The update is that I found him** later in the day in my yard. I put him on some flowers, and he hung out there most of the day. Then he fluttered onto me again and crawled up to my shoulder--and then I thought he'd been blown off again, but later in the evening I found him on the kitchen floor, so I've now set him on some ironing in my study, with a sugar-water soaked towel. Tomorrow if it's warm again, I'll set him back outside, if he's still alive.

... I am doing hospice for a butterfly...

**In the process of all this I've found out how to tell the sex of a butterfly, and this one is a male.