While prevention is the most effective weapon in the fight against fruit flies, you can rely on a basic, do-it-yourself trap made from easily accessible -- and all-natural -- materials when the little pests strike. These homemade traps, which turn the insects' affinity for moisture and sweet organic matter against them, attract and then entrap. You have plenty of options for bait -- an essential part of the equation -- ranging from pungent foods to fermented beverages.
Funnel the flies into a prison from which they can't escape by filling the bottom of a glass jar or similar container -- about a pint in size does the trick -- with fruit fly bait. Use a few ounces of unfiltered apple cider vinegar, sweet fruit juice, leftover wine, rotted fruit or a single banana slice to entice the insects. You can even use a combination of a few splashes of vinegar and water and a drop or so of fruit-scented dish soap. Drop a sturdy piece of paper rolled into the shape of a funnel into the jar with the narrow end down. The wide end should emerge from the jar's mouth, filling it to the rim. As it lets flies in, the cone also keeps them trapped in the container.
Placement and Maintenance
Traps only work if they're near their prey, so place the trap in a fruit fly breeding site. In the home, these sites typically include damp spaces near sinks or dishwashers, underneath bars, in cabinets, near food staging or preparation areas, or any areas in which you store exposed fruit or fermenting food. Empty the trap of flies outdoors -- well away from the house -- daily. While outside, refresh the bait with fresh material and continue to place the traps in the kitchen until the area is free of adult flies.
Alternative Approaches: First Approach
Fill a jar about 2/3 of the way full with apple cider vinegar and a drop of dish detergent, then seal it with plastic wrap and rubber band to make an alternative fly trap. Avoid using more than a drop or two of soap; you need it to break the surface tension of the liquid so the flies will sink into it, but fruit flies recognize soap as a poison. Poke holes in the plastic -- no more than 1/8-inch in diameter -- to allow flies access to the solution. Once inside, the pests will eventually drown in the vinegar. A packet of activated dry yeast, 1/3 cup of warm water and a teaspoon of sugar also works, but this trap needs regular emptying, as the yeast attracts the flies but doesn't drown them.
Alternative Approaches: Second Approach
For another alternative, set a kitchen funnel in a flute-style wine glass filled with a few teaspoons of wine or vinegar. Place and maintain the trap just as you would a jar trap.
More to Consider
To completely eradicate a fruit fly infestation, you need to identify the larval breeding grounds -- typically rotten fruit, ripe trash, a sink drain, or other moist area rich in organic matter -- and dispose of them completely. Likewise, when placing traps, thoroughly clean the area of food debris and spills and refrigerate all produce to keep the flies focused on the bait. As your traps catch adult flies each day, you can transition from emptying and replenishing them daily to once every few days until you eliminate the infestation.