I have used five of these in my garden for a number of years. To be truly successful, set them out in the spring before slugs start eating, fill slots with beer, place cover to prevent beer being diluted with water and leave them alone until end of summer when you clean them out. If infestation really bad, mid summer clean them out and put in fresh beer. These traps especially effective placed under hostas, which slugs love. Every year I'm seeing a reduction in number of slugs I had at one time.