A flystrip works perfectly! However, it's really disgusting to throw it out after all bugs are just dead and glued to the thing.
http://news.bbc.co.uk/2/hi/science/nature/7586868.stm They think the fly's ability to dodge being hit is due to its fast acting brain and an ability to plan ahead. High speed, high resolution video recordings revealed the insects quickly work out where a threat is coming from and prepare an escape route. The research suggests that the best way of swatting a fly is to creep up slowly and aim ahead of its location. The study has been published in the journal Current Biology. Most people will have experienced the curiously frustrating sensation of carefully attempting to swat a fly, only to swing and miss while the intrepid insect buzzes off to safety. Over the years there have been different theories put forward to explain the fly's uncanny ability to outwit our whacking endeavours.