Anopheles stephensi mosquito larva. The head is at left, the tail at right. The adult Anopheles stephensi female is a known vector for the tropical disease malaria. Malaria is caused by protozoan parasites that are transmitted by the bites of mosquitoes. The blood on which female mosquitoes feed provides them with sustenance for egg production. The eggs are laid in water. After hatching, the larvae develop into the adult form. The protozoan parasites passed into the bloodstream of the host cause periodic fevers and can kill. Malaria affects millions of people in tropical and subtropical regions of the world.