I admit that I just never do anything to mine because I don't want them to die, and like Enola I've had mine since I got my house/got the skills to make eggs and hatch them.
As for the achievements, I'd rather get them for releasing butterflies into the wild. I get attached to my little pixel animals darnit.
I have 14 butterflies and kind of want them to die. D; I have a milker, but don't milk them by hand. Does the milker have the same effect on their life span?
Yes it does as far as I know Coi Koy but some people milk them as well as letting the milker do it which means they expire faster. I let my milker fill up then leave it full until I get desperate for milk which has happened about once or twice. I also massage my butterflies without milking them just to keep them happy :)
Interesting, Xyrem. I only ever get 2 to 3 milk bottles from mine (if anything). Maybe I should start massaging them to see if it's related... I'll start that today.
By the way, unless they changed it since then, I was told by a dev that all interactions with a butterfly shorten its lifetime, including singing/massaging.