2nd graders at one of my schools were actually growing butterflies in their classrooms for their science classes. So what a great tie in to do butterflies in art. We discussed symmetry and what it is in art and nature. Students cut out their butterfly shapes by folding a piece of paper in half and cutting on the fold to get the same shape for both wings. When we applied paint, we only did to one side, then we folded the butterfly back together and smooshed the paint around. When they opened up their wings they had a beautifully colored butterfly that was symmetrical in color and shape.
For the background we used tissue paper that bleeds and water. I just learned about this technique this year and love it. Just put tissue paper on your white paper and add water. Let the tissue paper dry, and then it peals right off. I was able to keep reusing the same tissue paper for all my classes.