Sure, there are A LOT of things that kill fruit flies, like vacuums, newspapers rolled up, blow torches, and baseball bats, but some of those are probably not the most practical options for your kitchen.  When it comes to figuring out what kills fruit flies, the solution is simple:  

what kills fruit fliesCredit: http://www.flickr.com/photos/spazticus/2709258188/

Get a small cereal bowl and fill it up halfway with a sweet liquid.  Things like cider vinegar and fruit juice work great.  Add a drop of kitchen dish soap and set the bowl out where the fruit flies are heaviest.  Sit back and watch them fly into the irresistible trap.  They'll get stuck and drown in the bowl--that's what kills fruit flies.  Eventually, you will see it fill up with dead gnats at the bottom.  At that point, it's a good idea to empty the contents so you don't get grossed out every time you walk into the kitchen.  

It is as simple as that, but if you want to know about some other fruit fly traps (the homemade kind), here are two other simple ideas: 

  • Ziplock trap - get a ziplock bag and leave a small opening.  Put some rotting fruit in there and wait for the bag to fill up with fruit flies.  They will be smart enough to get in, but will likely get lost finding their way out.  Most fruit flies are pretty dumb when it comes to directions.  Once you have a bag crawling with gnats, seal it up and throw it away.  
  • Jar with a small opening - Get a jar, put a piece of rotting fruit in there (and/or other attractants like wine, beer, fruit juice, etc.), and seal it with a piece of Saran Wrap.  I use a rubber band to keep the wrap in place.  Now make a few small holes in the Saran Wrap with a fork or a toothpick and wait for the pesky bugs to get trapped inside.  Once again, they will have trouble figuring their way out of there.   

Fruit flies in the house are no fun at all.  The long-term solution to fruit flies is proper sanitation and understanding where fruit flies come from, but the tips in this article will get you on the right path quickly.   Now you know what kills fruit flies, so good luck getting rid of those unwanted house guests!