No interactions present.
Is the photo showing the fly on a rock? If so that would be entirely appropriate, as for many species their larvae attach on to rocks in running water, filtering organic matter from the passing water.
For info on blackflies see:
Entomologist and biological recorder
Hi, yes the fly was on a rock close to a woodland stream , thankyou, regards Keith.
Lat/Lng: 52.9704, -3.168
OS grid ref: SJ216420