Fly repellent: bag of water?

I have just come across the mailbag article What’s the purpose of bags of water hanging in restaurants?

I seem to recall a discussion on the boards about the article, but I can’t find it now. I recently came across the hanging bags of water while visiting relatives, and wondered if there had been any breaking research on this subject since 2001.

My own thought is that there’s no way in hell this could actually work, since a fly has no qualms about landing amidst glasses of water on my table, so how could it possibly be bothered by a bag of water 15 feet away? The article here seems pretty credulous about the idea, and cites no sources at all. It would seem to me that with such an implausible mechanism, and not any information showing it works (at least none cited), this idea has to go into the provisional dust bin.

Well there is this:,1785,HGTV_3580_1381705,00.html (nobody knows).

and this (inconclusive)

Hmmm . . . somehow not very satisfying . . .

Weird. I was just at a party over the weekend where the host had several of these around. I hadn’t heard of it before and assumed that it couldn’t possibly work. Never occured to me to check here.

They had a slight variation in that they said you needed to put a penny inside the bag as well. Dunno what difference that would make.

What I’ve been told is that there must be a coin in the bag (penny or quarter, can’t remember which) and that the bag must be hung at the edge of the area. Flies won’t go past it because they think it’s a spider and web, so once you’ve got them shooed out of the area they won’t return. (If there’s a lengthy run of open space, you hang them every couple yards or so.)

I haven’t tested it myself yet but the places I’ve seen it used were fly-free, even with open windows and doors.