Parasitized flies?

Parasitized flies?

Observation - Parasitized flies? - UK and Ireland. Description: I found 6 of these flies attached to a grass seed head in damp woodland.One was just about alive the others were dead. Two of them were only shells .The other four had large bulging abdomens which I now think may have contained a parasitic grub but I did

I found 6 of these flies attached to a grass seed head in damp woodland.One was just about alive the others were dead. Two of them were only shells .The other four had large bulging abdomens which I now think may have contained a parasitic grub but I did not look closely at the time and the photos are not very good.Are their abdomens split open or is it just a white stripe and my imagination.