Small fly on a Hogweed leaf

Small fly on a Hogweed leaf

Observation - Small fly on a Hogweed leaf - UK and Ireland. Description: I saw this small fly repetitively raising and lowering its abdomen in course of feeding (as I presume) on the leaf surface (Images 1 and 2 show examples). There were also wing movements. See Comment

I saw this small fly repetitively raising and lowering its abdomen in course of feeding (as I presume) on the leaf surface (Images 1 and 2 show examples). There were also wing movements. See Comment