These things are amazing.  There's something about these jars.  I've tried to use the bait in other containers with no fly catching luck at all.  But I put the jar out with the bait and within hours it starts to collect flies.  It's really disgusting and the only thing I wish is that these were disposable, maybe made of thinner plastic, maybe more like cheap water bottles, because I do feel terrible throwing them away, and I do throw them away, because the idea of emptying them is just awful.