Abstract
Interest in the Canadian north has increased greatly during recent years because of its importance in national defence, and the actual and potential value of its natural resources. A serious hindrance to northern development is the presence during the short summer season of great numbers of blood-sucking flies that make liie difficult for man and beast. The major pem in the forested subarctic are mosquitoes, black flies, and tabanids (the so-called deer flies and moose flies); beyond the tree-line on the arctic tundra black flies are much less troublesome and tabanids do not occur, but in many regions mosquitoes are a terrible scourge.