Tiger Swallowtail on White Clover.  The lawn care companies and chemical outfits will tell you this  

" weed" should go-not if you like butterflies.  In a 15 minute walk thru white clover on our lawn I saw 7 species of butterflies and numerous bee species.  A "clean" lawn may look good but provides no food for most of natures wonders. We do not even mow for a while the white clover is in bloom.