Fly screen for panel of bifold doors?

[IhearyouClemFandango]

We have large bifolds at the back of our house, we mainly just have one panel open day to day. I've been looking for a fly screen, just for that main panel. The main ones that I can see velcro on around the frame, which obviously would cause a problem when the whole thing was to be opened. The only way I can see it working would be a retractable one with magnets at the sides, but I can't see anything like that.

This can't be an uncommon problem I'd have thought, has anyone seen anything/got any ideas?

I live on a dairy farm, so it's cowshit and flies gallore.

They have these attached to the outside of some of their farm doors:

https://www.streme.co.uk/product/fly-screen-chain-curtain-diy-kit?gad=1&gclid=Cj0KCQjwjryjBhD0ARIsAMLvnF-fTf7_1jXWkk86wxnsDVBvoZ8qeO7Ky2FEQSgTJQx9GsAEtudiKr4aAgj_EALw_wcB

My landlady said they have blue ones because flies don't like blue (makes them think they're going to drown?) but then in summer the bastard things were still swarming the blue lid of our recycling bin, so I don't know how true that might be. Personally I think I'd prefer one you can't really see, so silver.

I've got exactly the same situation and we were just talking about getting a beaded curtain type affair last night. I'll have to look at how they are put up though as we have blinds.

I've had proper screen doors before when we lived in another country and I don't see how the Velcro ones would be any good.