The mark of the butterfly (5)
I believe the answer is:
comma
I believe this clue is a double definition.
'the mark' is the first definition.
(comma is a kind of mark)
'the butterfly' is the second definition.
(comma is a kind of butterfly)
'of' is the link.
(Other definitions for comma that I've seen before include "List-item separator" , "Puncuation mark" , "Punctuation mark indicating slight pause" , "its use may be divisive" , ", which gives us pause" .)