Butterfly about in part of spring (7)
I believe the answer is:
monarch
'butterfly' is the definition.
(monarch is a kind of butterfly)
'about in part of spring' is the wordplay.
'about' becomes 'on' (as in a book 'on' a certain topic).
'in' is an insertion indicator.
'part of spring' becomes 'March' ('March' is part of 'spring').
'on' inserted inside 'march' is 'MONARCH'.
(Other definitions for monarch that I've seen before include "Butterfly (emperor, say?)" , "Eg, king, queen, emperor" , "one over realm?" , "Not a subject" , "Head of State" .)