These small hoverflies are not only pollinators their maggots eat aphids, thrips and scale insects.
I always make sure I have food for the adults in early spring (lots of simple open flowers like Mustard and Allysum) and as my brassicas start seeding there are usually aphids for the pupae. If you have got the right balance your aphids will kick in and a week or so later you will start to see Hover Fly maggots. These guys pupate in the ground so I always make sure I ave food sources I can leave in place for a while.
