I don't know how this works but it works and it does a wonderful job we have no more flies in the backyard coming into the house. Our neighbor has a big dog in a kennel and they do not clean up the poop they just throw it to the corner of the fence. So we have a very large population of flies. I put this out it says it has to cure for three days, the next morning I went out there and I couldn't even count how many flies when. The flies go in they can't figure out how to get back out the whole there's four of them they fly around to their exhausted and then fall into the liquid and drown. What I like about it is that it is non-toxic. The next time I buy one I'm going to buy the smaller size as I have nerve damage and it is hard for me to use the large size. My recommendation is to clean this out and change the bait after one week if you have a lot of flies in their. I didn't do this and I guess the decomposing flies may liquid that filled the whole container up which I had to throw away. This is a great product and it really works. Please pardon any grammatical errors I have to dictate to my computer as I'm a disabled veteran.