There is a post on here for a wasp trap. My husband took that idea and played around a little with it. He used a clear two liter bottle.
it has to be clear!! he used colored koolaid since they do not like clear sugar water. they think of it as a hornets nest. and instead of putting dead wasp in the funnel he put raw bacon or lunch meat in the water.
he has caught a bunch of flies this way out at the barn. they start to hit it about twelve hours after he put it up in the shade. probably would hit sooner in the heat.
that way the meat started to smell. he had an inch of flies in it in no time.
i just want to thank the person who posted the wasp trap idea. they work too. now i :smt023 do not have to buy that spray to kill them with.