Frugal fly trap

This is a recipe for a frugal home made fly catcher. The one's you buy at the farm stores are smelly and expensive. My home made version works like wonders and is frugal. Here's what you do.
Take one empty 2 litre pop bottle (I like to take the label off but you don't have to)
Insert one banana peel
1 c. apple cider vinegar
1 c. sugar
Fill to where the bottle begins to slope at the top with warm water.
Replace the cap and shake.
Tie a wire or string around the top of the bottle and hang in the branches of a tree. Remove the bottle top and save for when you want to discard the full bottle.
The fly trap will fill and a 3 or 4 inch layer will form near the top, then suddenly it will sink to the bottom and a new layer will form. This will continue until the bottle is full. At which point you can replace the lid, remove from the tree and discard and replace with a new fly trap.
We put these all over the yard in the trees. Its amazing how they work. These are especially helpful if you have barn animals. I have found that these work best if they can be placed in tree branches as opposed to hung on a fence or the like. I don't know why.