I used to make the inverted cone type traps but one day I didn't have any tape so I tried this. Much to my surprise it worked just as well, but was way easier to make.
Fruit flies can be a pain in the kitchen, but with a good trap it's surprising how quickly you can get rid of them.
The steps are:
1. Put bait in the bottom of the container
2. Cover top with plastic wrap
3. Secure with rubber band
4. Poke holes so flies can get in
Step 1: Materials
1. A container
2. Plastic wrap
3. Rubber band
1. Something pointy
Step 2: Choose a Container
You want something small, and hard to knock over (especially if you're baiting it with red wine). I have found the bottom half of a water/pop bottle or a little yogourt container to be ideal.
I like to use disposable plastic containers because the thought of cleaning out a fruit fly hotel does not appeal to me and I'd rather just toss the whole thing at the end.
Step 3: Bait the Trap
Bait the trap by putting a little bit of something yummy in the bottom of the container.
Generally this is whatever the fruit flies are hanging around. Some good standbys are wine, old fruit, bananas/banana peels, and orange juice. It's usually desirable to have some liquid in the bottom so they drown instead of setting up families.
Edit: I've been told cider vinegar is also a good bait. Also, adding a little bit of dish detergent* will encourage drowning.
*Be careful with adding detergent, the green apple detergent I have right now scared all the flies away. A second trap with the same bait and no detergent worked great.
Step 4: Cover With Plastic Wrap and Secure
Cover the container with plastic wrap and secure with a rubber band.
Step 5: Poke Holes
Poke one to four entrance holes in the plastic wrap. Try to imagine how big a fruit fly is and make the hole a little bit bigger than that (say 2 mm). This doesn't have to be precise or clean. Pulling the plastic wrap tight will make this easier.
Step 6: Remove Hiding Spots (op)
Now to really eradicate the little bugs you need to remove their hiding spots. This means removing their access to anything tasty except your trap. Put fruit in the fridge, seal it in plastic bags or cover it tightly. Throw out any fruit thats starting to spoil and take the garbage/compost out. You'll only have to do this for the first couple of days. The more disciplined you are at this the better and faster the trap will work.
In the summer when there's a lot of fruit coming and going I tend to forgo this and just leave a trap out all the time.
Step 7: Freeze 'em (op)
Fruit flies will start breeding really quickly so if you want to keep the trap for more than a few days and not have a fruit fly farm on your counter (trust me you do not) it's a good idea to kill the flies off periodically. The best way I've found of doing this is to put the whole thing in the freezer overnight.