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RUS, Magadan reg., 3-4 mm, streams

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Blephariceridae ?

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We (Dmitry Gavriushin and me) thought so. But seems it is not Blephariceridae.
New idea:
Thaumaleidae comprise a homogeneous family of
small (wing length 1.5-7.5 mm) (Fig. 1) stoutly built flies
with shiny yellow to black bodies. Their eyes are
holoptic in both sexes, their antennae short and slender.
The wings have a characteristic venation and tend to
fold downwards across a transverse line of weakness
near the apex of the subcosta. The adults are diurnal
and usually frequent wet rocks or vegetation near
streams in wet forest. The larvae are aquatic and
amphipneustic. The family (about 100 described species)
is possibly mainly holarctic in distribution with less than
a dozen species having been described previously from
the southern hemisphere.

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I feel sure this is a chironomid - most likely Diamesinae. Several species of Diamesa have reduced antennae and enlarged genitalia in the males, and the habitat is right. No doubt John Carr will be able to contribute as well, but I think it's safe to re-title this thread Chironomidae

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Tony, thank you!!!

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The wing is typical Diamesinae, with right angled anal lobe, long, curved r-m crossvein, and short m-cu crossvein intersecting after the fork in Cu. (Maybe it's a crossvein between M1+2 and M3+4 in modern terminology.)

Several species of Diamesa fly in winter in temperate and boreal North America.

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Large legs and genitalia and reduced male antennae are associated with mating on the ground. Cordiform fourth tarsomeres are said to be associated with walking or running.

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Thank you, John!