Flies - where did they come from?

[kezza1973]

Last week I came home on a sunny day to find the underside of the plastic carport roof swarming with flies, like regular house flies but smaller. Should I be looking for something dead nearby with maggot shells? This wasn't a normal amount, there were thousands, in fact I had to use another door to get in! Gross.

[Thunderbird+]

I've seen these in my garden too, they seem to be attracted to any warm surfice and they have normally gone by the following day.
I dont know what they are but the swarms seem harless. I think storm flies are smaller and bite.
I dont think you need to dig up the patio either!