Hibernating very early?

[LindaL]

Over the last few years I have had butterflies (usually just one at a time) hibernating in a corner of my bedroom ceiling. Twice before it has appeared there in August. This year I first noticed one on 14 July, and yesterday I realised that it had been joined by another one. I think that they are small tortoiseshells. Are they really hibernating this early? Why would they go into hibernation so early?

Linda