During the past couple tests I have been paying close attention to the lifespans of my butterflies in my home. I have concluded that if you own enough milkers that you can empty them out before they are filled (so that they are able to constantly milk the butterflies) those butterflies will "ascend to a higher plane" three days after they were hatched. They will live longer if your milkers reach maximum capacity for awhile before you come back to collect. I had 3 milkers in my home with 4 butterflies at any given time (replacing them as they vanished), and played enough during this last test to empty out all the milkers long before the 2nd one ever filled up. Every single one of my butterflies died 3 days after I created them.
I understand that at least one of the reasons for making this happen is to clear out over-crowded streets. If this is the case, it's not serving its purpose: since we can't put milkers in streets, those butterflies aren't affected much by this. It's the homeowners that have them in their yards that are being punished. Their lifetimes are so short now that it seems pointless to even name them. It adds insult to injury that butterflies that "ascend" due to overcrowding leave behind milk bottles, but ones that "ascend" due to over-milking do not.
I would be happy if the lifespans were doubled. 6 days or so with constant milking by milkers seems much more reasonable to me. I also rather enjoy having to replace them with new hatchlings, but not every 3 days. Also, different rules for houses vs. streets would be helfpul: make the limit on total number of interactions less than it is now in streets, and greater than it is now in homes.