Have some juice.

Half-glass apple juice with shot of vinegar for more attractive (to fruit fly) smell. Shot of washing-up liquid for (I assume) reduced surface tension.

So they drown. Layer of dead flies forms on surface of juice. Corpses slowly become water(juice)logged. Sink to the bottom slowly, one by one, joining layer there.

The funny thing is, there's still just as many of them around the kitchen, so they must be breeding faster than they're drowning. I suspect natural selection is right now in the process of creating a hyperintelligent species of fruit fly that doesn't like apple juice.

So today I went after them with the hoover. If that doesn't put a sufficient dent in their population for the apple juice traps to finish them off... ...well then god help us all.

(Transmission cuts off. Fade to black, roll credits.)