Cover a jar of bait with cling film, poke a few tiny holes, and you have built a one-way door that fruit flies can walk through but almost never walk back out of. It is the upgrade that turns an ordinary open dish into a proper trap, using nothing you don't already have in a kitchen drawer. Here is exactly how to build it, why the pinholes are the whole secret, and how to make it work harder.
In short
- What you need
- A jar or glass, cling film, an elastic band, a toothpick, and a liquid bait
- How it traps
- Flies enter through pinholes drawn by the smell, then can't relocate the holes to leave
- Time to make
- Three to four minutes
- Best bait
- Apple cider vinegar, or vinegar with a chunk of ripe fruit
- Bonus
- Covered design keeps the smell contained and pets out
Why cover the jar at all?
An open dish of vinegar catches flies mainly because they land, touch the soapy liquid and sink. It works, but plenty of flies visit, hover, and leave again without ever landing. The plastic-wrap version closes that escape route. By sealing the top and leaving only a scatter of pinholes, you create a container that flies find easy to enter and very hard to exit — a classic insect trap geometry. Once inside the dim, enclosed space, they orient toward the light coming through the sides and the smell rising off the bait, and they simply cannot find the small holes in the taut film again. It is the same one-way principle as the bottle funnel trap, just built from cling film instead of a cut bottle.
Step-by-step recipe
- Choose a jar or glass. A jam jar, drinking glass or mug all work. A wider mouth gives flies more surface to be drawn toward; a taller jar keeps pets and children away from the liquid.
- Add the bait. Pour in 2–3 cm of apple cider vinegar. A drop of dish soap is optional here — the cover does most of the trapping — but adding it makes the trap doubly effective by drowning any fly that lands. For a stronger lure, drop in a slice of overripe banana or a squashed grape.
- Stretch cling film over the top. Pull a square of plastic wrap tight and flat across the opening, then wrap an elastic band around the rim to hold it drum-tight. A loose, saggy film lets flies slip under the edge instead of through the holes.
- Poke the pinholes. Using a toothpick, cocktail stick or a sharp pencil, make five to eight small holes in the film. Keep them genuinely small — about the width of a matchstick. Big holes let flies leave as easily as they arrive.
- Place and wait. Set the jar where the flies are busiest and leave it. Check after a few hours; you will usually see the first arrivals drifting down through the holes.
Tip: Warm the bait slightly by leaving the jar in a warm spot for a few minutes before covering it. A warmer liquid releases more scent, and a stronger smell plume pulls flies from further across the room.
The pinholes: getting them right
The single detail that decides whether this trap thrives or flops is the size and number of the holes. Get them too big and the trap becomes a doorway in both directions; too few and hardly any flies find their way in.
Do
- Keep holes small — matchstick width or less
- Make five to eight of them, spread across the film
- Pull the film tight so it stays flat and taut
- Angle a couple of holes near the centre, over the bait
Avoid
- One or two large holes — flies escape easily
- A loose, wrinkled film with gaps at the edge
- Dozens of holes that weaken the film and tear it
- Holes so tiny the smell can't escape to attract anything
How the flies actually behave
It helps to picture what a fruit fly does at the trap. Drawn by the fermentation scent leaking through the film, it lands on top, walks around, and eventually drops through one of the pinholes toward the smell — flies naturally move downward and inward toward a food source. Once below the film, it feeds or lands on the liquid. When it tries to leave, it flies upward and outward toward the brightest light, which is the glass sides, not the small dark holes above the bait. It bumps the film, rests, tries again, and stays put. This gap between how they enter and how they try to exit is exactly why the trap works. If yours is letting flies escape, our guide to why your trap isn't working covers the usual culprits.
Bait choices for the jar
The cover works with almost any fermented lure, so match the bait to what you have. Apple cider vinegar is the dependable default and gets its own full recipe in the apple cider vinegar trap. A splash of red wine or flat beer works just as well and is covered in the wine, beer and yeast trap. For the strongest possible pull, combine vinegar with a piece of genuinely rotting fruit as described in the rotten fruit trap. Whichever you choose, our overview of the best bait for fruit flies ranks them so you can pick with confidence.
Note: Because the jar is sealed, this trap is a good choice near a bin or in a pantry where an open dish would be knocked over or investigated by a curious pet. The film keeps the smell — and the drowned flies — neatly contained.
Placement and how long to run it
Set the jar at the heart of the activity: beside the fruit bowl, next to the bin, or by the sink where flies congregate. Run it for two to three days, then refresh the bait once the smell fades or the surface fills with flies. For a heavier infestation, build two or three jars and spread them across the hotspots rather than relying on one. Our room-by-room guide to where to place fruit fly traps helps you pick the winning spots.
Remember: trapping is only half the fix
A jar trap, however well built, only removes the adults currently flying. New ones keep hatching from eggs hidden in a drain film, a spill, a forgotten vegetable or the fruit itself — so the trap must run alongside a proper clean-up, not instead of one. Track down what they are breeding in using how to find the breeding source, then follow the structured five-day fruit fly plan. For the wider strategy and every trap style side by side, start at the traps hub or the main remove fruit flies guide.
Sources
- University of Minnesota Extension — homemade fruit fly traps and household control
- University of Kentucky Entomology — fruit fly biology and trapping
- Illinois Extension — DIY jar-and-wrap fruit fly traps
- Penn State Extension — vinegar flies in the home