This might interest some people..
[h=2]I've found a butterfly in my house/garage - what should I do?[/h] Several species of butterfly hibernate in the UK -
Brimstone,
Comma,
Large Tortoiseshell,
Peacock and
Small Tortoiseshell. In recent years, with climate change, we're also starting to see the successful overwintering of
Clouded Yellow and
Red Admiral. Such species tend to look for sheltered areas in which to hibernate, which is why they are sometimes seen in houses and garages. However, an unnaturally warm environment, such as a house that is centrally heated, can be quite detrimental since the butterfly will become active and use up the essential body fats that will see it through the winter. The best thing to do is to be "cruel to be kind". One option is to place the butterfly in a cold and dark environment and out of the way of predators, such as in a log pile, an outhouse, or a hollow tree. Alternatively, on the next sunny day that is sufficiently warm, release the individual outside so that it can find a more suitable location in which to hibernate itself.
Taken from this site, no connections etc....
http://www.ukbutterflies.co.uk/faq.php