20 count mosquito dunks. Kills Mosquitoes before They're Old Enough to Bite!(TM) With BTI, a bacteria toxic only to mosquito larvae, that lasts 30 days and treats 100 square feet of surface water. Non-toxic to all other wildlife , pets, fish, and humans. Simply apply Mosquito Dunks(TM) to any standing water, or water garden. Kills within hours lasts for 30 days or more. Labeled For Organic Gardening by the USEPA.