This is another question that I get relatively often, "If I touch a butterfly's wings will it die?"
The answer to this question is "NO!" I have touched the wings of tens of thousands of butterflies over the years and have yet to kill one, although some like to play dead. Although, I do try to discourage people from handling butterflies by the wings if it is not necessary.
In some activities with butterflies you have no choice but handle a butterfly's wings. For example, when tagging a monarch butterfly you have to touch their wings to accomplish the task. When I move butterflies from one location to another in my job, I have to handle them by the wings. I cannot trust the butterflies to fly behind me and follow me from one room to the other.
What is at issue is the tiny scales, technically modified hairs, that cover a butterfly's wings. These scales provide rigidity to the wing that allows a butterfly to fly. These scales also provide color to the wing that serves as a warning to predators or as a tool for communication with other butterflies. As example, some butterflies will flash the bright colors on their upper wings by opening and closing their wings. They do this to startle predators or to signal potential mates.
Butterflies lose the colorful scales on their wings with age. As they bump into plants and other things scales are knocked off. The more of these scales the butterfly loses, the less maneuverable the butterfly is and the less effective are things like eye spots and bright signal colors.
While touching a butterfly's wings may not kill it immediately, it could potentially speed up the fading of the colors on the butterfly's wings, wiping out patterns that are used to protect the butterfly from predators. Touching the butterfly's wings could potentially result in a shorter than expected life. If it's not necessary than why do it, at least from the butterfly's perspective!