# Does a hanging plastic bag full of water actually do anything to deter flies? **URL:** \ **Category:** Factual Questions\ **Created:** [August 23, 2011, 5:20pm UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798 "2011-08-23T17:20:22Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![Phlosphr](https://avatars.discourse-cdn.com/v4/letter/p/c68b51/32.png) [@Phlosphr](https://boards.straightdope.com/u/Phlosphr)\ **Post date:** [August 23, 2011, 5:20pm UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/1 "2011-08-23T17:20:22Z")
I was at a restaurant last evening in Boulder, CO and saw several plastic bags half full of water hanging from the outdoor porch, a couple inside and a few back by he kitchen. When I asked, the waitress said, they help keep the flies down in the dining room. So naturally, I asked how…she did not know. Has anyone seen these before? Does anyone know if they work? And if so, how? ---
**Author:** ![hende](https://avatars.discourse-cdn.com/v4/letter/h/aca169/32.png) [@hende](https://boards.straightdope.com/u/hende)\ **Post date:** [August 23, 2011, 5:34pm UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/2 "2011-08-23T17:34:11Z")
For what it’s worth… [MythBusters](http://dsc.discovery.com/fansites/mythbusters/db/animals/repel-flies.html)says it doesn’t work. [Snopes](http://www.snopes.com/critters/wild/flies.asp)says it is undertmined. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [August 23, 2011, 5:40pm UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/3 "2011-08-23T17:40:07Z")
[Straight Dope Science Advisory Board column](http://www.straightdope.com/columns/read/1956/whats-the-purpose-of-bags-of-water-hanging-in-restaurants) on this question. One previous [thread](http://boards.straightdope.com/sdmb/showthread.php?t=617598). (I think there are additional ones as this comes up from time to time.) ---
**Author:** ![AuntiePam](https://avatars.discourse-cdn.com/v4/letter/a/f19dbf/32.png) [@AuntiePam](https://boards.straightdope.com/u/AuntiePam)\ **Post date:** [August 23, 2011, 5:50pm UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/4 "2011-08-23T17:50:20Z")
Snowbird neighbors came back from Florida and recommended it – said it worked for them down there. It didn’t work for us. Some days there were no flies, other days they held conventions. The only thing that’s guaranteed to keep flies away from our deck is a nice breeze. ---
**Author:** ![R.P.McMurphy](https://avatars.discourse-cdn.com/v4/letter/r/7993a0/32.png) [@R.P.McMurphy](https://boards.straightdope.com/u/R.P.McMurphy)\ **Post date:** [August 23, 2011, 6:01pm UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/5 "2011-08-23T18:01:59Z")
Not very well according to my favorite, down to earth, unscientific, practical guide to buying shit website: [http://www.kfvs12.com/story/15149152/does-it-work-home-remedy-for-distracting-flies](http://www.kfvs12.com/story/15149152/does-it-work-home-remedy-for-distracting-flies) ---
**Author:** ![mac\_bolan00](https://avatars.discourse-cdn.com/v4/letter/m/b3f665/32.png) [@mac\_bolan00](https://boards.straightdope.com/u/mac_bolan00)\ **Post date:** [August 24, 2011, 5:49am UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/6 "2011-08-24T05:49:38Z")
whenever termite larvae mature and they start swarming around ceiling lights and streetlamps, some people would tape an empty cellophane bag from a cigarette case on their ceiling bulbs. immediately, the swarming insects fill it up and can’t get out (their wings shear off.) soon you’re holding a plastic bag full of icky wingless insects. they don’t really harm people and they will soon fall prey to bats anyway but i saw that the method was effective. while in the mines, we had a lot of buzzing insects at night. they’re neither flies nor mosquitos; just harmless bugs and beetles. i tried the same thing using a big plastic bag this time. sure enough, it filled with insects in a short while. i debated on whether or not to set them loose but the crowd prevailed over me and i committed one of my many animal geneocides. mythbusters can be seriously wrong at times. ---
**Author:** ![EvilTOJ](https://avatars.discourse-cdn.com/v4/letter/e/ee59a6/32.png) [@EvilTOJ](https://boards.straightdope.com/u/EvilTOJ)\ **Post date:** [August 24, 2011, 5:53am UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/7 "2011-08-24T05:53:53Z")
An empty plastic bag is not the same as filling one with water and putting a penny in it, as stated in the OP. ---
**Author:** ![mac\_bolan00](https://avatars.discourse-cdn.com/v4/letter/m/b3f665/32.png) [@mac\_bolan00](https://boards.straightdope.com/u/mac_bolan00)\ **Post date:** [August 24, 2011, 5:56am UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/8 "2011-08-24T05:56:04Z")
yeah, well those geniuses should have tried it empty first. less messy. and half-filling a plastic bag with water and dangling it over people’s heads, and expecting it to stay leak-proof and stable, let alone be useful for anything, would have been too far from my mind. ---
