#1
Moscow region, 31 aug, 2,5mm
S. stagnalis?
It sits on leach with some reason or without?
#2
Scatella tenuicosta - very similar to
stagnalis, but the most distal spot in the wing is shaped like an hour-glass (or Coca-Cola bottle

). In
stagnalis this spot is more oval. All
Scatella feed on diatoms and desmids, so there's no reason for it to be on a leech - perhaps it's just a good place to view the crowd. (The male is on the leech, the female on the leaf.)
#4
I should point out that not all
tenuicosta show the "waisted" spot. Some of them have a less obvious triangular spot, but in all the specimens I've seen, the spot widens anteriorly (towards R4+5). In
stagnalis the spot can also be various shapes but never widens anteriorly.
And don't forget there are other species with which they can be confused

though these two are the most common and widespread.
