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Hi,
A few years ago, we regularly spent a few spring days in Františkovy Lázně (Czechia), and every time I encountered a small dark Dolichopodid there, which turned out to be Achalcus. Now I checked all relevant threads in the forum archive, and learned from Igor's key (https://diptera.i...Europe.pdf) that it must be A. cinereus or A. thalhammeri. The latter (rather rare) species, which is recorded from Bohemia, has whitish-yellow sternites and dark bristles on thorax and abdomen. I'd like to show you a series of pictures from two years with added notes on the characters of the more frequent A. cinereus. I strongly suspect that the animals I have observed are A. cinereus. Confirmation or correction is highly appreciated!
Thanks in advance, Sundew

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This is a specimen from the nature reserve Soos 6 km northeast of Františkovy Lázně. The moorland is famous for its natural mofettes and mineral springs.

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Dear Claudia (?),
All specimens in your pictures are definitely belonging to A. cinereus: the antenna in the male is partly pale, while it is entirely dark in the female. For identification purposes, see also: Pollet, M. (2005) Systematic revision of Neotropical Achalcus and a related new genus (Diptera: Dolichopodidae, Achalcinae) with comments on their phylogeny, ecology and zoogeography. Zoological Journal of the Linnean Society 143: 27-73. With 27 figures. And keep on searching for Achalcinae in Europe, the remain quite special here. Cheers, Marc

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Thanks a lot for confirmation, dear Marc.