I have to confess, I had never heard of using bags full of water (or in our case condoms) to repel flies before and only after doing a little bit of Googling, it’s apparently quite common. It may be an old wives tale as I don’t think there is any scientific proof that this actually works but many people swear by it.
Using Water to Deter Flies
The idea is that you hang a clear freezer or carrier bag of water outside your door or inside your Polytunnel (in this case) and it will/should scare flies away. Some claim water bags keep all kinds of flying insects away but most report success with houseflies.
How does hanging a bag of water repel flies?
Well, the best explanation I could find is that the way water reflects light upsets the flies. Our little buzzing, annoying friends have compound eyes (1000’s of lenses). This doesn’t give the fly super-duper eyesight it simply means it can detect movement incredibly well and the reason they are so challenging to swat.
A simple bag full of water reflects light in all directions and some insist the flies perceive the clear liquid as the surface of a body of water. Others claim the insect flies away at the sight of its own magnified reflection and or could perhaps mistake the bag for a wasp or hornet nest. That’s about it really. Not convinced? You’re not alone. It’s worth a try anyway!
We had a very entertaining afternoon experimenting anyway. We were waiting for the rain to stop after all!
Originally posted 2015-07-30 09:00:00.
Sean Barker is the MD of First Tunnels, and is enthusiastic about providing quality gardening supplies to gardeners across the UK