Episyrphus: Britain’s commonest hoverfly, commonly known as the Marmalade. This is an extremely variable species whose background colour is highly influenced by the temperature at which the larvae developed. Larvae in hot conditions produce adults with more orange markings (sometimes almost lacking any black markings), whilst those that developed in cooler conditions produce darker adults (sometimes completely black). The larvae feed on a wide range of aphid species and can be very numerous in agricultural crops, for example feeding on cereal aphids and Cabbage Aphid.

Quoted from, Britains Hoverflies by Stuart Ball and Roger Morris (WILDGuides)