I thought I had seen this particular butterfly before. It's a modified version of http://www.croczilla.com/~alex/old-site/butterfly.png (see http://www.croczilla.com/~alex/old-site/ for the SVG version which was probably used for this design).

From what I gather, it's an old JASC WebDraw sample (now owned by Corel Draw). I'm going to guess that the original art is public domain (or near it, being a sample graphic), so not too many worries there.

That said, the overall design is well done. Very neat :-)