Species Identification - small insect
I think @fileunderwater is definitely right, these are psocids (of the family Psocoptera, AKA booklice). 

Specifically, the body shape looks very similar to that of Dorypteryx domestica or some closely related species. 



See here for an additional photo.

According to this site, the species is present in many countries including Poland.

The source cited at this site (Kučerová 1998) mentions that this species can be brachypterous (i.e., having very reduced wings. I can't tell from the quality of the photo whether your specimens has tiny wings or not. Your top picture looks like it might. 

Citations:

Kučerová, Z. (1998). Wing polymorphism in Dorypteryx domestica (Smithers) (Psocoptera: syllipsocidae). Insect Systematics &amp; Evolution, 29(4): 451-57.