It looks like a syrphid larva and it is feeding on aphids. That tail appendage puzzles me; I haven't seen one like it in other syrphid larvae. Perhaps the spiracles are unusually long and they appear as just one although they are a pair. I wish that more detail were visible.

In Immature Insects several illustrations of the larvae in Syrphidae have posterior spiracles with a tube-like projection and it is described as occuring in many terrestrial species (Its much larger in aquatic species, they actually have a tail) The posterior spriacles are fused or very close together in all syrphids, so if you were to look at the tube straight on (and probably under more magnification) you'd see the pair of spiricles.