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!
Sean Barker is the MD of First Tunnels, and is enthusiastic about providing quality gardening supplies to gardeners across the UK