Propane-powered Mosquito Traps: What's the deal? Do they work?

I've got nothing against bats, and wouldn't mind if there were bats flying around my place at night (there might very well be - I don't know

- it's hard to see when it's dark out).

But it's a fallacy that bats eat lots of mosquitoes.

I have no doubt that in more tropical or sub-tropical areas, rural, lots of standing water, marshes, etc, that there are clouds of mosquitoes where the bats can just fly around with their mouths open and collect dozens of mosquitoes in a single pass and repeat that several times a minute for several hours.

But in the northern half of the US and southern Canada, in urban or even suburban residential back yards, you're not going to have these dense clouds of mosquites and large open flyways for the bats to swoop in with their mouths open and collect them.

Individual mosquitoes are too small to be detected by the bat's echo-location system, and a single mosquito wouldn't give the bat enough calories to make the effort worth it.