J.B.
Well I think it is good to explain not to harm innocent creatures, but I think what you did was perfect. He probably was just investigating and wanted to see what would happen and did not fully get that it was something terrible for the butterfly. I mean, he probably doesn't even associate death with pain at this point and he certainly has no fear of death or sense of his own mortality. So, I think he was a being a boy and explaining that ripping off the wings hurt the butterfly was perfect. Also continuing to show him how to be gentle with living things is important. My three year old tends to man handle my six month old and I always remind him that my six month old is a living human and has feelings, he is not a doll or toy. I don't think there is any worry here, if a young child more like 10+ starts harming kittens etc, then it's big stuff. But such a young child was probably merely curious and doesn't have much empathy yet. You did fine and your kid is normal!!:D