One of the earliest hatches in the Czech season are a kind of tiny black dipterans that I have so far failed to scientifically place. They are tiny indeed, almost impossible to imitate due to their diminutive size. They are however one of the first hatches to appear, allowing for one of the first opportunities for surface action. I will be expecting them to appear in about a two weeks time.
Here is a fly pattern designed to imitate this insect, tied on the smallest hook I consider practical for actual use - #20 Hanák dry fly. Anything smaller than that is just showing off (unless your name spells Andy Baird; then it would be just normal).
#20 Hanák H130BL hook
14/0 Sheer thread, color grey
#16 UNI tinsel, pearl
2 tips of CDC feather
homemade Muskrat dubbing, dyed black
a light touch of black CD marker to darken the head