Summit Chemical formulated their Mosquito Dunks to kill mosquitoes within hours. Just place the ring on the surface of standing water. As it dissolves, it releases the natural bacterium BTI. The BTI eats any mosquito larvae, regardless of species. The United States EPA approves Mosquito Dunks for organic gardening in all 50 states. While BTI eliminates mosquitoes, it causes no harm to humans, pets, fish, or other wildlife. One ring treats up to 100 square feet of surface area. You can even break the ring apart to treat smaller areas. Each one lasts 30+ days in standing water. Store unused rings indefinitely. Mosquitoes can transmit many diseases. They use any source of standing water to reproduce; this includes water troughs, koi ponds, bird baths, and rain barrels. Use Summit Mosquito Dunks and kill mosquitoes before they are old enough to bite! Also available in a package of 6.