A Mosquito Dunk® looks like a small, beige donut which floats on standing water. As the Dunk® slowly dissolves, it releases a bacterium which is toxic to all species of mosquito larvae. The active ingredient in Mosquito Dunks® is Bacillus thuringiensis subspecies israelensis (Bti). Bti is a bacterium that is deadly to mosquito larvae but harmless to other living things. Just float a biodegradable Mosquito Dunk® in water troughs, koi ponds, birdbaths, rain barrels, animal watering troughs, elevator shafts, or any place where water collects and remains for periods of time. While floating, a Mosquito Dunk® slowly releases a long-term biological mosquito larvicide at the water's surface. This larvicide gradually settles in the water, and while it travels through the water it is eaten by the mosquito larvae growing there. When female mosquitoes lay their eggs in standing water treated with a Mosquito Dunk®, the larvae will hatch and begin to eat the Bti. The Bti will kill the mosquito larvae before they can grow up to become biting and disease-spreading adults. Each Mosquito Dunk® will effectively treat 100 square feet of surface water for 30 days or more. For less water, a portion of a Mosquito Dunk® can be used. Homeowners, ranchers and farmers looking for a safe, nontoxic way to control mosquitoes can use Mosquito Dunks®, which kill mosquitoes before they can become flying, biting, disease-carrying adults.