this year with great success (10 games, 50 goals, 2 conceded).
I use the 3dc version against any 3 St formation.