I made a trap by cutting the top off a plastic bottle, inverting it, and put a rotting banana in it. However, not a single fly has gone into the trap for 2 days (and there are flies everywhere).
I'm guessing they simply aren't attracted to bananas. If this is the case, what is the best bait to lure flies?
For more info, I'm in Uruguay, and they appear to be common houseflies.
I would give this sticky tape trick a try http://everydayroots.com/sticky-paper-fly-trap it's an old method. Hope this helps :)
I don't know about houseflies in Uruguay, but here in the Netherlands I always put the following in the bottle trap:
In the past summer I've mostly been bothered by fruit flies, and I caught a buttload of them. But I've also caught a couple of houseflies that were bothering me, this way.
I've successfully used a small pool of orange juice in the bottom of a similar trap to catch fruit flies.
If you can stand the tought and the smell: A small piece of meat.
Some insects are not atracted to sweet but will come in on savory items.
I suggest you cut that banana, immerse into honey and keep it wide open in the setup you have made. Another method is as follows:
Though another answer also used light, I do not support collecting flies in a freezer so I am improving it with another suitable substitute.
Here's a trick for you, provided you are talking about regular flies.
Most answers mentioned a food source. Let's try something else that also attract flies: Light
Flies are attracted to light and will fly toward light sources when their surroundings become dark. Here is what I have had a lot of success with: Be sure you can create total darkness in the house and only produce light where you want to catch the flies. At night, clear out or line the freezer with paper or plastic, then, gradually turn on and off lights around one by one to lure the flies closer to the fridge. Then turn off all light source and open the freezer. If your freezer does not have a light, put a flashlight in there, point it inward. In a couple minutes, you will get all the flies in there. Close the freezer for a minute. All the flies will have dropped frozen and not yet dead. Remember, clear out and/or line your freezer. They flies won't get to land anywhere. They'll freeze and drop into your plastic or paper.
You can then collect them, do what you want with them. Feed the frogs, throw them out to nature, or flush them away.
The same light concept can be used without the freezer. You can use a tube, a large, empty soda bottle, a water jug, so long as you make the light lure really tightly controlled so that it's the only light source. Spread sticky glue around the walls & you will get a jug full of flies.
Have fun!
Your bait could be honey or any syrup that emits a strong smell while seemingly appetizing. Also make sure the smell can escape the container. That could be why the flies are not attracted towards it, as they can not smell it.
