This is in Wroclaw, Poland.
I'll be here a few months and I've noticed that they come in large groups in the evening. They are everywhere outside, but I haven't seen any inside. They seem to live in colonies because when you see one, there are 50 others next to it, all sizes (age I guess), but always the same type.
The large ones have body about 1-1.2 cm long but the colonies have some significantly smaller with them, like 1/4 of the size.