A mason jar, apple cider vinegar, and a drop of dish soap are all you need to build a fly trap that actually works. The whole setup takes about two minutes, costs almost nothing, and can start catching fruit flies within hours. There are a few different designs worth knowing about, since small differences in lid style and hole size make a real difference in how many flies you trap.
The Basic Bait Formula
Pour about 1/4 cup of apple cider vinegar into the jar, then add a few drops of liquid dish soap. That’s the core recipe for every version of this trap. The vinegar mimics the smell of fermenting fruit, which is irresistible to fruit flies. The dish soap breaks the surface tension of the liquid so flies that touch the surface sink and drown instead of standing on it and flying away.
Apple cider vinegar works better than white vinegar because its fermentation scent is stronger. If you don’t have any on hand, the dregs of a red wine bottle with a squirt of dish soap work almost as well. For house flies or larger species, a yeast-based bait (a pinch of active dry yeast mixed with sugar and warm water) produces carbon dioxide that draws them in more effectively than vinegar alone.
Four Lid Designs, Ranked
The bait is only half the equation. What goes on top of the jar determines whether flies get in and stay in.
Holes punched in the metal lid (most effective): Use a hammer and nail to punch several small holes through the flat disc of a standard mason jar lid. Fill the jar with bait, screw the lid on, and set it out. This was the top performer in side-by-side testing by The Kitchn. The small, fixed holes let flies enter but make escape nearly impossible since they’d need to locate a tiny opening from below.
Paper cone funnel: Roll a piece of paper or cardstock into a cone and insert it into the mouth of the jar, narrow end pointing down. Snip the tip so the opening is about 1/8 inch in diameter. Too small and flies can’t enter; too large and they find their way back out. The funnel shape guides flies downward easily, but to escape they’d have to fly straight up and hit that tiny hole, which they almost never manage. Make sure the cone’s wide end sits snugly against the jar rim with no gaps along the edges.
Plastic wrap cover: Stretch plastic wrap tightly over the jar opening and secure it with a rubber band. Poke several small holes with a fork. This works on the same principle as the punched lid, though the wrap can sag over time and the holes tend to be less precise.
Open wine bottle: Leave the last inch of wine in a bottle and add dish soap. The narrow neck acts as a natural funnel. This is the laziest option and catches fewer flies than a jar with a proper lid, but it’s still better than nothing if you have an open bottle sitting around.
Hole Size Matters More Than You Think
The critical measurement is the entry hole diameter. For fruit flies, aim for about 1/8 inch. A standard finish nail creates roughly the right size when punched through a mason jar lid. If you’re using the paper cone method, snip the tip gradually and test the opening before placing it in the jar. You can always cut more off, but you can’t add paper back.
Larger flies like house flies need bigger entry points, closer to 1/4 inch, but fruit flies will escape through holes that size. If you’re dealing with both species, run two separate traps with different hole sizes rather than trying to split the difference.
Where to Place the Trap
Set the jar near the source of the problem. If fruit flies are clustering around your kitchen counter, banana bowl, or compost bin, place the trap within a foot or two of that spot. Flies respond to scent gradients, so the closer the trap is to where they’re already active, the faster they’ll find it.
Keep the trap below counter height or on the counter itself. Research on fly behavior shows traps placed at waist height or lower catch significantly more flies than those positioned higher up. A shelf above the sink is worse than the counter next to it.
Avoid placing traps in direct sunlight. Heat breaks down the vinegar’s scent compounds faster and can warp plastic wrap covers. A shaded spot on the counter or near a window (but not in the sun’s path) is ideal. If you’re setting traps near doorways to intercept flies entering from outside, keep them a few feet inside the door rather than right at the threshold, where drafts disperse the scent.
When to Empty and Replace the Bait
Plan to swap out the bait every one to two weeks. After that, the vinegar loses its potency and the accumulation of dead flies makes the trap less appealing to new ones. If the liquid starts smelling more rotten than tangy, or if the trap is visibly full, it’s time regardless of how many days it’s been.
To dispose of the contents, pour the liquid down the drain and rinse, or dump it into a hole in garden soil and cover it with dirt. The soil acts as a natural odor barrier and the organic material composts quickly. If you’re tossing the whole trap (say, a jar with a ruined lid), seal it in a zip-lock bag first, then place that inside a second bag before putting it in the trash. The double layer prevents leaks and contains the smell, which matters if your garbage doesn’t get picked up for several days.
Wear gloves if you’re handling a trap that’s been sitting for a while. Dead flies in standing liquid breed bacteria quickly. If you spill the contents, clean the area with warm soapy water right away. The longer it sits, the harder the stain and smell are to remove. Keep spills away from pets and kids until the surface is fully dry.
Getting Better Results
A single trap handles a small infestation, but a serious fruit fly problem usually calls for two or three jars spread across the kitchen. Place one near the trash can, one near the fruit bowl, and one near the sink drain if that’s where flies are congregating.
The trap alone won’t solve the problem if the breeding source is still active. Fruit flies lay eggs on overripe produce, in sink drains, and in any moist organic material. Remove or refrigerate ripening fruit, clean drains with a stiff brush, and take out compost regularly. The traps catch the adults; eliminating the breeding site stops the next generation. Used together, you can clear a fruit fly problem in about a week.