This is my version of a Fruit Fly Trap, but my extreme version of it. After seeing many different kinds of Fruit Fly Traps online, here at the Instructables site, and other places. I came to understand many things.

For example...

1.) Fruit flies are attracted to ripe fruit, not necessarily rotting as some will state, but of course the last being "the" choice for them.
2.) They are very attracted to the scent of Apple Cider Vinegar.
3.) But most, they are rather annoying!

Step 1: Tools and Materials

Tools:

Scissors
X-acto Knife
1/16", or smaller, drill bit tip (toothpick will do).

Materials:

1 - 12 - 16 oz. empty water bottle, ensure that it is dry. Also make sure that you keep the bottle's lid.
One small piece, approximately 2" square, of Food Wrap Plastic.
1" or smaller size of masking tape
Adhesive Spray (Optional)
Approximately 2 - 4 oz. of Apple Cider Vinegar.

Step 2: Putting the Fly Trap Together

Putting the Fly Trap Together

Using your X-acto knife, or scissors, cut around the top of the water bottle right were the bottle bends.
Using small rolls of masking tape, tape the small loops inside the water bottle approximately 2" inches below the top. This is important because the top part of the bottle will rest on the top and if the masking tape loops are too far up the will push the top up and cause an opening. We want to keep the finished trap from having any openings other than in the center (SEE STEP # 4 )
Using the X-acto knife cut a circle around the top of the water bottle's cap. If you have one of those bottles that uses a hard plastic top skip this step. The top is going to be used to act as a ring and hold the Food Wrap Plastic in Place (SEE STEP # 4).
Apply a small 2" x 2" square of Food Wrap plastic to the top of the bottle and secure it with the ring you just created. If you had a hard plastic cap on the water bottle simply apply the plastic around the bottle opening and secure it with the masking tape.
Using a small drill bit (i.e. 1/16" or smaller) poke several holes around the Food Wrap plastic. If you don't have a small drill bit you can use a toothpick to poke the holes. The holes are going to allow the fruit flies to come in but prevent them from coming back out.
On the bottom portion of the cut out bottle put approximately 2 - 4 ounces of Apple Cider Vinegar.
On the top portion of the bottle, where the Food Wrap Plastic is, on its exterior place one coat of Sprayable Adhesive (Optional). This will ensure that the fruit flies that don't fall in the Apple Cider Vinegar will not come out and stay stuck towards the top, either of the masking tape rolls or the adhesive that you sprayed.
Last step is to place the top part of the bottle upside down into the lower chamber of the plastic bottle where the apple cider vinegar is stored and secure it with a couple of turns of masking tape. During this process ensure that there is no visible gaps between the top and bottom of the water bottle trap. If there is, apply a few extra pieces of masking tape.

Once all these steps are complete, simply place in or near the area of concentration, and watch how your fruit fly problems are solved. Once you see that your trap is full you can simply discard the liquid and the fruit flies, and recycle the plastic bottle, and you can create a new one using the above steps again.