This time of year, I love all the traditional themes of spring! Here are some ideas/inspiration for a butterfly theme! Don't forget about this (here) older - but still fresh! Frosting for a butterfly theme.
This setup is so darling - I love how the paper butterflies are used around the table and as if they are flying up from the table! Source
Create a butterfly mobile - you can even hang one on each side of the party table to frame. Source and tutorial found via designdazzle blog
Wrapped candy boxes with a butterfly detail served up in fake grass - Adorable! Source
Butterfly details can adorn any favor... coordinating paper wrapped around playdough containers and a few gems added to the body of the butterfly make these a perfect take-home! Source
Add butterfly candies (see some here or here) or cut out of fondant and add to desserts...