1cm body length,
Hundreds of them crawling on a path (under trees).
Did not fly (yet).
This seems to be a female (as it has smaller eyes and larger wings than the other)
But they are too small for Bibio marsi, although the color and time of the year (23.4. is close to Markus day).
In mixed woodland
Fly parasitizing aphids (aphid record at https://www.inaturalist.org/observations/208443152)?
?