Even at this season the Caribou are granted occasional relief from the blood-sucking flies. The characteristic strong winds of that region help greatly in keeping the insects in abeyance. Furthermore, both mosquitoes and black flies become more or less inactive whenever the temperature drops to the neighborhood of 45° (_cf._ Weber, 1950: 196), and this happens fairly frequently even in mid-summer. Finally, the black flies retire during the hours of darkness; and short as these hours are, the relief they bring is very noteworthy. These conditions offer something of a contrast to those surrounding the Woodland Caribou. It is difficult to see how that animal can secure a moment’s respite from mosquito attacks, by day or night, through most of the summer. In its forested habitat there is not sufficient lowering of the temperature nor sufficient penetration of strong winds. Hard as the life of the Barren Ground Caribou may be, it seems to have a few advantages not available to the Woodland Caribou; and possibly it is these that have enabled it to attain a vastly greater population than the other species. Of 52 mosquito specimens brought back from the Windy River area, 39 were _Aedes nearcticus_ Dyar, 2 were probably _Aedes fitchii_ (F. and Y.), and the remaining 11 were of the same genus but not in condition for specific determination (_cf._ Dyar, 1919; Weber, 1950: 196). _Ae. nearcticus_ is holarctic in distribution; in North America it occurs chiefly on the Barren Grounds, but is known from as far south as Montana. _Ae. fitchii_ ranges through the northern United States and Canada, north to the limit of trees. Of 26 black flies, all were _Simulium venustum_ Say, which occurs in northern Europe, Alaska, and Labrador, south to the Adirondacks, Illinois, Iowa, Georgia, and Alabama. (Names and ranges supplied by Dr. Alan Stone, of the United States Bureau of Entomology and Plant Quarantine.) These mosquitoes and black flies were presumably the species attacking the Caribou in the Nueltin Lake region.