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First, we cannot see the tip of the front tibiae, which is needed to discriminate between Bibio and Dilophus. In Bibio, the front tibiae end in a pair of large spurs, in Dilophus there is a circlet of small spines. However, the males of the frequent D. febrilis do not have such swollen hind tibiae and tarsi. So it might be a Bibio indeed.
There are two autums species, B. longipes and B. clavipes (see https://www.flick...177500145/). B. clavipes has a rather pale stigma that does not extend into the tip of the costal cell; I saw it in Brandenburg recently. In your case, I would vote for B. longipes.
Maybe Theo can say more.
Regards, Sundew