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I have to confess that I had never heard of using bags of water to repel flies and only after doing some research realized it is actually quite common in some parts of the US. This is a bit of an old wives tale as there is no scientific proof that this works. That said, with so many people swearing by it, it may have some effect on the flies.

The idea is that you hang a clear freezer bag of water outside your door and it will scare flies away from your home. US restaurant owners use this as well to try and reduce the flies that like to lurk around bins etc. So how is it working? The best explanation I could find is that the way water reflects light upsets the flies. Our little buzzing friends have compound eyes, which means that they have around 8000 lenses. The doesn't give the fly great eyesight but means it can detect movement really well (which is why they are so hard to swat). A bag of water reflects light in all directions and the flies could perhaps mistake the bag for a wasp or hornet nest. The fly would want to avoid these insects as they like to eat flies. Perhaps someone could do an experiment to show that it really does work. You could put one of those sticky pad fly traps in a particularly fly prone area and count how many flies you catch. If you hang a bag of water up next to a fly trap someone else you can see if the number of flies caught is reduced when the bag is present. You should do it in several areas and repeat it several times before you can be sure of your results.

Food and drink
Why does asparagus make wee smell?
Why do beans make you fart?
Why does corn come out like it went in?
How does jello work?
How do they get the fortune in the cookie?
What are the crystals in cold vodka?

Health and disease
Can getting cold give you a cold?
What causes a hangover?
Why does my eye twitch?
Why are allergies increasing?
Do we age in space?

Human nature
Why are horror films scary?
Do dogs find things funny?
Why does an itch, itch?
Why do men have nipples?
Why do papercuts hurt?
Why do we sneeze?
Will my eyes fly out if I sneeze?
What causes sneezing fits?
How does stomach acid work?
Why do we like to eat different things?
Is tongue rolling hereditary?
Why is yawning contagious?
Why does poo smell?

Animal kingdom
Do animals suffer from allergies?
Do badgers cough?
Can you whistle for a bat?
Why can bumblebees fly?
Why don't mice like cheese?
Why is chicken pox called chicken pox?
Can chocolate kill dogs?
Why does a bag of water repel flies?
Do hedgehogs like milk?
Why do you never see baby pigeons?
Why are there no tricoloured cats?
Why do some cats have extra toes?
How do fish end up in volcanic lakes?

The laws of physics
Why is the sky blue?
How come boiling water becomes ice on a cold day?
How does gravity work?
Why does boiling water make a noise?
Why does hot water freeze faster than cold?
What causes rainbows?
Why are clouds white?
Why does helium make your voice squeaky?
Why does the horizon moon look so big?

Bits and pieces
Why are there dimples in golf balls?
Why do Polo mints have holes?
Why does spaghetti break into three pieces?
Why are kitchen sponges so smelly?
How do they get the stripes in toothpaste?

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