One of the more interesting details of a recent investigation of the mosquitoes of the Rocky Mountains Park, Alberta, was the finding of Aedes nearcticus Dyar—a mosquito hitherto considered to be restricted to the Arctic regions of Europe and North America. A few specimens were first taken at Lake Louise in 1921, when Mr. Arthur Gibson, the Dominion Entomologist, and the writer made a brief survey of mosquito conditions. In 1922 further specimens came to hand through the kindness of Mr. N. B. Sanson who sent the writer living larvae collected at Simpson's Summit at about 7000 feet. Adults were successfully reared from these. During 1924 and 1925 a number of trips were made by the writer and his assistant, Mr. A. G. Mail, to secure data on this interesting species, and several hundred specimens of larvae, and both sexes of adults were taken.