Mosquito Dunks are a safe, non-toxic way to control mosquitoes before they become flying, biting, disease-carrying adults. It floats on water & will keep on working for 30 days or longer under typical environmental conditions. They slowly release a long-term, biological mosquito larvicide at the water's surface which gradually settles in the water where it is eaten by mosquito larvae. Can be used on all types of containerized standing water sites where mosquito larvae grow, except finished & treated drinking water. Mosquito Dunks will kill the larvae of ALL SPECIES of mosquitos... that's about 2,500 species.