# Do Bags of Water on the Ceiling Keep Insects Away? If So, HOW? **URL:** \ **Category:** Factual Questions\ **Created:** [January 6, 2015, 8:13pm UTC](https://boards.straightdope.com/t/do-bags-of-water-on-the-ceiling-keep-insects-away-if-so-how/709154 "2015-01-06T20:13:51Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![astorian](https://avatars.discourse-cdn.com/v4/letter/a/ad7895/32.png) [@astorian](https://boards.straightdope.com/u/astorian)\ **Post date:** [January 6, 2015, 8:13pm UTC](https://boards.straightdope.com/t/do-bags-of-water-on-the-ceiling-keep-insects-away-if-so-how/709154/1 "2015-01-06T20:13:51Z")
Every so often, here in Texas, I’ll come upon a bar, cafe, or Mexican restaurant with an outdoor deck that has Ziploc bags filled with water taped to the ceiling. Whenever I’ve asked what they’re for, I’ve been told that these bags keep mosquitoes and flies away. SOMEBODY obviously thinks that works, though I’ve never noticed a decreased insect population at joints that have these water bags. So, can anyone explain: 1. DOES this actually work as an insect repellent? (I’m extremely skeptical, but I’ve been wrong before.) 2. How is it SUPPOSED to work? What is there about a plastic bag full of water that’s supposed to keep flies out? ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [January 6, 2015, 8:16pm UTC](https://boards.straightdope.com/t/do-bags-of-water-on-the-ceiling-keep-insects-away-if-so-how/709154/2 "2015-01-06T20:16:32Z")
Mythbusters tested this one. They found it had no deterrent affect and might even have a mild attractive effect. ---
**Author:** ![fiddlesticks](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fiddlesticks/32/18129_2.png) [@fiddlesticks](https://boards.straightdope.com/u/fiddlesticks)\ **Post date:** [January 6, 2015, 9:25pm UTC](https://boards.straightdope.com/t/do-bags-of-water-on-the-ceiling-keep-insects-away-if-so-how/709154/3 "2015-01-06T21:25:35Z")
The theory behind the bags as a repellent was that the refracted light from the bags confuses insects’ compound eyes, if I recall the Mythbusters episode correctly. ---
**Author:** ![astorian](https://avatars.discourse-cdn.com/v4/letter/a/ad7895/32.png) [@astorian](https://boards.straightdope.com/u/astorian)\ **Post date:** [January 6, 2015, 9:28pm UTC](https://boards.straightdope.com/t/do-bags-of-water-on-the-ceiling-keep-insects-away-if-so-how/709154/4 "2015-01-06T21:28:35Z")
> [@fiddlesticks](#): > > The theory behind the bags as a repellent was that the refracted light from the bags confuses insects’ compound eyes, if I recall the Mythbusters episode correctly. Okayyyy… sounds like strange reasoning, but it’s some kind of reasoning nonetheless. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [January 6, 2015, 9:45pm UTC](https://boards.straightdope.com/t/do-bags-of-water-on-the-ceiling-keep-insects-away-if-so-how/709154/5 "2015-01-06T21:45:45Z")
previously on SDMB > **[Does a hanging plastic bag full of water actually do anything to deter flies?](https://boards.straightdope.com/sdmb/showthread.php?t=621526)** > > 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... > **[Water and Flies](https://boards.straightdope.com/sdmb/showthread.php?t=654991)** > > Snopes wimped out on this. Anyone know it it works? Ziplock Bag Good Tip for flies ZIP LOCK BAG - Good tip! We went with friends to a restaurant on Sunday for lunch and sat in the patio section beside the store. We happened to notice zip lock... > **[Does a penny in a bag of water repel flies?](https://boards.straightdope.com/sdmb/showthread.php?t=213623)** > > All around Memphis, I have seen places, mostly restaurants, hang a baggie filled with water and a single penny in the bottom, typically near doors and windows. When I asked about this peculiar arrangement, I was told that this was done to repel... ---
**Author:** ![DrCube](https://avatars.discourse-cdn.com/v4/letter/d/a3d4f5/32.png) [@DrCube](https://boards.straightdope.com/u/DrCube)\ **Post date:** [January 6, 2015, 10:36pm UTC](https://boards.straightdope.com/t/do-bags-of-water-on-the-ceiling-keep-insects-away-if-so-how/709154/6 "2015-01-06T22:36:03Z")
[Cecil said](http://www.straightdope.com/columns/read/1956/whats-the-purpose-of-bags-of-water-hanging-in-restaurants) it works. Because flies are skittish types and the water refracts light, causing flies to think there is more movement in the area than there is. Can’t vouch for it though. I learned this trick from Cecil and never used it. I prefer to just have a fan going for outdoor gatherings. EDIT: Oh, never mind. It wasn’t Cecil. Just **Doug**. ---
**Author:** ![Toastmaker](https://avatars.discourse-cdn.com/v4/letter/t/74df32/32.png) [@Toastmaker](https://boards.straightdope.com/u/Toastmaker)\ **Post date:** [January 7, 2015, 7:54pm UTC](https://boards.straightdope.com/t/do-bags-of-water-on-the-ceiling-keep-insects-away-if-so-how/709154/7 "2015-01-07T19:54:02Z")
This is a very common thing to see in Mexico, where loads of “old wives tales” are believed in. Especially in warm sub-tropical and tropical regions, you’ll see them everywhere. I lived there for quite a while. . I don’t think they work at all. ---
**Author:** ![Earl\_Snake-Hips\_Tucker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/earl_snake-hips_tucker/32/3269_2.png) [@Earl\_Snake-Hips\_Tucker](https://boards.straightdope.com/u/Earl_Snake-Hips_Tucker)\ **Post date:** [January 7, 2015, 8:02pm UTC](https://boards.straightdope.com/t/do-bags-of-water-on-the-ceiling-keep-insects-away-if-so-how/709154/8 "2015-01-07T20:02:44Z")
> [@DrCube](#): > > EDIT: Oh, never mind. It wasn’t Cecil. Just **Doug**. BTW, That’s [Doug Yanega](http://www.discoverlife.org/who/CV/Yanega,_Douglas.html), who knows his bugs. I’m surprised that he would post something unsubstantiated like that. ---
**Author:** ![F.U.Shakespeare](https://avatars.discourse-cdn.com/v4/letter/f/aca169/32.png) [@F.U.Shakespeare](https://boards.straightdope.com/u/F.U.Shakespeare)\ **Post date:** [January 8, 2015, 10:12pm UTC](https://boards.straightdope.com/t/do-bags-of-water-on-the-ceiling-keep-insects-away-if-so-how/709154/9 "2015-01-08T22:12:32Z")
Checkpoints in Iraq sometimes had bags of clear liquid hung up, which were invariably filled with dead flies, sometimes gobs of them. Unlike in the staff report, it would appear that the liquid attracted the flies and drowned them. Could the substance be water impregnated with some other substance, say, sugar?