* Make a cone out of the sheet of paper (like a funnel). Tape the outside of the cone so that it stays in place.
* Check that the cone fits snugly into a glass or cup.
* Cut off the tip of the cone so that you now have a funnel.
* Pour a small amount of cider vinegar into the glass or cup. (Rum mixed with orange juice also works very well - additionally, a half teaspoon of baker's yeast in water can also suffice)
* Insert the funnel into the glass or cup, but don't let the bottom of the funnel touch the liquid. Tape the funnel in two or three places from the outside so that there is no gap between the glass and the cone.
* Place your newly created trap on a flat surface. The flies will be attracted by the smell of the fruity vinegar and fly into the cone. The flies will slip down the cone and will either land in the vinegar and drown or will be trapped and not able to get back out. If you leave the trap overnight, the trapped fruit flies will eventually fall into the vinegar and drown.
Make sure your choose right type of vinegar. White vinegar does not work. Malt vinegar and red wine work, just not as well. Beer sometimes works, too. Balsamic vinegar also works well. Wine works extremely well, and a wine bottle with an inch or so left can be used without an additional funnel.
You can forgo the funnel if you put a small bit of dishwashing detergent in the cup with the vinegar and stir. The fruit flies are still attracted to the vinegar smell, and the detergent traps them. The detergent actually reduces the surface tension of the liquid allowing the flies to more readily sink and drown.
