I have these tiny black flies flying around in my flat - there are not loads, maybe between 2 and 4 in each room at any time (living room, kitchen and bathroom) and they are driving me crazy. They are really tiny and fly quite slowly so its easy to squash them, but I need to get rid of them! We have no houseplants and never have and there is no fruit lying around - what else can they be? How will I find out where they are coming from? It's December! Surely its too late in the year and too damn cold for flies?!