Hoverfly on Agapanthus
No interactions present.
I think this must be an odd form of Episyrphus balteatus (sorry, mis-spelled Episyrphus in the ID above), which can vary quite a lot. There was a discussion and some more photos of similar dark forms on the Hoverfly Recording Scheme forum last year:
Entomologist and biological recorder
Lat/Lng: 52.0, -0.9
OS grid ref: SP8138