They could be Cluster flies and they look for hibernation

spots. Drainage holes in UPVC windows is a favourite place and often if you open the window it’ll unnerve them and they’ll come out into your house. Harmless and I think they’re pollinators so don’t destroy them, just encourage them outside. I’ve also had them in the attic.

Posted By: Chopper, Oct 1, 16:24:48