It is too often assumed that mosquitos in cold climates always adopt one of two methods of passing the winter: Either (1) that with the decline in the atmospheric temperatures in the autumn the adults cease their reproductive functions, and develop a “fat-body” on which they nourish themselves during the winter months while they rest in a semi-dormant condition in situations sheltered from fatally low temperatures; or (2) that with the decline in atmospheric temperatures during the autumn the adults of a particular species die off, and that their larvae, by adopting a semi-dormant state, are able to keep alive in their habitats, even though the water may freeze and enclose them in a block of ice.