This fruit fly trap features a uniquely designed dome and specially formulated food grade liquid. The attractant lures fruit flies in through a small hole, this hole has a reverse cone feature to prevent them from exiting the trap. The flies eventually drown in the liquid. This trap sits flat, but when combined with the holder it works vertical and even upside down. Each trap will last up to 30 days, but will usually fill up before then. All you do is peel the top sticker and the trap is good to go!