🚫🪰A tip that many people would have known sooner

The detergent breaks down the surface tension of the water. The flies cannot stay afloat and fall into the mixture.
Step 5

Place the container:

    near the fruit basket;
    next to the trash;
    often near an open window;
    or on a terrace with a lot of flies.

In the merits of better results

The trap works even better if:

    replace the mixture every two to three days;
    clean the container regularly;
    Set up several traps in