I recently built a non-chemical fruit fly trap and I have had some success reducing the number of fruit flies buzzing around my place, so I thought I should share it with you all.
I made the trap because I was suffering from an overload of fruit flies around my worm farm. I have been known to overfeed my worms and give them too many fruit scraps, creating a perfect environment for fruit flies to breed in. This didn't really bother me except for the cloud of fruit flies that would swirl around my head when I opened my worm farm.
After a quick internet search, I discovered vinegar is a solution that fruit flies are attracted to. Makes sense really, since vinegar is similar smelling to the rotting fruit in my worm farm. I then just had to find a suitable container to hold the vinegar, whilst also not attracting my toddler to tip the vinegar everywhere or minimise the amount spilt if she did decide to tip the container upside. My solution was an old plastic "jar". I filled the bottom of the container with white vinegar (about 1/10) and then drilled some holes in the lid. The holes were large enough for the fruit flies to fly in. I then just sat this container on top of my worm farm. Voila!
With this solution I have definitely managed to reduce the number of fruit flies in and around my worm farm. There are still some fruit flies floating around, which is just because I still have rotting fruit in my worm farm, but certainly numbers have decreased significantly and not worrying me at all.
This system does require some maintenance, but not very much though. I have to replace the vinegar every 2-3 weeks. I just chuck out all of the old vinegar and dead fruit flies and then add new white vinegar in the bottom of the container. This is cheap solution and has minimised my environmental footprint, as I have used products around my house (old container), will require very little input over time (just the new white vinegar) and uses no harsh chemicals. No off the shelf product required for me. Hope this solution works for you as well!