Xylota sylvarum is a sleek black hoverfly with a bright yellow tip to the abdomen.
The hind tibiae are black for the apical two-fifths, in contrast to the very similar Xylota xanthocnema which usually doesn't show (much) black on the hind tibiae. 

First 4 photos: A female. Gagelbos, Utrecht, The Netherlands, 24 July 2018
Last photo: A male. Kievitslanden, Zeewolde, The Netherlands, 17 September 2019