At this time of year, if you find a butterfly fluttering on the inside of your window, it will probably be either a peacock (Aglais io) or a small tortoiseshell (Aglais urticae). It will have come in during the autumn looking for a cool, dark and sheltered place to overwinter and the gap behind the wardrobe in your bedroom must have seemed just right.
But by now, you have turned the heating on and your visiting butterfly has woken up thinking that spring has come. Despite the hostile weather outside and the almost total lack of flowers in your garden, it is trying to leave through the closed window to go about the business of feeding, finding a mate and laying eggs. What to do?
The best solution is to find the butterfly a more suitable place in which to resume its hibernation. Very carefully, catch the butterfly and put it into a closed container (a shoe box is ideal) and leave it in a cool dark place for half an hour or so until it has calmed down.
When the butterfly has settled, place the box in an unheated garden shed, porch or a garage, remove the lid and go away. The butterfly will manage better by itself at this point. If you have neither a shed or a garage, an unheated room in your house will serve: a spare bedroom or a storage room. Remember, though, that your visitor will need to be able to escape in the spring.
If none of these options is available to you, try to keep the butterfly calm and contained until you can release it outside on a sunny day. The falling temperature at the end of the day will trigger the butterfly to look for a more suitable place to hibernate than your wardrobe.
Butterfly numbers are falling; we must help in any way we can.
Header image by Clive Knight
Southwick Country Park Nature Reserve 
Well written and great info. Butterfly numbers are collapsing. We need to do everything we can to protect them.