Fruit flies are tiny little flies that are attracted by the fermentation of over ripe, fruits and vegetables, vinegar, fruit juices and yeasts that you might have sitting on your counter in the kitchen or pantry.
If you wish to make a trap to eliminate these little blighters, simply fill a jar with their favorite foods. Like vinegar, over ripe fruit etc. Insert a paper or metal funnel into the mouth of the baited jar. The flies will fly in through the funnel but will not be able to fly out which will help clear out your kitchen of these little pests.