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Hi Jürgen, I think they are, based on this information (the dark stripe on tibia III is visible on the 2nd image):

on male Bibio johannis:

Een veldtabel voor de inheemsezwarte vliegen (Bibionidae) door Theo Zeegers, 1997
mid April - mid May, antennae: 9 segments, metatarsus slightly thickend, approx. length = width x 3
(excerpt translated by eklans)

BIBIONIDAE DE LA FAUNE BELGE, Jan Verbeke, 1971
wings hyaline, strong brown stigma
flagellum 7 segments
body black, black hairs - including occiput
tibia III yellow, gradually thickened from base to tip, rear surface with brown stripe
metatarsus III thickend
legs I & II predominantly reddish brown to brownish
tibia II yellowish - legs sometimes completely yellowish
(excerpt translated by eklans)

Suomen karvasääsket ja maasääsket (Diptera, Bibionidae ja Pleciidae), Antti Haarto, 2012
Antennae with 9 segments. Colour of hind femora
varies from totally yellow to largely dark brown. Hind
tibia yellow and evenly broadened towards its apex.
Hind tibia with dark stripe of sensillae
Dark specimens have black femora and brown tibia
and therefore the dark stripe of sensillae does not
differentiate. Tarsi yellow.