Snail-killing Fly (Sepedon sphegea)
This was one of those 'risky, but ultimately worth it' moments, as I perched precariously on what felt like a very unstable mound of grass, right on the edge of a river, streching to catch sight of what was moving, many feet away, further along the bank, almost out of sight.
I got video too.............
"Sepedon sphegea" is a Palearctic species of fly in the family Sciomyzidae, the marsh flies or snail-killing flies. The larva feeds on aquatic snails and as an opportunist on other invertebrates.