For the last couple of years we have had group of them apparently hibernating in the small gap around our permanently slightly open bathroom window. Must be about a hundred or more of the little blighters and occasionally one wakes up and starts flying around while i am trying to brush my teeth.
Not sure why they choose that spot. The plastic windows don't harbour any obvious signs of nourishment, maybe the steam/moisture from the shower is enough to sustain them, although the one that wake up early and fly around end up dead within a day or so.