update: The bait is truly disgusting but this is working very well. The trap was made from an artichoke hearts jar, with a little bit of the oil left in the bottom of the jar. And a little bit of wine poured in. It is working spectacularly well. Even though there are ripe apricots waiting to be preserved, and 2 5-gallon crocks of pickles fermenting on the table, there are no fruit flies flying!
Homemade Fruit Fly Trap
1 quart jar
1 piece of paper, rolled up into a funnel
apple cider vinegar
small slice of banana
Fill a quart jar with a 1/2 inch of apple cider vinegar and a small piece of banana. Roll up your paper into a funnel shape (larger at the top) and tape it in place. Place the funnel into your jar and make sure all the edges are secured shut with tape.
You may have to adjust the size of your funnel to make sure it fits nicely into your jar.
Place the jar where the fruit flies are flying.
The fruit flies will smell the fruit and enter the homemade fruit fly trap.
When you have caught a good supply, place the entire jar in the freezer.
After a short time that flies with die and you can remove the jar from the freezer and use it again without even removing the old contents.
Use your homemade trap again and again until your fruit flies are gone.