In reply to Wsdconst:
If it's fruit flies (the small ones) that are the problem you can make a simple trap for them.
Put some cider vinegar in a bowl (perhaps with some bits of fruit too) and cover it tightly with some cling film. A container where you can secure the cling film with a rubber band is good. Make some holes in the cling film and they will tend to get trapped in there.
Hole size and density affects the outcome. The hole should be bigger than the flies (!), perhaps 2cm between holes, not more I would say. Generally I've found they still have some trouble to get inside but once in they stay. Ok, it's not like I tagged them, but I came to this impression. At least it concentrates them in one place, and after a few hours, or overnight, you can choose what further method (or methods) you would like to apply in order to finally dispose of them.
Videos on youtube.