I live in a very old stone cottage which butterflies find ideal for spending the winter in hibernation.
Last year I had three, all small tortoiseshell. For the first few days they moved around the house. I thought they might be looking for a cool place. Over the last few days I found all three and placed them on a log and put them in a gauge covered box. Two looked fine and one looked ragged.
In late March this year, I put them in the greenhouse in their box and I visited each day. The third week in March was mild and sunny and one was flying well. It stayed in the greenhouse for two days before leaving for good. Two days later another did the same, but, the third was dead. Yesterday I found a small tortoiseshell in the hallway clinging to the metal window frame like last years. I found a piece of tree wood, but, on my return the butterfly had disappeared. I found it a few hours later and it is now safely housed for the winter. I have a big note on my calendar to move it in mid March .