To attach the butterfly to a block, I like to stitch down just the body using bullion knots, actually forming the body out of the rows of bullions. I did two browns, then a black, two browns, etc., but you could do whatever combination you like.
Keep stitching until you come to where the body should end; usually the print on the fabric will show that. I ended off the tip of the abdomen with French knots, alternating brown and tan.
Next I added a couple of large iridescent beads for the eyes...
...and some antennae and legs. The wings will lift up off the block, especially if you pin them together for a time.
Kerry L. also uses this method, and has added her own twist; she often does each wing separately, and attaches them to the block and each other with the body stitching. This is something you could do if you find a butterfly print fabric in which only one side of the butterfly wing is shown. Some of the butterflies in the fabric I used are printed this way, and I've used that method too.
I'd also like to try this method just using a printed fabric or batik. One could cut out the butterfly shape and stitch it and turn it just like described here. It would be a butterfly like never existed in nature, but it might be fun!