If the vinegar trap feels too peasant-like, raid your own stash. Pour a finger of leftover red wine into a bottle, add a drop of soap, and leave it open. Fruit flies love a good vintage. It’s a little ironic: you drink wine to relax, and they drink wine to die. Circle of life, baby. I once caught 40 flies in a cheap Merlot overnight. It was the most productive that bottle had ever been.