Mosquito Dunks can be placed in standing water to kill larvae before they are old enough to bite. This product is safe to use in fish habitats, flower pots, roof gutters, bird baths, and even animal watering troughs. Mosquito Dunks float in water, work for 30 days or more, and release larvicide that, once settled, will be ingested by larvae. Sold in packs of 6 rings for areas up to 100 square feet. Each ring can be used whole or broken into portions for use in any area of any size.