Ive started to find big black house flies in my house that I haven't seen before. Initially I suspected that they came in when the door was open but we have been keeping the door shut all the time now and new ones keep coming in. We also saw a few outside insects in the house that we would normally never see.
I have tried to find whether there is any open window but there is none. Any idea what can i do to find the source of these flies?