Slugs are drawn to yeasty smelling liquids such as beer. Give it 15 minutes at room temperature to activate the yeast. Keep it in the refrigerator and use it later to rebait the traps. Once attracted to the traps, the slugs fall in and drown. Traps should be checked every day or two, emptied and the bait refreshed.
Slugs are lazy creatures that hide during the day in the nearest cool, dark place.
Lay down a shingle, smoother side down, where you suspect slugs. Pick it up the next day and scrape them off the bottom of the shingle. Another option is a section of wet newspaper, still folded. When you pick it up the next day, you can simply throw it away, slugs and all, and put down a new section the next night. Also, overturned flower pots or saucers work well.