Hi Julfeen,
If you look at
www.epinions.com they have a eco friendly "woodstream fly trap with bait that is supposed to be excellent....but i agree with kilk there has to be either a dead carcus or rotting meat in the vicinity to have an infestation... if you google getting rid of bluebottles you will be inundated with ideas.
Or rentokil offer a free survey on getting rid of bluebottles contact 1890 333 888
Goodluck Summersun