Brian Gaff submitted this idea :
Unfortunately you cannot have an open back door here without 20 flies and
assorted bugs wandering in then seemingly being unable to remember the way
back out again.
Honestly they need a bigger brain obviously.
Brian

Our back door is always open in this weather, but we have one of those
mesh things, which pulls itself closed with magnets. It was very
effective last year, you could see the flies were queueing up there to
in, but this year there are very few.