Just FYI, this type of trap, (scroll down to ‘eradication’) baited with a banana peel, is eerily effective. Summer in the South combined with the delicious wares of less-than-reputable produce stands makes them a constant nuisance, even in a clean kitchen (which, let me just say, mine is not). My carnivorous plants can’t eat ‘em all, though Sundews (Drosera spp) and butterworts (Pinguicula spp) put up a good fight. Enough to where their leaves can essentially choke to death on the overabundance of little winged nutrient balls.
So last night I put a half an overripe banana in a jar, then stuck a paper funnel down inside. Within 20 minutes, I had caught 10 or so. By morning I had a writhing Molotov cocktail of Drosophila, ready to bwe thrown through the windows of my enemies.
I always have a hard time describing the trap. This illustration pretty much covers it–the paper funnel has a small opening that sits down in the jar, and you tape the juncture where the funnel meets the mouth of the jar. Fruit flies climb down the funnel to get to the bait, but when they try to leave, they inevitably fly up, getting stuck at the side of funnel/mouth of jar junction. Once you’ve hoovered them all up, either dump the contents into your compost or start a genetics lab.