Scaeva pyrastri is a relatively large hoverfly with distinctive comma-shaped markings on a black ground on its abdomen which give it its common name of the Pied Hoverfly. Although on the wing in the UK typically from about April to September, they are at their most numerous during high summer.
Ball and Morris (2105) state that it is a migratory species that arrives in Britain in highly variable numbers from year to year. It is widespread, but scarcer in the uplands.
The specimen shown above is a female as indicated by the widely-spaced eyes.