Flies in my polytunnel?

[OverWyreGrower]

We have got some little black flies hanging around in our polytunnel - loads of them actually!

They are at the ends of the tunnel, right up near the top (about 7ft up)...

I can't work out why they are there? As we are currently working on/in the tunnel, there is nothing growing in there, and I can't see anything that would attract them...

We hosed the whole tunnel off yesterday, paying special attention to all the joints etc, and even that didn't deter them!

Any ideas what to do/use etc to get rid of them??

[jackyspratty]

put our poly up yesterday.......full of flies too.....nothing growing in there either....and oursis on concrete too! last year we had similar problem and used those yellow fly paper things, but they catch bees etc too, not good!

[Two_Sheds]

Are they really really black flies with dangly bits hanging down? They're out a bit early this year