**Author:** ![Gary\_Robson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gary_robson/32/3448_2.png) [@Gary\_Robson](https://boards.straightdope.com/u/Gary_Robson)\ **Post date:** [August 24, 2011, 1:05pm UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/9 "2011-08-24T13:05:37Z")
Are you sure the bags were just water? I use fly traps that consist of a bag of water with a bait pouch in it, designed so flies can get in but not out, and they’re quite effective in trapping and killing the flies. ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [August 24, 2011, 5:16pm UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/10 "2011-08-24T17:16:12Z")
> [@Phlosphr](#): > > I was at a restaurant last evening in Boulder, CO and saw several plastic bags half full of water hanging from the outdoor porch, a couple inside and a few back by he kitchen. When I asked, the waitress said, they help keep the flies down in the dining room. I’d be concerned if the restaurant was depending on plastic bags containing water to deter flies. What other goofy sanitation myths do they buy into? Playing music by Yanni in the kitchen to keep rodents and cockroaches out? You know, that might work… :dubious: ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [August 24, 2011, 5:18pm UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/11 "2011-08-24T17:18:40Z")
Keeps customers out too. ---
**Author:** ![VOW](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/vow/32/3043_2.png) [@VOW](https://boards.straightdope.com/u/VOW)\ **Post date:** [August 24, 2011, 6:04pm UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/12 "2011-08-24T18:04:45Z")
Those commercial fly traps where you add water to the bait inside a plastic bag and then hang the bag out to attract flies…you wouldn’t want to hang those anywhere NEAR people eating. The stench is pukifying! ~VOW ---
**Author:** ![Laggard](https://avatars.discourse-cdn.com/v4/letter/l/9de053/32.png) [@Laggard](https://boards.straightdope.com/u/Laggard)\ **Post date:** [August 24, 2011, 6:14pm UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/13 "2011-08-24T18:14:04Z")
Sounds like a perfect breeding spot for mosquitos. ---
**Author:** ![PapSett](https://avatars.discourse-cdn.com/v4/letter/p/ecc23a/32.png) [@PapSett](https://boards.straightdope.com/u/PapSett)\ **Post date:** [August 24, 2011, 10:56pm UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/14 "2011-08-24T22:56:43Z")
I have had a bag of water hanging outside my back door since this was last discussed, and I will say yes, it has brought the number of flies coming in my back door WAY down. Before, every time I opened the door about a half dozed swarmed in. I bet there hasn’t been a half dozen in TOTAL since hanging it. I am a believer! ---
**Author:** ![chiroptera](https://avatars.discourse-cdn.com/v4/letter/c/df705f/32.png) [@chiroptera](https://boards.straightdope.com/u/chiroptera)\ **Post date:** [August 25, 2011, 11:27am UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/15 "2011-08-25T11:27:00Z")
My neighbor has old CDs hanging in his vegetable garden and by the back door, I just discovered last week. He says it has the same effect as bags full of water in deterring a lot of flying insects because they’re put off by the reflected light. So I hung a couple of old scratched CDs from the little porch just above my back door. Which gets opened repeatedly (four dogs…dogs out, dogs back in, dogs back out…etc.) As PapSett says…it really does seem to work! ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [August 25, 2011, 6:05pm UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/16 "2011-08-25T18:05:23Z")
> [@chiroptera](#): > > My neighbor has old CDs hanging in his vegetable garden and by the back door, I just discovered last week. He says it has the same effect as bags full of water in deterring a lot of flying insects because they’re put off by the reflected light. > > So I hung a couple of old scratched CDs from the little porch just above my back door. Which gets opened repeatedly (four dogs…dogs out, dogs back in, dogs back out…etc.) As PapSett says…it really does seem to work! I seriously doubt that such CDs will deter insects. I _have_ heard claims that they will deter geese, which I find more believable. As for plastic bags ful of water – I haven’t read the link in the OP yet, but it sounds totally unlikely. ---
**Author:** ![Inigo\_Montoya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inigo_montoya/32/124_2.png) [@Inigo\_Montoya](https://boards.straightdope.com/u/Inigo_Montoya)\ **Post date:** [August 25, 2011, 7:06pm UTC](https://boards.straightdope.com/t/does-a-hanging-plastic-bag-full-of-water-actually-do-anything-to-deter-flies/593798/17 "2011-08-25T19:06:58Z")
> [@Jackmannii](#): > > I’d be concerned if the restaurant was depending on plastic bags containing water to deter flies. > > What other goofy sanitation myths do they buy into? Playing music by Yanni in the kitchen to keep rodents and cockroaches out? The OP was in The Peoples Republic of Boulder. Yanni and roaches abound, but the Yanni tends to attract the roaches. 😃