We just read a great butterfly book! It is a # 2 and Josh could read it very easily so it is probably around a 1.5 RL (my opinion). If you are studying butterflies or just want a cool science read then be sure to check out A Butterfly Grows (Green Light Readers Level 2) by Stephen R. Swinburne. It tells the lifecycle of the butterfly as if the butterfly was telling the story. The pictures are all photographs and are big and bold.
We loved it!